直接在UI線程中開啟子線程來更新TextView顯示的內容，運行程序我們會發現，如下錯 誤：android.view.ViewRoot$CalledFromWrongThreadException: Only the original thread that created a view hierarchy can touch its views.翻譯過來就是：只有創建這個控件的線程才能去更新該控件的內容。

所有的UI線程要去負責View的創建并且維護它，例如更新冒個TextView的顯示，都必須在主線程中去做，我們不能直接在UI線程中去創建子線程，要利用消息機制：handler，如下就是handler的簡單工作原理圖：

既然android給我們提供了Handler機制來解決這樣的問題，請看如下代碼：

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

????????我們就通過Handler機制來處理了子線程去更新UI線程控件問題，Andrid開發中要經常用到這種機制。

轉載于:https://www.cnblogs.com/pinksnow520/p/4101032.html

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