android使用多線程更新ui示例分享

Android線程涉及的技術有：Handler;Message;MessageQueue;Looper;HandlerThread。

下面看一段在線程中更新UI的代碼：
復制代碼 代碼如下:
public class MainActivity extends Activity {
private TextView timeLable;
private Button stopBtn;
private Thread mThread;
private boolean isRunning = true;
private int timeCount = 0;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    timeLable = (TextView) findViewById(R.id.timelable);
    stopBtn = (Button) findViewById(R.id.stop);
    stopBtn.setOnClickListener(new OnClickListener() {

        @Override
        public void onClick(View v) {              
            isRunning = false;
        }
    });

    mThread = new Thread(new Runnable() {

        @Override
        public void run() {
            while (isRunning) {
                try {
                    Thread.sleep(1000);
                    timeCount++;
                    timeLable.setText("timeCount=" + timeCount + " 秒");
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }

        }
    });
    mThread.start();       
}
}

這段代碼只是在線程中更新TextView的顯示內容，但是執行後看不到效果，並且報了一個錯：android.view.ViewRootImpl$CalledFromWrongThreadException: Only the original thread that created a view hierarchy can touch its views.
在Android中更新UI處理必須由創建它的線程更新，而不能在其他線程中更新。上面的錯誤原因就在於此。

由於timeLable是一個UI控件，它是在主線程中創建的，但是它卻在子線程中被更新了，更新操作在mThread線程的run()方法中實現。這樣的處理違背了Android多線程編程規則，系統會拋出異常。

要解決這個問題，就要明確主線程和子線程的職責。主線程的職責是創建、顯示和更新UI控件、處理UI事件、啟動子線程、停止子線程等;子線程的職責是計算時間和向主線程發出更新UI消息，而不是直接更新UI。子線程向主線程發送消息可以用Handler實現。代碼如下：

復制代碼 代碼如下:
public class MainActivity extends Activity {

private TextView timeLable;
private Button stopBtn;
private Thread mThread;
private boolean isRunning = true;
private int timeCount = 0;

final private Handler mHandler = new Handler(){
    public void handleMessage(Message msg) {
        switch (msg.what) {
        case 0 :
            timeLable.setText("timeCount=" + timeCount + " 秒");
            break;
        default :
            break;
        }
    }
};

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    timeLable = (TextView) findViewById(R.id.timelable);
    stopBtn = (Button) findViewById(R.id.stop);
    stopBtn.setOnClickListener(new OnClickListener() {

        @Override
        public void onClick(View v) {

            isRunning = false;
        }
    });

    mThread = new Thread(new Runnable() {

        @Override
        public void run() {
            while (isRunning) {
                try {
                    Thread.sleep(1000);
                    timeCount++;
                    mHandler.sendEmptyMessage(0);
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }

        }
    });
    mThread.start();
}
}

運行後不會報之前的錯，TextView也能正常更新內容了。