原文地址:http://blog.csdn.net/u012702547/article/details/52273918
Picasso是Squareup公司出的一款圖片加載框架,能夠解決我們在Android開發中加載圖片時遇到的諸多問題,比如OOM,圖片錯位等,問題主要集中在加載圖片列表時,因爲單張圖片加載誰都會寫。如果我們想在ListView或者GridView或者RecyclerView中加載圖片牆,那麼這個時候對原圖片的二次處理就顯得非常重要了,否則就會出現我們上文說的OOM或者圖片錯位等。不過,如果你使用了Picasso來加載圖片的話,那麼所有問題都會變得很簡單。OK,那我們今天就來看看Picasso的使用。
1.基本使用
Picasso加載一張網絡圖片,最簡單的一行代碼就搞定:
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Picasso.with(this).load("http://n.sinaimg.cn/translate/20160819/9BpA-fxvcsrn8627957.jpg").into(iv);
如果你想對這張圖片進行剪裁,可以使用resize方法:
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Picasso.with(this).load("http://n.sinaimg.cn/translate/20160819/9BpA-fxvcsrn8627957.jpg")
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.resize(200,200)
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.into(iv);
注意這裏的200表示200px,如果你想在resize時指定dp,可以使用如下方法:
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Picasso.with(this).load("http://n.sinaimg.cn/translate/20160819/9BpA-fxvcsrn8627957.jpg")
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.resizeDimen(R.dimen.iv_width,R.dimen.iv_height)
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.into(iv);
在dimen文件中定義寬高即可:
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<dimen name="iv_width">200dp</dimen>
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<dimen name="iv_height">200dp</dimen>
其實我們看看resizeDimen的源碼就知道它是怎麼設置dp了:
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public RequestCreator resizeDimen(int targetWidthResId, int targetHeightResId) {
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Resources resources = picasso.context.getResources();
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int targetWidth = resources.getDimensionPixelSize(targetWidthResId);
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int targetHeight = resources.getDimensionPixelSize(targetHeightResId);
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return resize(targetWidth, targetHeight);
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}
一句話,它就是把dp讀取成px然後調用resize方法實現的。
OK,很多時候我還可以給Picasso下載的圖片設置縮放模式,也就是ImageView的ScaleType屬性(不瞭解的請移步這裏),但是注意,縮放模式centerCrop和centerInside要和resize一起使用,否則會拋異常,而縮放模式fit不可以和resize一起使用,如下:
使用fit:
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Picasso.with(this).load("http://n.sinaimg.cn/translate/20160819/9BpA-fxvcsrn8627957.jpg")
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.fit()
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.into(iv);
使用centerCrop:
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Picasso.with(this).load("http://n.sinaimg.cn/translate/20160819/9BpA-fxvcsrn8627957.jpg")
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.resizeDimen(R.dimen.iv_width,R.dimen.iv_height)
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.centerCrop()
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.into(iv);
很多時候我們在圖片加載出來之前需要先顯示一張默認圖片,也即佔位圖,而在圖片加載出錯的時候我們可能想顯示一張錯誤圖,這個Picasso也是支持的:
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Picasso.with(this).load("http://n.sinaimg.cn/translate/20160819/9BpA-fxvcsrn8627957.jpg")
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.placeholder(R.mipmap.ic_launcher)
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.error(R.mipmap.ic_launcher)
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.into(iv);
很多時候,我們可能想顯示一個用戶圖像,但是這個用戶圖像是個圓形圖片,這個用Picasso該怎麼實現呢?首先定義一個Transformation,在transform方法中對圖片進行二次處理,包括剪裁重新處理等等,那我這裏想把原圖變爲一個圓形圖,就可以按下面的寫法來:
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Transformation transformation = new Transformation() {
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@Override
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public Bitmap transform(Bitmap source) {
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int width = source.getWidth();
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int height = source.getHeight();
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int size = Math.min(width, height);
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Bitmap blankBitmap = Bitmap.createBitmap(width, height, Bitmap.Config.ARGB_8888);
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Canvas canvas = new Canvas(blankBitmap);
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Paint paint = new Paint();
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paint.setAntiAlias(true);
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canvas.drawCircle(size / 2, size / 2, size / 2, paint);
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paint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.SRC_IN));
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canvas.drawBitmap(source, 0, 0, paint);
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if (source != null && !source.isRecycled()) {
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source.recycle();
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}
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return blankBitmap;
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}
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@Override
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public String key() {
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return "squareup";
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}
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};
paint的setXfermode表示最終顯示的圖形取所繪製圖形的交集,我這裏先繪製了圓形,又繪製了一個矩形的Bitmap,圓形沒有Bitmap大,所以交集肯定是圓形,所以最終顯示結果就爲圓形,在加載圖片的時候可以通過transform屬性來使用自定義的這個transformation,如下:
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Picasso.with(this).load("http://n.sinaimg.cn/translate/20160819/9BpA-fxvcsrn8627957.jpg")
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.transform(transformation)
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.into(iv);
最終顯示結果如下:
依照這個思路,你想把圖像做成什麼形狀都可以了吧!
Picasso還可以通過開啓指示器,讓你看到這個圖片是從內存加載來的還是從SD卡加載來的還是從網絡加載來的,設置方式如下:
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Picasso picasso = Picasso.with(this);
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picasso.setIndicatorsEnabled(true);
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picasso.load("http://n.sinaimg.cn/translate/20160819/9BpA-fxvcsrn8627957.jpg")
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.into(iv);
開啓之後,圖片的加載效果如下:
左上角會有一個藍色的三角符號,不同的顏色表示圖片的來源不同,紅、藍、綠三種顏色分別代表網絡、SD卡和內存。
現在大部分的圖片緩存框架都是支持三級緩存的,在Picasso中,我們也可以手動設置緩存策略,比如說當我們查看一張大圖的時候,可能由於圖片太大,不想將其緩存在內存中,那麼可以自定義緩存策略,如下:
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Picasso picasso = Picasso.with(this);
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picasso.setIndicatorsEnabled(true);
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picasso
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.load("http://n.sinaimg.cn/translate/20160819/9BpA-fxvcsrn8627957.jpg")
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-
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.memoryPolicy(MemoryPolicy.NO_CACHE, MemoryPolicy.NO_STORE)
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.into(iv);
當然,如果你想給圖片加載過程設置一個監聽器也是可以的,如下:
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Picasso picasso = Picasso.with(this);
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picasso.setIndicatorsEnabled(true);
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picasso
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.load("http://n.sinaimg.cn/translate/20160819/9BpA-fxvcsrn8627957.jpg")
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-
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.memoryPolicy(MemoryPolicy.NO_CACHE, MemoryPolicy.NO_STORE)
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.into(iv, new Callback() {
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@Override
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public void onSuccess() {
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Log.d("google_lenve_fb", "onSuccess: 圖片加載成功!");
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}
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@Override
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public void onError() {
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Log.d("google_lenve_fb", "onSuccess: 圖片加載失敗!");
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}
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});
在ListView或者RecyclerView中加載圖片時,當列表處於滑動狀態的時候,我們可以停止圖片的加載,當列表停止滾動的時候,我們又可以繼續加載圖片,如下:
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Object tag = new Object();
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Picasso with = Picasso.with(this);
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with.load("http://n.sinaimg.cn/translate/20160819/9BpA-fxvcsrn8627957.jpg")
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.into(iv);
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with.pauseTag(tag);
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with.resumeTag(tag);
這裏要傳遞的對象可以是任意對象,這兩個方法的使用需要我們自己去監聽ListView或者GridView的滑動狀態。OK,以上這些都屬於Picasso的一個基本使用,接下來我們來看看一些高級使用技巧。
2.自定義緩存位置
既然我們知道Picasso自帶三級緩存,那麼問題就來了,存儲在SD卡的圖片到底存儲在哪裏呢?在手機的內部存儲中,即 /data/data/應用包名/cache 目錄下,這個目錄如果你有root權限就可以查看,可是有的時候我們需要自定義緩存位置,即不想將圖片緩存在這裏,又該怎麼辦?說到這裏,我們不得不來看看Picasso的源碼,with方法源碼如下:
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public static Picasso with(Context context) {
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if (singleton == null) {
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synchronized (Picasso.class) {
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if (singleton == null) {
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singleton = new Builder(context).build();
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}
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}
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}
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return singleton;
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}
大家看到,with方法返回了一個Picasso的單例,在創建Picasso的過程中,調用了new Builder(context).build()方法,說明Picasso實例創建的代碼在build方法中,那我們再來看看這個build方法:
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public Picasso build() {
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Context context = this.context;
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if (downloader == null) {
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downloader = Utils.createDefaultDownloader(context);
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}
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if (cache == null) {
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cache = new LruCache(context);
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}
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if (service == null) {
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service = new PicassoExecutorService();
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}
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if (transformer == null) {
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transformer = RequestTransformer.IDENTITY;
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}
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Stats stats = new Stats(cache);
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Dispatcher dispatcher = new Dispatcher(context, service, HANDLER, downloader, cache, stats);
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return new Picasso(context, dispatcher, cache, listener, transformer, requestHandlers, stats,
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defaultBitmapConfig, indicatorsEnabled, loggingEnabled);
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}
我們先不急着看build中的其他方法,先來看看downloader這個判斷(如果我使用with方法downloader肯定爲null),如果downloader爲null,則系統會幫我們創建一個默認的downloader,那我們來看看這個默認的downloader是怎麼創建的:
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static Downloader createDefaultDownloader(Context context) {
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try {
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Class.forName("com.squareup.okhttp.OkHttpClient");
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return OkHttpLoaderCreator.create(context);
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} catch (ClassNotFoundException ignored) {
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}
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return new UrlConnectionDownloader(context);
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}
啊哈,這裏就很明白了,系統通過反射來檢查我們在項目中是否使用了OkHttp,如果使用了,就使用OkHttp來創建一個下載器,否則就使用HttpUrlConnection來創建一個下載器,可是大家注意Class.forName("com.squareup.okhttp.OkHttpClient");這個方法的參數,這是OkHttp3以前的寫法,現在我們都是使用OkHttp3了,OkHttp3的包名就不是這個樣子,而是okhttp3.OkHttpClient,所以即使你在項目中引用了OkHttp3,Picasso還是會把HttpUrlConnection當作下載器來下載圖片的,這個問題估計Picasso會在以後的版本中修正吧!OK,那如果我們想要使用自己的下載器又該怎麼做呢?其實很簡單,首先不使用with這個方法來初始化Picasso,而是使用Builder來初始化,在初始化的過程中傳入自己的下載器,自己的下載器我們可以模仿Picasso裏邊的這個下載器來寫,也可以自定義,我們來看一個Demo:
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Picasso picasso = new Picasso.Builder(this)
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.downloader(new OkHttp3Downloader(this.getExternalCacheDir()))
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.build();
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Picasso.setSingletonInstance(picasso);
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picasso.load("http://n.sinaimg.cn/translate/20160819/9BpA-fxvcsrn8627957.jpg").into(iv);
使用Builder來構建一個Picasso,在構建的過程中傳入自己的下載器,這個下載器我沒有自己來寫,使用GitHub上的開源項目https://github.com/JakeWharton/picasso2-okhttp3-downloader,裏邊的代碼也都很簡單,只有一個類,拷貝到你的項目中就可使用,不贅述。這樣修改之後,Picasso的圖片緩存位置就發生了改變,存到了
/storage/sdcard/Android/data/應用包名/cache 文件夾中,不同手機這個地址前面一部分可能會有一點點差異。使用這個方法初始化的時候,還調用了setSingletonInstance方法,我們來看看這個方法:
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public static void setSingletonInstance(Picasso picasso) {
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synchronized (Picasso.class) {
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if (singleton != null) {
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throw new IllegalStateException("Singleton instance already exists.");
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}
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singleton = picasso;
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}
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}
這個主要是用來檢查Picasso的單例模式,如果Picasso不是單例的,則LruCache會失效,原因很簡單,如果Picasso不是單例的,每一個Picasso都有自己的LruCache,那麼LruCache本身的功能當然會失效。這一點需要注意。
3.自定義下載線程池
關於Android開發中線程池,如果你還不瞭解,可以參考Android開發之線程池使用總結,使用Picasso下載圖片的時候,系統內部也是有一個線程池,想看這個,我們還是得回到build方法:
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public Picasso build() {
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Context context = this.context;
-
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if (downloader == null) {
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downloader = Utils.createDefaultDownloader(context);
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}
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if (cache == null) {
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cache = new LruCache(context);
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}
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if (service == null) {
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service = new PicassoExecutorService();
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}
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if (transformer == null) {
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transformer = RequestTransformer.IDENTITY;
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}
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Stats stats = new Stats(cache);
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Dispatcher dispatcher = new Dispatcher(context, service, HANDLER, downloader, cache, stats);
-
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return new Picasso(context, dispatcher, cache, listener, transformer, requestHandlers, stats,
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defaultBitmapConfig, indicatorsEnabled, loggingEnabled);
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}
在build方法中還有一個判斷,如果service爲null,則新創建一個PicassoExecutorService,我們來看看這個PicassoExecutorService:
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class PicassoExecutorService extends ThreadPoolExecutor {
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private static final int DEFAULT_THREAD_COUNT = 3;
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-
PicassoExecutorService() {
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super(DEFAULT_THREAD_COUNT, DEFAULT_THREAD_COUNT, 0, TimeUnit.MILLISECONDS,
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new PriorityBlockingQueue<Runnable>(), new Utils.PicassoThreadFactory());
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}
-
-
....
-
....
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}
大家看到,這個PicassoExecutorService繼承自ThreadPoolExecutor這個線程池,線程池中的核心線程數爲3,線程池的最大線程數也爲3,說明線程池中沒有非核心線程,線程隊列使用了PriorityBlockingQueue,說明所有加載進來的任務都將實現Comparator接口。OK,這是系統默認幫我們創建的線程池,如果你想修改,可以在創建Picasso實例的時候傳入自己的線程池:
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int CPU_COUNT = Runtime.getRuntime().availableProcessors();
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ThreadPoolExecutor threadPoolExecutor = new ThreadPoolExecutor(CPU_COUNT + 1, CPU_COUNT * 2 + 1,
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1, TimeUnit.MINUTES, new PriorityBlockingQueue<Runnable>());
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Picasso picasso = new Picasso.Builder(this)
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.executor(threadPoolExecutor)
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.downloader(new OkHttp3Downloader(this.getExternalCacheDir()))
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.build();
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Picasso.setSingletonInstance(picasso);
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picasso.load("http://n.sinaimg.cn/translate/20160819/9BpA-fxvcsrn8627957.jpg").into(iv);
對線程池的創建如果還不瞭解的話,請參考Android開發之線程池使用總結。
4.自定義下載進度條
我在之前的一篇文章中專門介紹過自定義進度條,沒看過的小夥伴請戳這裏Android自定義View之ProgressBar出場記。那我們今天就給Picasso加載圖片的過程也來一個進度條,先來看看顯示效果吧:
整體思路其實很簡單,最關鍵是你要會用OkHttp。
經過上文的講解,小夥伴們已經知道,我可以在構造一個Picasso實例的時候給它設置一個下載器,這個下載器是由OkHttp實現的,在這個下載器中我可以修改Picasso所加載圖片的存儲位置,同理,下載器中我也可以傳遞一個OkHttpClient作爲構造參數(上文使用了緩存文件夾作爲構造參數),我們來看看:
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public OkHttp3Downloader(OkHttpClient client) {
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this.client = client;
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this.cache = client.cache();
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}
大家看到,如果我使用OkHttpClient作爲構造參數,那麼緩存位置則爲OkHttpClient的緩存地址。而在OkHttpClient中有一個攔截器,我們可以在攔截器中來計算當前下載百分比,整體思路就是這樣,我們來看看實現過程:
首先我來定義一個接口,這個接口用來更新我的進度條:
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public interface ProgressListener {
-
-
public void update(@IntRange(from = 0, to = 100) int progress);
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}
然後定義一個OkHttpClient對象,在定義的過程中給OkHttpClient添加攔截器:
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OkHttpClient client = new OkHttpClient.Builder()
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.addNetworkInterceptor(new Interceptor() {
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@Override
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public Response intercept(Chain chain) throws IOException {
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Response response = chain.proceed(chain.request());
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return response.newBuilder()
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.body(new MyProgressbarResponseBody(new ProgressListener() {
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@Override
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public void update(@IntRange(from = 0, to = 100) final int progress) {
-
-
runOnUiThread(new Runnable() {
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@Override
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public void run() {
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Log.d("google_lenve_fb", "run: " + progress);
-
myPb.setSweepAngle(progress * 360f / 100);
-
}
-
});
-
}
-
}, response.body()))
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.build();
-
}
-
})
-
-
.cache(new Cache(this.getExternalCacheDir(), 10 * 1024 * 1024))
-
.build();
大家看到,這裏核心的代碼要算addNetworkInterceptor中的代碼了,OkHttp中的攔截器有點類似於JavaWeb中的過濾器 ,在所有的請求到達Servlet之前,先對其進行一個簡單的處理。而OkHttp中的攔截器,我們可以觀察,修改請求和響應,大多數情況下我們使用攔截器來添加、移除、轉換請求或者響應的頭信息。OK,那麼在本案例中我重新修改了Response的body屬性,給它傳入兩個參數,一個就是剛剛定義的監聽器,還有一個就是response的body,我們來看看這個MyProgressbarResponseBody,如下:
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public class MyProgressbarResponseBody extends ResponseBody {
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private ResponseBody responseBody;
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private ProgressListener progressListener;
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private BufferedSource bufferedSource;
-
-
public MyProgressbarResponseBody(ProgressListener progressListener, ResponseBody responseBody) {
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this.progressListener = progressListener;
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this.responseBody = responseBody;
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}
-
-
@Override
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public MediaType contentType() {
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return responseBody.contentType();
-
}
-
-
@Override
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public long contentLength() {
-
return responseBody.contentLength();
-
}
-
-
@Override
-
public BufferedSource source() {
-
if (bufferedSource == null) {
-
bufferedSource = Okio.buffer(source(responseBody.source()));
-
}
-
return bufferedSource;
-
}
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private Source source(Source source) {
-
-
return new ForwardingSource(source) {
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long totalBytesRead = 0L;
-
-
@Override
-
public long read(Buffer sink, long byteCount) throws IOException {
-
long bytesRead = super.read(sink, byteCount);
-
totalBytesRead += bytesRead != -1 ? bytesRead : 0;
-
if (progressListener != null) {
-
progressListener.update(
-
((int) ((100 * totalBytesRead) / responseBody.contentLength())));
-
}
-
return bytesRead;
-
}
-
};
-
}
-
}
MyProgressbarResponseBody繼承自ResponseBody,並重寫它裏邊的三個方法,分別返回數據類型,數據大小等信息,在source方法中我們來統計當前下載百分比,並且回調監聽器中的接口。最後再來看一眼自定義的ProgressBar,對這個如果還不瞭解,請參考Android自定義View之ProgressBar出場記 。
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public class MyProgressBar extends View {
-
-
-
-
private static final int DEFAULTWIDTH = 200;
-
-
-
-
private static final int DEFAULTHEIGHT = 200;
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private Paint sweepPaint;
-
private int padding = 20;
-
-
-
-
private int sweepColor = getResources().getColor(R.color.pbColor);
-
-
-
-
private int startAngle = -90;
-
-
-
-
private float sweepAngle = 0;
-
-
public MyProgressBar(Context context) {
-
this(context, null);
-
}
-
-
public MyProgressBar(Context context, AttributeSet attrs) {
-
this(context, attrs, 0);
-
}
-
-
public MyProgressBar(Context context, AttributeSet attrs, int defStyleAttr) {
-
super(context, attrs, defStyleAttr);
-
setAlpha(0.8f);
-
sweepPaint = new Paint();
-
sweepPaint.setColor(sweepColor);
-
sweepPaint.setAntiAlias(true);
-
}
-
-
@Override
-
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
-
super.onMeasure(widthMeasureSpec, heightMeasureSpec);
-
-
int widthMode = MeasureSpec.getMode(widthMeasureSpec);
-
-
int widthSize = MeasureSpec.getSize(widthMeasureSpec);
-
-
int heightMode = MeasureSpec.getMode(heightMeasureSpec);
-
-
int heightSize = MeasureSpec.getSize(heightMeasureSpec);
-
switch (widthMode) {
-
case MeasureSpec.EXACTLY:
-
break;
-
case MeasureSpec.AT_MOST:
-
case MeasureSpec.UNSPECIFIED:
-
-
widthSize = (int) TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP, DEFAULTWIDTH, getResources().getDisplayMetrics());
-
break;
-
}
-
switch (heightMode) {
-
case MeasureSpec.EXACTLY:
-
break;
-
case MeasureSpec.AT_MOST:
-
case MeasureSpec.UNSPECIFIED:
-
heightSize = (int) TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP, DEFAULTHEIGHT, getResources().getDisplayMetrics());
-
break;
-
}
-
widthSize = heightSize = Math.min(widthSize, heightSize);
-
-
setMeasuredDimension(widthSize, heightSize);
-
}
-
-
@Override
-
protected void onDraw(Canvas canvas) {
-
if (sweepAngle != 360 && sweepAngle != 0) {
-
RectF oval = new RectF(padding, padding, getWidth() - padding, getHeight() - padding);
-
Log.d("google_lenve_fb", "onDraw: " + sweepAngle);
-
canvas.drawArc(oval, startAngle, sweepAngle, true, sweepPaint);
-
}
-
}
-
-
public void setSweepAngle(float sweepAngle) {
-
this.sweepAngle = sweepAngle;
-
if (Build.VERSION.SDK_INT > 15) {
-
postInvalidateOnAnimation();
-
} else {
-
ViewCompat.postInvalidateOnAnimation(this);
-
}
-
}
-
}
最後,加載一張網絡圖片幾個,注意下載器的創建方式:
-
Picasso picasso = new Picasso
-
.Builder(this)
-
.downloader(new OkHttp3Downloader(client))
-
.build();
5.Picasso源碼剖析
其實我們在上文已經涉及到一些源碼方面的東西了,那麼接下來我們就來理一理Picasso加載圖片的整體思路,首先還是先從with方法開始,進入到build方法中:
-
public Picasso build() {
-
Context context = this.context;
-
-
if (downloader == null) {
-
downloader = Utils.createDefaultDownloader(context);
-
}
-
if (cache == null) {
-
cache = new LruCache(context);
-
}
-
if (service == null) {
-
service = new PicassoExecutorService();
-
}
-
if (transformer == null) {
-
transformer = RequestTransformer.IDENTITY;
-
}
-
-
Stats stats = new Stats(cache);
-
-
Dispatcher dispatcher = new Dispatcher(context, service, HANDLER, downloader, cache, stats);
-
-
return new Picasso(context, dispatcher, cache, listener, transformer, requestHandlers, stats,
-
defaultBitmapConfig, indicatorsEnabled, loggingEnabled);
-
}
build方法中前面幾個if判斷我們剛纔已經說過了,這幾個判斷中的變量我們在創建Picasso實例的時候都可以自定義,也可以使用系統默認創建的,我們再來總結一下:
downloader 創建一個下載器
cache 創建圖片的緩存器,默認使用LruCache,這個我們一般不做修改,最多重新配置一下LruCache
service 創建圖片下載的線程池
transformer 對Request進行轉換,默認不做任何出處理,事實上我們一般也不需要做任何處理。
接下來就是創建一個Stats實例,這個stats主要是用來統計緩存,下載數量等數據,一言以蔽之,就是保存圖片的一些狀態信息。再之後,則是創建一個Dispatcher,創建Dispatcher的時候還傳入了一個HANDLER,這個Handler我們在後文再說,dispatcher顧名思義就是分發,事實上dispatcher主要用來任務調度,這個一會再說,最後new一個Picasso實例返回:
-
Picasso(Context context, Dispatcher dispatcher, Cache cache, Listener listener,
-
RequestTransformer requestTransformer, List<RequestHandler> extraRequestHandlers, Stats stats,
-
Bitmap.Config defaultBitmapConfig, boolean indicatorsEnabled, boolean loggingEnabled) {
-
this.context = context;
-
this.dispatcher = dispatcher;
-
this.cache = cache;
-
this.listener = listener;
-
this.requestTransformer = requestTransformer;
-
this.defaultBitmapConfig = defaultBitmapConfig;
-
-
int builtInHandlers = 7;
-
int extraCount = (extraRequestHandlers != null ? extraRequestHandlers.size() : 0);
-
List<RequestHandler> allRequestHandlers =
-
new ArrayList<RequestHandler>(builtInHandlers + extraCount);
-
-
-
-
-
allRequestHandlers.add(new ResourceRequestHandler(context));
-
if (extraRequestHandlers != null) {
-
allRequestHandlers.addAll(extraRequestHandlers);
-
}
-
allRequestHandlers.add(new ContactsPhotoRequestHandler(context));
-
allRequestHandlers.add(new MediaStoreRequestHandler(context));
-
allRequestHandlers.add(new ContentStreamRequestHandler(context));
-
allRequestHandlers.add(new AssetRequestHandler(context));
-
allRequestHandlers.add(new FileRequestHandler(context));
-
allRequestHandlers.add(new NetworkRequestHandler(dispatcher.downloader, stats));
-
requestHandlers = Collections.unmodifiableList(allRequestHandlers);
-
-
this.stats = stats;
-
this.targetToAction = new WeakHashMap<Object, Action>();
-
this.targetToDeferredRequestCreator = new WeakHashMap<ImageView, DeferredRequestCreator>();
-
this.indicatorsEnabled = indicatorsEnabled;
-
this.loggingEnabled = loggingEnabled;
-
this.referenceQueue = new ReferenceQueue<Object>();
-
this.cleanupThread = new CleanupThread(referenceQueue, HANDLER);
-
this.cleanupThread.start();
-
}
OK,大家看到在Picasso的構造方法裏主要進行了一些變量的初始化,也初始化了RequestHandler,初始化RequestHandler時首先將我們提交進來的requestHandler加入到集合中,然後還往allRequestHandlers中提交了其它的RequestHandler,這些不同的RequestHandler,分別用來處理不同的資源,比如加載相冊的圖片、加載資產文件夾中的圖片、加載網絡圖片等。
OK,那麼到目前爲止,我們所看到的都是build方法中引出的源碼,執行完build之後,我們接下來該做的就是調用load方法了,不管你在load中傳入了什麼,最終都會到達下面這個方法:
-
RequestCreator(Picasso picasso, Uri uri, int resourceId) {
-
if (picasso.shutdown) {
-
throw new IllegalStateException(
-
"Picasso instance already shut down. Cannot submit new requests.");
-
}
-
this.picasso = picasso;
-
this.data = new Request.Builder(uri, resourceId, picasso.defaultBitmapConfig);
-
}
shutdown屬性是判斷Picasso實例是否已經停止運行,如果已經shutdown則拋異常,否則將我們即將要加載的圖片信息保存在data中,data是一個Request.Builder對象,裏邊保存了我們所有的圖片加載的配置信息,比如你調用了centerCrop方法:
-
public RequestCreator centerCrop() {
-
data.centerCrop();
-
return this;
-
}
大家看到這些方法不過都是修改data裏邊的變量,當所有的配置信息都完成之後,接下載就到into方法了,那麼小夥伴們大概也猜到了,真正的圖片加載過程是在into方法中完成的,如下:
-
public void into(ImageView target, Callback callback) {
-
long started = System.nanoTime();
-
checkMain();
-
-
if (target == null) {
-
throw new IllegalArgumentException("Target must not be null.");
-
}
-
-
if (!data.hasImage()) {
-
picasso.cancelRequest(target);
-
if (setPlaceholder) {
-
setPlaceholder(target, getPlaceholderDrawable());
-
}
-
return;
-
}
-
-
if (deferred) {
-
if (data.hasSize()) {
-
throw new IllegalStateException("Fit cannot be used with resize.");
-
}
-
int width = target.getWidth();
-
int height = target.getHeight();
-
if (width == 0 || height == 0) {
-
if (setPlaceholder) {
-
setPlaceholder(target, getPlaceholderDrawable());
-
}
-
picasso.defer(target, new DeferredRequestCreator(this, target, callback));
-
return;
-
}
-
data.resize(width, height);
-
}
-
-
Request request = createRequest(started);
-
String requestKey = createKey(request);
-
-
if (shouldReadFromMemoryCache(memoryPolicy)) {
-
Bitmap bitmap = picasso.quickMemoryCacheCheck(requestKey);
-
if (bitmap != null) {
-
picasso.cancelRequest(target);
-
setBitmap(target, picasso.context, bitmap, MEMORY, noFade, picasso.indicatorsEnabled);
-
if (picasso.loggingEnabled) {
-
log(OWNER_MAIN, VERB_COMPLETED, request.plainId(), "from " + MEMORY);
-
}
-
if (callback != null) {
-
callback.onSuccess();
-
}
-
return;
-
}
-
}
-
-
if (setPlaceholder) {
-
setPlaceholder(target, getPlaceholderDrawable());
-
}
-
-
Action action =
-
new ImageViewAction(picasso, target, request, memoryPolicy, networkPolicy, errorResId,
-
errorDrawable, requestKey, tag, callback, noFade);
-
-
picasso.enqueueAndSubmit(action);
-
}
into方法有點長,但是邏輯還是很清晰,我們來看一下,
首先checkMain方法檢查程序是否運行在主線程,接下來target不能爲空,這個不用多說,簡單。data.hasImage表示是否設置了要加載的圖片資源,如果設置了,則返回true,否則返回false。返回false時進入到if判斷中,這個時候首先取消加載,然後如果設置了佔位圖片,就將其顯示出來。接下來進入到if(deferred)的判斷中,deferred這個變量是在哪裏進行初始化的呢?我們來看看這裏:
-
public RequestCreator fit() {
-
deferred = true;
-
return this;
-
}
-
-
-
RequestCreator unfit() {
-
deferred = false;
-
return this;
-
}
是在我們調用了fit方法的時候,也就是說,如果我們希望我們的圖片在加載的過程中能夠自由縮放以填滿整個ImageView的話,那麼就會進入到這個分支中,進來之後首先是判斷data.hasSize,我們知道這個是判斷圖片是否有寬高,我們來看看hasSize方法:
-
boolean hasSize() {
-
return targetWidth != 0 || targetHeight != 0;
-
}
那麼targetWidth和targetHeight又是在什麼地方調用的呢?我們不由得想到了resize方法:
-
public Builder resize(int targetWidth, int targetHeight) {
-
if (targetWidth < 0) {
-
throw new IllegalArgumentException("Width must be positive number or 0.");
-
}
-
if (targetHeight < 0) {
-
throw new IllegalArgumentException("Height must be positive number or 0.");
-
}
-
if (targetHeight == 0 && targetWidth == 0) {
-
throw new IllegalArgumentException("At least one dimension has to be positive number.");
-
}
-
this.targetWidth = targetWidth;
-
this.targetHeight = targetHeight;
-
return this;
-
}
沒錯,是這裏,那我們在這裏可以得出結論了,如果在加載一張圖片的是否使用了fit這種縮放模式的話,那麼不可以給圖片設置resize屬性,否則會拋一個Fit cannot be used with resize異常,其實這個也很好理解,你設置了fit就是希望圖片自由縮放以便將ImageView填充滿,結果又給圖片設置了固定大小,那麼你到底想怎樣?。接下來系統來獲取ImageView的寬和高,如果ImageView的寬和高爲0的話,則首先把佔位圖片設置上,然後去監聽ImageView的target.getViewTreeObserver().addOnPreDrawListener(this);接口,當ImageView的寬高被賦值之後,繼續加載。否則直接設置ImageView的寬高爲圖片的寬高。OK,以上還都是在做準備工作,一個網絡請求還是沒有發起。接下來我們就要開始構造請求了,在into方法的第33行,我們構建一個請求,接下來是一個shouldReadFromMemoryCache,看名字就知道是否該從內存中讀取圖片,如果是,則根據key從Cache中讀取一張圖片出來,不知道大家是否還記得我們的Cache實際上就是LruCache。
如果從內從中讀取到了圖片,就取消請求,並把圖片設置給ImageView。同時,如果我們設置了回調,則調用回調的onSuccess方法。
接下來55行創建Action,並且將Action添加到一個Picasso的enqueueAndSubmit方法中。接下來我們就來看看這個請求入隊的方法:
-
void enqueueAndSubmit(Action action) {
-
Object target = action.getTarget();
-
if (target != null && targetToAction.get(target) != action) {
-
-
cancelExistingRequest(target);
-
targetToAction.put(target, action);
-
}
-
submit(action);
-
}
首先獲取action裏邊的target,其實就是我們的ImageView,如果這個ImageView不爲空,並且該ImageView已經有了一個Action,則取消已經存在的請求,然後重新給該target設置Action,完了之後就是submit了,我們來看看這個submit:
-
void submit(Action action) {
-
dispatcher.dispatchSubmit(action);
-
}
咦,dispatcher,大家還記不記得我們是在哪裏初始化的dispatcher呢?沒錯,build方法中,這裏調用了dispatcher的dispatchSubmit方法,點擊去再看:
-
void dispatchSubmit(Action action) {
-
handler.sendMessage(handler.obtainMessage(REQUEST_SUBMIT, action));
-
}
哦,原來是使用了Handler,發送了一條消息,那我們來找找handler初始化的地方,在Dispatcher類中,Handler通過如下方式初始化:
-
this.handler = new DispatcherHandler(dispatcherThread.getLooper(), this);
竟然不是new一個Handler,DispatcherHandler是什麼鬼?來看看:
-
private static class DispatcherHandler extends Handler {
-
private final Dispatcher dispatcher;
-
-
public DispatcherHandler(Looper looper, Dispatcher dispatcher) {
-
super(looper);
-
this.dispatcher = dispatcher;
-
}
-
-
@Override public void handleMessage(final Message msg) {
-
switch (msg.what) {
-
case REQUEST_SUBMIT: {
-
Action action = (Action) msg.obj;
-
dispatcher.performSubmit(action);
-
break;
-
}
-
case REQUEST_CANCEL: {
-
Action action = (Action) msg.obj;
-
dispatcher.performCancel(action);
-
break;
-
}
-
case TAG_PAUSE: {
-
Object tag = msg.obj;
-
dispatcher.performPauseTag(tag);
-
break;
-
}
-
case TAG_RESUME: {
-
Object tag = msg.obj;
-
dispatcher.performResumeTag(tag);
-
break;
-
}
-
case HUNTER_COMPLETE: {
-
BitmapHunter hunter = (BitmapHunter) msg.obj;
-
dispatcher.performComplete(hunter);
-
break;
-
}
-
case HUNTER_RETRY: {
-
BitmapHunter hunter = (BitmapHunter) msg.obj;
-
dispatcher.performRetry(hunter);
-
break;
-
}
-
case HUNTER_DECODE_FAILED: {
-
BitmapHunter hunter = (BitmapHunter) msg.obj;
-
dispatcher.performError(hunter, false);
-
break;
-
}
-
case HUNTER_DELAY_NEXT_BATCH: {
-
dispatcher.performBatchComplete();
-
break;
-
}
-
case NETWORK_STATE_CHANGE: {
-
NetworkInfo info = (NetworkInfo) msg.obj;
-
dispatcher.performNetworkStateChange(info);
-
break;
-
}
-
case AIRPLANE_MODE_CHANGE: {
-
dispatcher.performAirplaneModeChange(msg.arg1 == AIRPLANE_MODE_ON);
-
break;
-
}
-
default:
-
Picasso.HANDLER.post(new Runnable() {
-
@Override public void run() {
-
throw new AssertionError("Unknown handler message received: " + msg.what);
-
}
-
});
-
}
-
}
-
}
DispatcherHandler繼承自Handler重寫了它裏邊的方法,順藤摸瓜,找到屬於我們的case,點進去,最終來到了這個方法:
-
void performSubmit(Action action, boolean dismissFailed) {
-
if (pausedTags.contains(action.getTag())) {
-
pausedActions.put(action.getTarget(), action);
-
if (action.getPicasso().loggingEnabled) {
-
log(OWNER_DISPATCHER, VERB_PAUSED, action.request.logId(),
-
"because tag '" + action.getTag() + "' is paused");
-
}
-
return;
-
}
-
-
BitmapHunter hunter = hunterMap.get(action.getKey());
-
if (hunter != null) {
-
hunter.attach(action);
-
return;
-
}
-
-
if (service.isShutdown()) {
-
if (action.getPicasso().loggingEnabled) {
-
log(OWNER_DISPATCHER, VERB_IGNORED, action.request.logId(), "because shut down");
-
}
-
return;
-
}
-
-
hunter = forRequest(action.getPicasso(), this, cache, stats, action);
-
hunter.future = service.submit(hunter);
-
hunterMap.put(action.getKey(), hunter);
-
if (dismissFailed) {
-
failedActions.remove(action.getTarget());
-
}
-
-
if (action.getPicasso().loggingEnabled) {
-
log(OWNER_DISPATCHER, VERB_ENQUEUED, action.request.logId());
-
}
-
}
一進來,首先判斷該請求是否該暫停,接下來關鍵的是24行,調用forRequest方法給hunter賦值,我們來看看這個forRequest方法:
-
static BitmapHunter forRequest(Picasso picasso, Dispatcher dispatcher, Cache cache, Stats stats,
-
Action action) {
-
Request request = action.getRequest();
-
List<RequestHandler> requestHandlers = picasso.getRequestHandlers();
-
-
-
-
for (int i = 0, count = requestHandlers.size(); i < count; i++) {
-
RequestHandler requestHandler = requestHandlers.get(i);
-
if (requestHandler.canHandleRequest(request)) {
-
return new BitmapHunter(picasso, dispatcher, cache, stats, action, requestHandler);
-
}
-
}
-
-
return new BitmapHunter(picasso, dispatcher, cache, stats, action, ERRORING_HANDLER);
-
}
這裏有一個for循環,for循環中的東西就是我們所有的RequestHandler,然後通過一個if來匹配,看使用那個RequestHandler來處理我們的圖片加載。
第25行創建一個BitmapHunter,並在線程池中執行請求,線程池中傳入的對象是hunter,那毫無疑問,hunter肯定是實現了Runnable接口的,那接下來就去看看這個BitmapHunter的run方法:
-
@Override public void run() {
-
try {
-
updateThreadName(data);
-
-
if (picasso.loggingEnabled) {
-
log(OWNER_HUNTER, VERB_EXECUTING, getLogIdsForHunter(this));
-
}
-
-
result = hunt();
-
-
if (result == null) {
-
dispatcher.dispatchFailed(this);
-
} else {
-
dispatcher.dispatchComplete(this);
-
}
-
} catch (Downloader.ResponseException e) {
-
if (!e.localCacheOnly || e.responseCode != 504) {
-
exception = e;
-
}
-
dispatcher.dispatchFailed(this);
-
} catch (NetworkRequestHandler.ContentLengthException e) {
-
exception = e;
-
dispatcher.dispatchRetry(this);
-
} catch (IOException e) {
-
exception = e;
-
dispatcher.dispatchRetry(this);
-
} catch (OutOfMemoryError e) {
-
StringWriter writer = new StringWriter();
-
stats.createSnapshot().dump(new PrintWriter(writer));
-
exception = new RuntimeException(writer.toString(), e);
-
dispatcher.dispatchFailed(this);
-
} catch (Exception e) {
-
exception = e;
-
dispatcher.dispatchFailed(this);
-
} finally {
-
Thread.currentThread().setName(Utils.THREAD_IDLE_NAME);
-
}
-
}
一進來,先更新線程名稱,然後是第9行調用了hunt方法,獲取到一個result,這個result是一個Bitmap,如果獲取到了Bitmap則調用dispatcher.dispatchComplete方法,否則調用dispatcher.dispatchFailed方法,這兩個實際上都是調用了Handler的sendMessage方法,來發送不同的消息做不同處理,我們這裏就來看看hunt()方法,看看這個Bitmap到底是怎麼獲取的:
-
Bitmap hunt() throws IOException {
-
Bitmap bitmap = null;
-
-
if (shouldReadFromMemoryCache(memoryPolicy)) {
-
bitmap = cache.get(key);
-
if (bitmap != null) {
-
stats.dispatchCacheHit();
-
loadedFrom = MEMORY;
-
if (picasso.loggingEnabled) {
-
log(OWNER_HUNTER, VERB_DECODED, data.logId(), "from cache");
-
}
-
return bitmap;
-
}
-
}
-
-
data.networkPolicy = retryCount == 0 ? NetworkPolicy.OFFLINE.index : networkPolicy;
-
RequestHandler.Result result = requestHandler.load(data, networkPolicy);
-
if (result != null) {
-
loadedFrom = result.getLoadedFrom();
-
exifRotation = result.getExifOrientation();
-
-
bitmap = result.getBitmap();
-
-
-
if (bitmap == null) {
-
InputStream is = result.getStream();
-
try {
-
bitmap = decodeStream(is, data);
-
} finally {
-
Utils.closeQuietly(is);
-
}
-
}
-
}
-
-
if (bitmap != null) {
-
if (picasso.loggingEnabled) {
-
log(OWNER_HUNTER, VERB_DECODED, data.logId());
-
}
-
stats.dispatchBitmapDecoded(bitmap);
-
if (data.needsTransformation() || exifRotation != 0) {
-
synchronized (DECODE_LOCK) {
-
if (data.needsMatrixTransform() || exifRotation != 0) {
-
bitmap = transformResult(data, bitmap, exifRotation);
-
if (picasso.loggingEnabled) {
-
log(OWNER_HUNTER, VERB_TRANSFORMED, data.logId());
-
}
-
}
-
if (data.hasCustomTransformations()) {
-
bitmap = applyCustomTransformations(data.transformations, bitmap);
-
if (picasso.loggingEnabled) {
-
log(OWNER_HUNTER, VERB_TRANSFORMED, data.logId(), "from custom transformations");
-
}
-
}
-
}
-
if (bitmap != null) {
-
stats.dispatchBitmapTransformed(bitmap);
-
}
-
}
-
}
-
-
return bitmap;
-
}
首先是判斷是否可以從內存中獲取這張圖片,如果可以,將圖片加載出來並返回,並更新stats中相關變量,否則就會來到第17行,從一個RequestHandler中讀取,那麼RequestHandler是我們在new一個Picasso的時候傳入了多個RequestHandler,這裏到底是使用哪一個RequestHandler呢?這就和我們上文說的匹配RequestHandler有關了,毫無疑問,我們下載網絡圖片,當然是匹配NetworkRequestHandler,那我們看看NetworkRequestHandler裏邊的load方法:
-
@Override public Result load(Request request, int networkPolicy) throws IOException {
-
Response response = downloader.load(request.uri, request.networkPolicy);
-
if (response == null) {
-
return null;
-
}
-
-
Picasso.LoadedFrom loadedFrom = response.cached ? DISK : NETWORK;
-
-
Bitmap bitmap = response.getBitmap();
-
if (bitmap != null) {
-
return new Result(bitmap, loadedFrom);
-
}
-
-
InputStream is = response.getInputStream();
-
if (is == null) {
-
return null;
-
}
-
-
-
if (loadedFrom == DISK && response.getContentLength() == 0) {
-
Utils.closeQuietly(is);
-
throw new ContentLengthException("Received response with 0 content-length header.");
-
}
-
if (loadedFrom == NETWORK && response.getContentLength() > 0) {
-
stats.dispatchDownloadFinished(response.getContentLength());
-
}
-
return new Result(is, loadedFrom);
-
}
這個方法裏首先調用了downloader裏邊的load方法,獲取一個Response對象,然後再拿到這個response對象裏邊的Bitmap返回,downloader就是我們在上文說的那個downloader,我們就看那個源碼吧,反正和Piasso自帶的差不多,看看它裏邊的load方法:
-
@Override
-
public Response load(Uri uri, int networkPolicy) throws IOException {
-
CacheControl cacheControl = null;
-
if (networkPolicy != 0) {
-
if (NetworkPolicy.isOfflineOnly(networkPolicy)) {
-
cacheControl = CacheControl.FORCE_CACHE;
-
} else {
-
CacheControl.Builder builder = new CacheControl.Builder();
-
if (!NetworkPolicy.shouldReadFromDiskCache(networkPolicy)) {
-
builder.noCache();
-
}
-
if (!NetworkPolicy.shouldWriteToDiskCache(networkPolicy)) {
-
builder.noStore();
-
}
-
cacheControl = builder.build();
-
}
-
}
-
-
Request.Builder builder = new Request.Builder().url(uri.toString());
-
if (cacheControl != null) {
-
builder.cacheControl(cacheControl);
-
}
-
-
okhttp3.Response response = client.newCall(builder.build()).execute();
-
int responseCode = response.code();
-
if (responseCode >= 300) {
-
response.body().close();
-
throw new ResponseException(responseCode + " " + response.message(), networkPolicy,
-
responseCode);
-
}
-
-
boolean fromCache = response.cacheResponse() != null;
-
-
ResponseBody responseBody = response.body();
-
return new Response(responseBody.byteStream(), fromCache, responseBody.contentLength());
-
}
哈哈,在這裏我們總算看到了網絡訪問的代碼了,就是大家熟悉的OkHttp網絡請求了,下載到數據之後,再重新new一個Response對象返回。just so so。。。。
現在我們再回到BitmapHunter的run方法中,當成功獲取到bitmap之後,接下來調用dispatcher.dispatchComplete(this);發送一條消息:
-
void dispatchComplete(BitmapHunter hunter) {
-
handler.sendMessage(handler.obtainMessage(HUNTER_COMPLETE, hunter));
-
}
又是Handler,再找:
-
case HUNTER_COMPLETE: {
-
BitmapHunter hunter = (BitmapHunter) msg.obj;
-
dispatcher.performComplete(hunter);
-
break;
-
}
這裏又調用了dispatcher.performComplete方法,點擊去看看:
-
void performComplete(BitmapHunter hunter) {
-
if (shouldWriteToMemoryCache(hunter.getMemoryPolicy())) {
-
cache.set(hunter.getKey(), hunter.getResult());
-
}
-
hunterMap.remove(hunter.getKey());
-
batch(hunter);
-
if (hunter.getPicasso().loggingEnabled) {
-
log(OWNER_DISPATCHER, VERB_BATCHED, getLogIdsForHunter(hunter), "for completion");
-
}
-
}
首先判斷了是否該將Bitmap寫入到內存緩存中,需要的話就寫入,然後是batch方法:
-
private void batch(BitmapHunter hunter) {
-
if (hunter.isCancelled()) {
-
return;
-
}
-
batch.add(hunter);
-
if (!handler.hasMessages(HUNTER_DELAY_NEXT_BATCH)) {
-
handler.sendEmptyMessageDelayed(HUNTER_DELAY_NEXT_BATCH, BATCH_DELAY);
-
}
-
}
首先判斷如果hunter已經被取消,則直接返回,否則將hunter加入到batch中,然後判斷Handler中是否有一條HUNTER_DELAY_NEXT_BATCH消息,沒有的話就發一條,OK,發一條之後,我們來找到相關的case:
-
case HUNTER_DELAY_NEXT_BATCH: {
-
dispatcher.performBatchComplete();
-
break;
-
}
繼續點:
-
void performBatchComplete() {
-
List<BitmapHunter> copy = new ArrayList<BitmapHunter>(batch);
-
batch.clear();
-
mainThreadHandler.sendMessage(mainThreadHandler.obtainMessage(HUNTER_BATCH_COMPLETE, copy));
-
logBatch(copy);
-
}
在這裏將batch存入到一個新的List集合中,然後mainThreadHandler又發送一條消息,這個mainThreadHandler是什麼鬼?不知道大家是否還記得在build方法中我們創建Dispatch實例的時候傳入了一個Handler,就是那個在主線程中創建的Handler,在Picasso那個類裏邊,我們找到了HUNTER_BATCH_COMPLETE這個case:
-
case HUNTER_BATCH_COMPLETE: {
-
@SuppressWarnings("unchecked") List<BitmapHunter> batch = (List<BitmapHunter>) msg.obj;
-
-
for (int i = 0, n = batch.size(); i < n; i++) {
-
BitmapHunter hunter = batch.get(i);
-
hunter.picasso.complete(hunter);
-
}
-
break;
-
}
這個case中我們來一條一條的處理batch中的消息,交給picasso的complete方法去處理:
-
void complete(BitmapHunter hunter) {
-
Action single = hunter.getAction();
-
List<Action> joined = hunter.getActions();
-
-
boolean hasMultiple = joined != null && !joined.isEmpty();
-
boolean shouldDeliver = single != null || hasMultiple;
-
-
if (!shouldDeliver) {
-
return;
-
}
-
-
Uri uri = hunter.getData().uri;
-
Exception exception = hunter.getException();
-
Bitmap result = hunter.getResult();
-
LoadedFrom from = hunter.getLoadedFrom();
-
-
if (single != null) {
-
deliverAction(result, from, single);
-
}
-
-
if (hasMultiple) {
-
-
for (int i = 0, n = joined.size(); i < n; i++) {
-
Action join = joined.get(i);
-
deliverAction(result, from, join);
-
}
-
}
-
-
if (listener != null && exception != null) {
-
listener.onImageLoadFailed(this, uri, exception);
-
}
-
}
在這裏,14行我們拿到Bitmap,17行去派發Action,如果有合併的Action則在25行進行派發,我們來看看這個派發操作:
-
private void deliverAction(Bitmap result, LoadedFrom from, Action action) {
-
if (action.isCancelled()) {
-
return;
-
}
-
if (!action.willReplay()) {
-
targetToAction.remove(action.getTarget());
-
}
-
if (result != null) {
-
if (from == null) {
-
throw new AssertionError("LoadedFrom cannot be null.");
-
}
-
action.complete(result, from);
-
if (loggingEnabled) {
-
log(OWNER_MAIN, VERB_COMPLETED, action.request.logId(), "from " + from);
-
}
-
} else {
-
action.error();
-
if (loggingEnabled) {
-
log(OWNER_MAIN, VERB_ERRORED, action.request.logId());
-
}
-
}
-
}
第8行,如果Bitmap不爲空,則會執行第12行,調用action的complete方法,Action是我們在into方法中創建的,當時new了一個ImageViewAction,所以我們去找ImageViewAction的complete方法:
-
@Override public void complete(Bitmap result, Picasso.LoadedFrom from) {
-
if (result == null) {
-
throw new AssertionError(
-
String.format("Attempted to complete action with no result!\n%s", this));
-
}
-
-
ImageView target = this.target.get();
-
if (target == null) {
-
return;
-
}
-
-
Context context = picasso.context;
-
boolean indicatorsEnabled = picasso.indicatorsEnabled;
-
PicassoDrawable.setBitmap(target, context, result, from, noFade, indicatorsEnabled);
-
-
if (callback != null) {
-
callback.onSuccess();
-
}
-
}
獲取到所有信息之後,然後調用PicassoDrawable的setBitmap方法:
-
static void setBitmap(ImageView target, Context context, Bitmap bitmap,
-
Picasso.LoadedFrom loadedFrom, boolean noFade, boolean debugging) {
-
Drawable placeholder = target.getDrawable();
-
if (placeholder instanceof AnimationDrawable) {
-
((AnimationDrawable) placeholder).stop();
-
}
-
PicassoDrawable drawable =
-
new PicassoDrawable(context, bitmap, placeholder, loadedFrom, noFade, debugging);
-
target.setImageDrawable(drawable);
-
}
終於看到了給target設置圖片的代碼了,這裏的代碼都很簡單,不多說。
OK,這就是對Picasso做了一個簡單介紹,有問題的小夥伴歡迎留言討論。
以上。
參考資料
1.http://blog.csdn.net/zxm317122667/article/details/51814095
2.http://www.jianshu.com/p/c2b029f69f52