Android中的Handler机制

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：

查看源码

01public class HandlerTestActivity extendsActivity {

02    privateTextView tv;

03    privatestatic final int UPDATE = 0;

04    privateHandler handler = newHandler() {

05 

06        @Override

07        publicvoid handleMessage(Message msg) {

08            // TODO 接收消息并且去更新UI线程上的控件内容

09            if(msg.what == UPDATE) {

10                // Bundle b = msg.getData();

11                // tv.setText(b.getString("num"));

12                tv.setText(String.valueOf(msg.obj));

13            }

14            super.handleMessage(msg);

15        }

16    };

17 

18    /** Called when the activity is first created. */

19    @Override

20    publicvoid onCreate(Bundle savedInstanceState) {

21        super.onCreate(savedInstanceState);

22        setContentView(R.layout.main);

23        tv = (TextView) findViewById(R.id.tv);

24 

25        newThread() {

26            @Override

27            publicvoid run() {

28                // TODO 子线程中通过handler发送消息给handler接收，由handler去更新TextView的值

29                try{

30                    for(int i = 0; i < 100; i++) {

31                        Thread.sleep(500);

32                        Message msg =new Message();

33                        msg.what = UPDATE;

34                        // Bundle b = new Bundle();

35                        // b.putString("num", "更新后的值：" + i);

36                        // msg.setData(b);

37                        msg.obj ="更新后的值：" + i;

38                        handler.sendMessage(msg);

39                    }

40                }catch (InterruptedException e) {

41                    e.printStackTrace();

42                }

43            }

44        }.start();

45    }

46 

47}

        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。