android使用多线程更新ui示例分享

Android线程涉及的技术有：Handler;Message;MessageQueue;Looper;HandlerThread。

下面看一段在线程中更新UI的代码：

复制代码 代码如下:

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();       
}
}

这段代码只是在线程中更新TextView的显示内容，但是执行后看不到效果，并且报了一个错：android.view.ViewRootImpl$CalledFromWrongThreadException: Only the original thread that created a view hierarchy can touch its views.
在Android中更新UI处理必须由创建它的线程更新，而不能在其他线程中更新。上面的错误原因就在于此。

由于timeLable是一个UI控件，它是在主线程中创建的，但是它却在子线程中被更新了，更新操作在mThread线程的run()方法中实现。这样的处理违背了Android多线程编程规则，系统会抛出异常。

要解决这个问题，就要明确主线程和子线程的职责。主线程的职责是创建、显示和更新UI控件、处理UI事件、启动子线程、停止子线程等;子线程的职责是计算时间和向主线程发出更新UI消息，而不是直接更新UI。子线程向主线程发送消息可以用Handler实现。代码如下：

复制代码 代码如下:

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();
}
}

运行后不会报之前的错，TextView也能正常更新内容了。