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：
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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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|
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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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|
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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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|
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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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|
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} |
我们就通过Handler机制来处理了子线程去更新UI线程控件问题，Andrid开发中要经常用到这种机制。
