Android开发之Handler(3)

前面讲过如何从WorkThread向MainThread发送消息。也就是

（1）在主线程实现Handle的HandleMessage()方法；

（2）在WorkThread中通过Handle发送消息

这讲将要介绍如何从MainThread向WorkThread中发送消息，主要步骤：

（1）在workThread中准备looper对象

（2）生成Handler对象

（3）在MainThread中发送消息

//mainActivity
<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:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context=".MainActivity" >

    <TextView
        android:id="@+id/textViewId"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/hello_world" />
    <Button 
        android:id="@+id/buttonId"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text ="发送消息"/>
</RelativeLayout>

//MainActivity.java
package com.example.handlenew2;
import android.app.Activity;
import android.os.Bundle;
import android.os.Handler;
import android.os.Looper;
import android.os.Message;
import android.view.Menu;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;

public class MainActivity extends Activity {
private Button button;
private Handler handler;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
button = (Button)findViewById(R.id.buttonId);
button.setOnClickListener(new OnClickListener() {
public void onClick(View v) {
Message msg=handler.obtainMessage();
handler.sendMessage(msg);
}
});
WorkThread wt=new WorkThread();
wt.start();
}
class WorkThread extends Thread{
public void run(){
//准备looper对象
Looper.prepare();
//在WorkThread当中生成一个Handler对象
handler = new Handler(){
@Override
public void handleMessage(Message msg){
System.out.println("收到了消息对象");
}
 };
 //调用
 Looper.loop();
}
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.main, menu);
return true;
}

}