Android开发基础之Worker线程向Main线程发送消息

由于Worker线程不能修改UI，所以当在Worker线程中接收到消息之后，需要通知主线程来更新UI。

下面是一个下例子：

一 布局

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools" android:layout_width="match_parent"
    android:layout_height="match_parent" android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    android:paddingBottom="@dimen/activity_vertical_margin" tools:context=".MainActivity">

    <TextView android:text="default data."
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:id="@+id/textView" />

    <Button android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_below="@id/textView"
        android:text="download"
        android:id="@+id/button"/>

</RelativeLayout>

    private TextView textView;
    private Button button;
    private NetworkHandler handler_network;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        textView = (TextView)this.findViewById(R.id.textView);

        button = (Button)this.findViewById(R.id.button);
        button.setOnClickListener(new ButtonListener());

        handler_network = new NetworkHandler();
    }

    class ButtonListener implements View.OnClickListener {

        @Override
        public void onClick(View v) {
            NetworkThread thread = new NetworkThread();
            thread.start();
        }
    }

    class NetworkHandler extends Handler{
        public void handleMessage(Message msg){
            String str = (String)msg.obj;
            textView.setText(str);
        }
    }

    class NetworkThread extends Thread {
        public void run() {
            try {
                Thread.sleep(2 * 1000);
                String str = "data from net.";
                Message msg = handler_network.obtainMessage();
                msg.obj = str;
                handler_network.sendMessage(msg);
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    }