Android Handler机制_android端handler机制-优快云博客

转载出处：http://www.open-open.com/lib/view/open1338942421672.html

直接在UI线程中开启子线程来更新TextView显示的内容，运行程序我们会发现，如下错误：android.view.ViewRoot$CalledFromWrongThreadException: Only the original thread that created a view hierarchy can touch its views.翻译过来就是：只有创建这个控件的线程才能去更新该控件的内容。

所有的UI线程要去负责View的创建并且维护它，例如更新冒个TextView的显示，都必须在主线程中去做，我们不能直接在UI线程中去创建子线程，要利用消息机制：handler，如下就是handler的简单工作原理图：

既然android给我们提供了Handler机制来解决这样的问题，请看如下代码：

public class HandlerTestActivity extends Activity {
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    private TextView tv;
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    private static final int UPDATE = 0;
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    private Handler handler = new Handler() {
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        @Override
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        public void handleMessage(Message msg) {
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            // TODO 接收消息并且去更新UI线程上的控件内容
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            if (msg.what == UPDATE) {
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                // Bundle b = msg.getData();
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                // tv.setText(b.getString("num"));
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                tv.setText(String.valueOf(msg.obj));
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            }
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            super.handleMessage(msg);
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        }
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    };
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    /** Called when the activity is first created. */
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    @Override
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    public void onCreate(Bundle savedInstanceState) {
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        super.onCreate(savedInstanceState);
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        setContentView(R.layout.main);
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        tv = (TextView) findViewById(R.id.tv);
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        new Thread() {
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            @Override
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            public void run() {
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                // TODO 子线程中通过handler发送消息给handler接收，由handler去更新TextView的值
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                try {
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                    for (int i = 0; i < 100; i++) {
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                        Thread.sleep(500);
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                        Message msg = new Message();
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                        msg.what = UPDATE;
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                        // Bundle b = new Bundle();
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                        // b.putString("num", "更新后的值：" + i);
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                        // msg.setData(b);
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                        msg.obj = "更新后的值：" + i;
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                        handler.sendMessage(msg);
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                    }
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                } catch (InterruptedException e) {
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                    e.printStackTrace();
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                }
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            }
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        }.start();
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    }
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}