Android中的Handler机制

来源：互联网发布：叶萝莉娃娃淘宝编辑：程序博客网时间：2024/05/18 17:42

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 {    private TextView tv;    private static final int UPDATE = 0;    private Handler handler = new Handler() {         @Override        public void handleMessage(Message msg) {            // TODO \u63A5\u6536\u6D88\u606F\u5E76\u4E14\u53BB\u66F4\u65B0UI\u7EBF\u7A0B\u4E0A\u7684\u63A7\u4EF6\u5185\u5BB9            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 \u5B50\u7EBF\u7A0B\u4E2D\u901A\u8FC7handler\u53D1\u9001\u6D88\u606F\u7ED9handler\u63A5\u6536\uFF0C\u7531handler\u53BB\u66F4\u65B0TextView\u7684\u503C                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", "\u66F4\u65B0\u540E\u7684\u503C\uFF1A" + i);                        // msg.setData(b);                        msg.obj = "\u66F4\u65B0\u540E\u7684\u503C\uFF1A" + i;                        handler.sendMessage(msg);                    }                } catch (InterruptedException e) {                    e.printStackTrace();                }            }        }.start();    } }

0 0