1、上程式碼

activity_main.xml檔案

<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="com.example.handler.MainActivity" >

    <Button
        android:id="@+id/button1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="ParentToChile" />
    <Button
        android:layout_below="@+id/button1"
        android:id="@+id/button2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="ChileToParent" />
    <Button
        android:layout_below="@+id/button2"
        android:id="@+id/button3"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="ChileToChile" />

</RelativeLayout>
 

package com.example.handler;

import android.os.Bundle;
import android.os.Handler;
import android.os.Looper;
import android.os.Message;
import android.support.v7.app.ActionBarActivity;
import android.util.Log;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;

public class MainActivity extends ActionBarActivity {
	
	public static final String TAG = "HandlerTest";
	
	public Button mButtonPtoC;
	public Button mButtonCtoP;
	public Button mButtonCtoC;
	
	public Handler mHandlerCToP = new Handler(){
		@Override
		public void handleMessage(Message msg) {
			super.handleMessage(msg);
			switch(msg.what) {
				case 0:
					Log.d(TAG, "mHandlerCToP msg.what is 0");
					break;
				default:
					break;
			}
		}
	};
	public Handler mHandlerPToc = null;
	public Handler mHandlerCtoC = null;
	
	@Override
	protected void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		
		setContentView(R.layout.activity_main);
		mButtonPtoC = (Button)findViewById(R.id.button1);
		mButtonCtoP = (Button)findViewById(R.id.button2);
		mButtonCtoC = (Button)findViewById(R.id.button3);
		
		startChileThread("mHandlerPToc");
		startChileThread("mHandlerCtoC");
		
		mButtonPtoC.setOnClickListener(new OnClickListener(){
			@Override
			public void onClick(View v) {
				new Thread(new Runnable(){
					@Override
					public void run() {
						mHandlerCToP.sendEmptyMessage(0);
					}
				}).start();
			}
		});
		
		mButtonCtoP.setOnClickListener(new OnClickListener(){
			@Override
			public void onClick(View v) {
				mHandlerPToc.sendEmptyMessage(0);
			}
		});
		
		mButtonCtoC.setOnClickListener(new OnClickListener(){
			@Override
			public void onClick(View v) {
				new Thread(new Runnable(){
					@Override
					public void run() {
						mHandlerCtoC.sendEmptyMessage(0);
					}
				}).start();
			}
		});
	}
	
	//開啟一根執行緒
	public void startChileThread(final String type) {
		new Thread(new Runnable(){
			@Override
			public void run() {
				if (Looper.myLooper() == null) {
					Log.d(TAG, "Looper.myLooper() is  null");
					Looper.prepare();
				}
				else {
					Log.d(TAG, "Looper.myLooper() is not null");
				}
				if ("mHandlerPToc".equals(type)) {
					mHandlerPToc = new Handler() {
						@Override
						public void handleMessage(Message msg) {
							super.handleMessage(msg);
							switch(msg.what) {
								case 0:
									Log.d(TAG, "mHandlerPToc msg.what is 0");
									break;
								default:
									break;
							}
						}
					};
				} else if ("mHandlerCtoC".equals(type)) {
					mHandlerCtoC = new Handler() {
						@Override
						public void handleMessage(Message msg) {
							super.handleMessage(msg);
							switch(msg.what) {
								case 0:
									Log.d(TAG, "mHandlerCtoC msg.what is 0");
									break;
								default:
									break;
							}
						}
					};
				} 
				Looper.loop();
			}
		}).start();
	}
}
 

2、執行結果

控制檯列印

3、總結

後面還會講HandlerThread 實現子執行緒和子執行緒之間的通訊，然後還有講解Handler原始碼分析