Launcher源碼中Intent.createChooser()實現原理及小例子

 在上一篇中，簡單的分析了一下源代碼，在

final Intent pickWallpaper = new Intent(Intent.ACTION_SET_WALLPAPER);
        Intent chooser = Intent.createChooser(pickWallpaper,
                getText(R.string.chooser_wallpaper));

final Intent pickWallpaper = new Intent(Intent.ACTION_SET_WALLPAPER); Intent chooser = Intent.createChooser(pickWallpaper, getText(R.string.chooser_wallpaper));

處百思不得其解，後來在網上找，也沒有很透徹的解釋。先看下它的官方文檔吧：

public static Intent createChooser (Intent target, CharSequence title)
Since: API Level 1

Convenience function for creating a ACTION_CHOOSER Intent.
Parameters
target  The Intent that the user will be selecting an activity to perform.
title   Optional title that will be displayed in the chooser.
Returns

    * Return a new Intent object that you can hand to Context.startActivity() and related methods.

public static Intent createChooser (Intent target, CharSequence title) Since: API Level 1 Convenience function for creating a ACTION_CHOOSER Intent. Parameters target The Intent that the user will be selecting an activity to perform. title Optional title that will be displayed in the chooser. Returns * Return a new Intent object that you can hand to Context.startActivity() and related methods.

在google上面也找了下，慢慢的有些明白，在一篇文章中看到這麼一段話：

這裏是要找到所有能處理Intent.ACTION_SET_WALLPAPER請求的activity，其字符串表示爲android.intent.action.SET_WALLPAPER。使用Eclipse搜索之後，在以下應用的AndroidManifest.xml文件都找到了能處理這個請求的activity：
packages/apps/Gallery
packages/apps/Launcher2
packages/wallpapers/LivePicker
再看看下面的這個圖：


壁紙對應的是Launcher2裏面的WallpaperChooser.activity。動態壁紙對應的是packages/wallpapers/LivePicker的LiveWallpaperListActivity，他們的共同點 就是在AndroidManifest.xml都有

<intent-filter>
               <action android:name="android.intent.action.SET_WALLPAPER" />
               <category android:name="android.intent.category.DEFAULT" />
           </intent-filter>

<intent-filter> <action android:name="android.intent.action.SET_WALLPAPER" /> <category android:name="android.intent.category.DEFAULT" /> </intent-filter>
如下定義，或許你有了些許明白，看下http://groups.google.com/group/android-developers/browse_thread/thread/9d376a94066057a4這裏面的解釋，我英語不是太好，按照我自己的理解就是，你如果像下面這樣

Intent pickWallpaper = new Intent(Intent.ACTION_SET_WALLPAPER);
        Intent chooser = Intent.createChooser(pickWallpaper,

Intent pickWallpaper = new Intent(Intent.ACTION_SET_WALLPAPER); Intent chooser = Intent.createChooser(pickWallpaper,建立一個intent chooser，系統會尋找所有activity，然後把有

<intent-filter>
               <action android:name="android.intent.action.SET_WALLPAPER" />
               <category android:name="android.intent.category.DEFAULT" />
           </intent-filter>

<intent-filter> <action android:name="android.intent.action.SET_WALLPAPER" /> <category android:name="android.intent.category.DEFAULT" /> </intent-filter>定義的activity形成列表提供給使用者。爲了驗證我的想法，個人寫了一個很簡單的小例子，MainActivity代碼如下：

public class MainActivity extends Activity {
    /** Called when the activity is first created. */
private Button button;
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);

        button=(Button)findViewById(R.id.wallpaperButton);
        button.setOnClickListener(new View.OnClickListener() {

@Override
public void onClick(View v) {
// TODO Auto-generated method stub
final Intent pickWallpaper = new Intent(Intent.ACTION_SET_WALLPAPER);
       Intent chooser = Intent.createChooser(pickWallpaper,"tese the ACTION_SET_WALLPAPER");
       startActivity(chooser);
}
});
    }
}

public class MainActivity extends Activity { /** Called when the activity is first created. */ private Button button; @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); button=(Button)findViewById(R.id.wallpaperButton); button.setOnClickListener(new View.OnClickListener() { @Override public void onClick(View v) { // TODO Auto-generated method stub final Intent pickWallpaper = new Intent(Intent.ACTION_SET_WALLPAPER); Intent chooser = Intent.createChooser(pickWallpaper,"tese the ACTION_SET_WALLPAPER"); startActivity(chooser); } }); } }還有一個demo，代碼如下

public class Demo extends Activity {


@Override
protected void onCreate(Bundle savedInstanceState) {
// TODO Auto-generated method stub
super.onCreate(savedInstanceState);
setContentView(R.layout.demo);
}
}

public class Demo extends Activity { @Override protected void onCreate(Bundle savedInstanceState) { // TODO Auto-generated method stub super.onCreate(savedInstanceState); setContentView(R.layout.demo); } }
demo.xml文件裏面只有一個textview很簡單。
然後是AndroidManifest.xml文件：

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
      package="cn.demo"
      android:versionCode="1"
      android:versionName="1.0">




    <application android:icon="@drawable/icon" android:label="@string/app_name">
        <activity android:name=".MainActivity"
                  android:label="@string/app_name">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />
                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>

<?xml version="1.0" encoding="utf-8"?> <manifest xmlns:android="http://schemas.android.com/apk/res/android" package="cn.demo" android:versionCode="1" android:versionName="1.0"> <application android:icon="@drawable/icon" android:label="@string/app_name"> <activity android:name=".MainActivity" android:label="@string/app_name"> <intent-filter> <action android:name="android.intent.action.MAIN" /> <category android:name="android.intent.category.LAUNCHER" /> </intent-filter> </activity>

<activity android:name=".Demo">

<activity android:name=".Demo">

<intent-filter>

<intent-filter>

            <action android:name="android.intent.action.SET_WALLPAPER" />
            <category android:name="android.intent.category.DEFAULT" />
        </intent-filter>
    </activity>
</application>
/manifest>

<action android:name="android.intent.action.SET_WALLPAPER" /> <category android:name="android.intent.category.DEFAULT" /> </intent-filter> </activity> </application> </manifest>


注意：
 

</activity>
<activity android:name=".Demo">
<intent-filter>
                <action android:name="android.intent.action.SET_WALLPAPER" />
                <category android:name="android.intent.category.DEFAULT" />
            </intent-filter>
        </activity>

</activity> <activity android:name=".Demo"> <intent-filter> <action android:name="android.intent.action.SET_WALLPAPER" /> <category android:name="android.intent.category.DEFAULT" /> </intent-filter> </activity>

我在這裏面加了intent適配器 
<action android:name="android.intent.action.SET_WALLPAPER" />


運行下程序，點擊button按鈕，效果如下：

我這個網速太不給力了，弄的心煩意燥，大家看到我自己寫的demo在圖片中得到了顯示，這也是在上一篇 http://blog.csdn.net/aomandeshangxiao/article/details/6767423中給大家看的圖片，爲什麼我的選項多了一個。說到這裏，想必大家都明白了這個原理了，中秋節還有幾分鐘就要到了，祝福大家中秋愉快。

上面所說的簡單的小例子下載地址：http://download.csdn.net/detail/aomandeshangxiao/3593740