文章標題

Handler的學習

最簡單的handleMode

 @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        button = (Button) findViewById(R.id.button);
        text = (TextView) findViewById(R.id.tv_tv);

        final Handler handler = new Handler(){
            @Override
            public void handleMessage(Message msg) {
                super.handleMessage(msg);

                if(msg.what == 1001){
                    //消息發送過來了 更改UI
                    text.setText("在handler裏面更改成功");
                }
            }
        };

        button.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                new Thread(new Runnable() {
                    @Override
                    public void run() {
                        //用handler發送一個空消息，攜帶一個what參數
                        handler.sendEmptyMessage(1001);
                    }
                }).start();
            }
        });
    }

Handler常見發送消息方法

Message.obtain();//這裏可以獲取到一個Message對象而不用new出來,因爲在下層它有個緩存池,如果沒有創建，那麼會自動創建一個Message對象回來。

handler.sendEmptyMessage(1001);
Message message = Message.obtain();//這裏可以獲取到一個Message對象
message.what = 1000;
message.arg1 = 1001;
message.arg2 = 1002; //arg 存儲int值
message.obj = MainActivity.this;//存儲一個對象
handler.sendMessageAtTime(message, SystemClock.uptimeMillis() + 3000);//延遲系統時間+3秒發送消息
handler.sendMessageDelayed(message, 3000);//延遲絕對時間 3秒發送消息
//handler.post(new Runnable(run))

小程序，下載文件，界面的progressbar用Handler來發送消息實時更新進度

package com.example.synnection.handlermode;

import android.nfc.Tag;
import android.os.Bundle;
import android.os.Environment;
import android.os.Handler;
import android.os.Message;
import android.support.v7.app.AppCompatActivity;
import android.util.Log;
import android.view.View;
import android.widget.ProgressBar;

import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.URL;

public class DwonLoadDemo extends AppCompatActivity {
    private static final String APP_URL =  "http://download.sj.qq.com/upload/connAssitantDownload/upload/MobileAssistant_1.apk";;
    private static final String TAG ="DownLoadDemoActivity";
    private ProgressBar progressBar ;
     /*
        異步下載文件更新進度條的步驟
        主線程
        點擊按鍵
        發起下載
        開啓子線程下載
        下載完成後通知主線程
        主線程更新進度條
         */

    Handler handler = new Handler(){
        @Override
        public void handleMessage(Message msg) {

           if (msg.what ==100){

               int currentPro = msg.arg1;
               progressBar.setProgress(currentPro);
               Log.i(TAG,"更新進度條ing");
           }

        }
    };

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_download);
         progressBar = (ProgressBar) findViewById(R.id.progressBar);

        findViewById(R.id.button2).setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                // 下載文件
                downLoad(APP_URL);
            }
        });
    }

    private void downLoad(final String appUrl) {
        //創建下載路徑
        // Environment.getExternalStorageDirectory() 獲取擴展存儲設備的資源路徑
        String downLoadFolderName = Environment.getExternalStorageDirectory() + File.separator + "123" + File.separator;
        //創建文件夾
        File file = new File(downLoadFolderName);
        //判斷文件夾是否存在,不存在則創建
        if(!file.exists()){
            file.mkdir();
        }
        //創建文件名
        final File appFile = new File(downLoadFolderName+"hello.apk");
        //判斷文件是否存在,如存在則刪除
        if(appFile.exists()){
            appFile.delete();
            Log.i(TAG,"刪除成功");
        }
        if(appFile!=null){
            Log.i(TAG,"文件創建成功");
        }
        /**
         *  在子線程中下載文件
         */
        new Thread(new Runnable(){
            @Override
            public void run() {
                try {
                    URL url = new URL(appUrl);
                    HttpURLConnection conn = (HttpURLConnection) url.openConnection();
                    int fileMaxLength = conn.getContentLength();//獲取文件的總長度
                    InputStream is =  conn.getInputStream();//獲取輸入流
                    byte[] b = new byte[1024*1024 ];//每次讀取大小
                    int len = 0;//當前的長度
                    int currentDwonLoadLen = 0;
                    OutputStream os = new FileOutputStream(appFile);//寫入appFile文件中
                    while ((len =is.read(b)) != -1){
                        //每次寫入b,從下標0,寫到len
                        os.write(b,0,len);
                        //當前下載的大小
                        currentDwonLoadLen += len;
                        //當前進度條的長度
                        int currentprogress = currentDwonLoadLen*100 /fileMaxLength;
                        Log.i(TAG,"currentprogress="+currentprogress);
                        //獲取Message對象 發送消息通知UI更新進度條
                        Message message = handler.obtainMessage();
                        message.what = 100;
                        message.arg1 = currentprogress;
                        handler.sendMessage(message);
                         //關閉流
                        os.close();
                        is.close();
                    }
                } catch (MalformedURLException e) {
                    e.printStackTrace();
                } catch (IOException e) {
                    e.printStackTrace();
                }

            }
        }).start();
    }

}

做完出現過幾個問題。一個讀寫 網絡 權限沒加
一個anr 一點擊按鈕卡死。
因爲把    Message message = handler.obtainMessage();放在了子線程外面也就是在while循環外面
每次發送消息都用的同一個message 導致程序anr卡死
講道理，放while循環裏面每次調用的也是同一個message對象，因爲下層是用了一個緩存池來保存的，那爲什麼放外面會anr呢？
暫時沒理解

小程序用Handler實現倒計時

public class CountDownTime extends AppCompatActivity {
    //倒計時間隔
    public static final int COUNT_OUT = 2000;
    //倒計時的標記
    public static final int COUNT_OUT_FLAG = 1001;
    //倒計時初始值
    public static final int COUNT_OUT_MAX = 10;
    /**
     * 使用Handler倒計時
     * 創建Handler
     * 發送消息,改變textview值
     */
    private TextView mCountDownTextView;
    //發送一個延遲消息讓handler處理更新Ui//有可能會內存泄漏
 //   Handler handler = new Handler(){
//        @Override
  //      public void handleMessage(Message msg) {
 //           super.handleMessage(msg);
            //mCountDownTextView.setText(String.valueOf(COUNT_OUT_MAX //-1));

 //       }
 //   };

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_countdown);
        mCountDownTextView = (TextView) findViewById(R.id.tv_countdwon);

        //獲取一個消息實例
        Message message = handler.obtainMessage();
        message.what = COUNT_OUT_FLAG;
        message.arg1 = COUNT_OUT;
        //發送消息到handlerMessage裏處理
        handler.sendMessageDelayed(message,2000);

    }
}

問題：上面的Handler有可能會造成內存泄漏，因爲這裏的Handler持有Activity的強引用，有可能此Activity被銷燬了，這裏的Handler還是持有引用。
解決：
讓這裏的Handler實例變爲static靜態的，然後再讓Handler持有該Activity的弱引用，在該Activity銷燬時，該Handler也一同銷燬。

public class CountDownTime extends AppCompatActivity {
    //倒計時間隔
    public static final int COUNT_OUT = 2000;
    //倒計時的標記
    public static final int COUNT_OUT_FLAG = 1001;
    //倒計時初始值
    public static final int COUNT_OUT_MAX = 10;
    //記錄當前倒數最小值
    public static int countMin = COUNT_OUT_MAX;
    private MyWeakHandler handler;
    /**
     * 使用Handler倒計時
     * 創建Handler
     * 發送消息,改變textview值
     */
    private TextView mCountDownTextView;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_countdown);
        mCountDownTextView = (TextView) findViewById(R.id.tv_countdwon);
        //獲取一個消息實例
        handler = new MyWeakHandler(CountDownTime.this);
        Message message = handler.obtainMessage();
        message.what = COUNT_OUT_FLAG;
        message.arg1 = COUNT_OUT_MAX;
        //發送消息到handlerMessage裏處理
        handler.sendMessage(message);
    }

    /**
     * 自定義一個類 繼承Handler 實現Handler的弱引用
     */
    private static class MyWeakHandler extends Handler {
        CountDownTime mActivity;
        MyWeakHandler(CountDownTime activity) {
            //創建弱引用的實例
            WeakReference weakReference = new WeakReference<>(activity);
            //獲取當前弱引用對應的上下文
            mActivity = (CountDownTime) weakReference.get();
        }

        //重寫handlerMessage方法 實現倒計時
        @Override
        public void handleMessage(Message msg) {
            //處理髮送過來的消息,
            if (msg.what == COUNT_OUT_FLAG) {
                //拿到外部類控件 更改值
                mActivity.mCountDownTextView.setText(String.valueOf(countMin));
                //循環倒計時數字爲0，否則再次發送延遲消息更新UI
                if (countMin > 0) {
                    Message message = mActivity.handler.obtainMessage();
                    message.what = COUNT_OUT_FLAG;
                    countMin = countMin - 1;
                    mActivity.handler.sendMessageDelayed(message, COUNT_OUT);
                }
            }
        }
    }

用Handler來實現打地鼠的小程序

public class Diglett extends AppCompatActivity {
    public static final String TAG = "diglett";
    public static final int RANDOM_TOME = 1000;
    public static final int Flag = 1009;
    public int mRandomTime =2000;
    public int mRandomPosition =0;
    public int mClickNumber = 0;
    public static final int MAX_COUNT= 10;
    private DigletttHandler mHandler;
    /**
     * 打地鼠遊戲:
     * 創建一個二位數組代表隨即的地鼠xy位置
     * 點擊地鼠圖片後隱藏圖片，發送延遲消息 更換圖片的位置 顯示圖片 同時記錄打到地鼠的最大數目
     */

    private TextView mTextView;
    private Button mStartGame;

    private ImageView mImageView;
    //代表地鼠將要出現的位置 一維x軸座標 二維y軸座標
    private int[][] mPositions = new int[][] {
            {123,323},{142,245},
            {323,123},{52,382},
            {323,155},{32,85},
            {223,223},{242,45},
            {379,146},{442,55}
    };

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_diglett);
        initView();
        initData();
        initListener();
    }

    private void initView() {
        mTextView = (TextView) findViewById(R.id.text_view);
        mStartGame = (Button) findViewById(R.id.start_game);
        mImageView = (ImageView) findViewById(R.id.imageView);
    }

    private void initData() {
        mHandler = new DigletttHandler(Diglett.this);
        Log.i(TAG,"mposition = "+mPositions.length);
    }
    private void initListener(){
        mStartGame.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Log.i(TAG,"開始遊戲111");
                //開始打地鼠
                start(mRandomTime);
                mStartGame.setVisibility(View.GONE);
                mTextView.setVisibility(View.VISIBLE);
                Log.i(TAG,"開始遊戲222");
            }
        });

        mImageView.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                //只有點擊過圖片才自增
                mClickNumber++;
                mImageView.setX(mPositions[mRandomPosition][0]);
                mImageView.setY(mPositions[mRandomPosition][1]);
                mImageView.setVisibility(View.VISIBLE);
                //同時更改TextView顯示打了多少個地鼠
                mTextView.setText("打了"+mClickNumber+"只地鼠");
                next(mRandomTime);
            }
        });
    }



    /**
     *  開始打地鼠,顯示地鼠 給個隨即地址 把Button隱藏
     */
    private void start(int delayed) {
        mImageView.setX(mPositions[0][mRandomPosition]);
        mImageView.setY(mPositions[1][mRandomPosition]);
        mImageView.setVisibility(View.VISIBLE);
        //發送延遲消息
        Message message = mHandler.obtainMessage();
        mHandler.sendMessageDelayed(message,delayed);

    }
    Random random ;
    private void next(int delayed) {
        if(random ==null){
            random = new Random();
        }
        mRandomTime = random.nextInt(RANDOM_TOME)+ RANDOM_TOME;
        //顯示地鼠，隨即生成一個位置，判斷是否打到最大數目 否則一直循環發送延遲消息
        if(mClickNumber<MAX_COUNT){
            //發送消息
            Message message = mHandler.obtainMessage();
            message.what = Flag;
            message.arg1 = random.nextInt(10);
            mHandler.sendMessageDelayed(message,delayed);

        }else{
            //重新開始遊戲按鈕
            mStartGame.setVisibility(View.VISIBLE);
            //重置當前打過多少地鼠
            mClickNumber = 0;
            mImageView.setVisibility(View.GONE);
            mTextView.setText("很棒，打完拉，點擊重新開始遊戲");
            return;

        }
    }

     static class DigletttHandler extends Handler{
        WeakReference weakReference ;
         public DigletttHandler(Diglett activity) {
             weakReference = new WeakReference<>(activity);
         }

         @Override
         public void handleMessage(Message msg) {
             super.handleMessage(msg);
             //獲取當前的上下文
             Diglett mActivity = (Diglett) weakReference.get();
             //處理開始遊戲的消息, 未點擊地鼠的話,同樣執行next()。不記錄當前點擊的數量
             Log.i(TAG,"clickNumber = "+mActivity.mClickNumber);

             if(msg.what == Flag){
                 int position  =msg.arg1 ;
                 mActivity.mImageView.setX(mActivity.mPositions[position][0]);
                 mActivity.mImageView.setY(mActivity.mPositions[position][1])
                 ;mActivity.next(mActivity.mRandomTime);
             }
         }
     }
}
還有幾個問題沒解決，地鼠打完消息還在發送，打地鼠的時候，越打速度越快，等幾天修改。

數據存儲的學習

GirdView的學習

踩過的一些坑。

AsyncTask的學習

studio的一些坑？

https://yachay.unat.edu.pe/blog/index.php?comment_area=format_blog&comment_component=blog&comment_co

linux以太網驅動總結