Handler使用方法总结

在看这篇博客之前，最好看看《Anroid异步消息机制（Handler、Looper、Message、MessageQueue）以及ThreadLocal运用》了解Handler原理。

Handler使用，主要有以下几种方式：

Thread+Handler、Timer+TimerTask+Handler、Handler.postXXX(Runnable r,...)、Handler.sendXXX()、AsyncTask。

1、activity_handler.xml

<LinearLayout 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:orientation="vertical"
    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/handler_post_text"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="handler.post()" />

    <TextView
        android:id="@+id/timer_handler_text"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Timer+TimerTask+Handler" />
    
    <TextView
        android:id="@+id/thread_handler_text"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="thread+handler" /> 
      
    <TextView
        android:id="@+id/asyncTask_text"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="asyncTask" /> 
    
    <Button
        android:id="@+id/thread_handler_button"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="thread+handler" /> 
        
    <Button
        android:id="@+id/asyncTask_button"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="asyncTask" />

</LinearLayout>

2、HandlerExample.java

import java.lang.ref.WeakReference;
import java.util.Timer;
import java.util.TimerTask;

import android.app.Activity;
import android.os.AsyncTask;
import android.os.Bundle;
import android.os.Handler;
import android.os.Message;
import android.os.SystemClock;
import android.view.Menu;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.TextView;

public class HandlerExample extends Activity {

	private TextView handler_post_text = null;

	private TextView timer_handler_text = null;

	private TextView thread_handler_text = null;
	
	private TextView asyncTask_text = null;

	private Button thread_handler_button = null;
	
	private Button asyncTask_button =null;

	private Handler handler;

	private Timer timer;
	
	private AsyncTask asyncTask;

	@Override
	protected void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.activity_handler);
		//WeakReference<Handler> wf = new WeakReference<Handler>(new MyHandler());
		//handler = (wf != null) ? wf.get() : null;
		handler = new MyHandler();
		timer = new Timer();
		timer.schedule(new MyTimer(), 1, 5000);
		handler_post_text = (TextView) findViewById(R.id.handler_post_text);
		timer_handler_text = (TextView) findViewById(R.id.timer_handler_text);
		thread_handler_text = (TextView) findViewById(R.id.thread_handler_text);
		asyncTask_text = (TextView) findViewById(R.id.asyncTask_text);
		thread_handler_button = (Button) findViewById(R.id.thread_handler_button);
		asyncTask_button = (Button) findViewById(R.id.asyncTask_button);
		thread_handler_button.setOnClickListener(new OnClickListener() {

			@Override
			public void onClick(View arg0) {
				new Thread(new Runnable() {

					@Override
					public void run() {
						Message message = new Message();
						message.what = 2;
						handler.sendMessage(message);
						// handler.sendEmptyMessage(int what);
						// handler.sendEmptyMessageAtTime(int what, long uptimeMillis);//什么时间执行发送消息
						// handler.sendEmptyMessageDelayed(int what, long delayMillis);//延迟多少执行发送消息
						// handler.sendMessageAtTime(Message msg, long uptimeMillis);//什么时间执行发送消息
						// handler.sendMessageDelayed(Message msg, long uptimeMillis);//延迟多少执行发送消息
					}
				}).start();
			}

		});
		asyncTask_button.setOnClickListener(new OnClickListener() {
			@Override
			public void onClick(View arg0) {
				asyncTask = new MyAsyncTask();//需要在UI线程中进行
				asyncTask.execute("hello world");//需要在UI线程中进行
				//asyncTask.execute(Runnable runnable);
				//asyncTask.execute(Object o);
				//asyncTask.execute(Object... params);
			}
		});
		handler.postAtTime(new Runnable() {
			@Override
			public void run() {
				handler_post_text.setText("MainActivity.handler_post."
						+ Thread.currentThread().getName() + "-"
						+ Thread.currentThread().getId());
			}
		}, handler_post_text, SystemClock.uptimeMillis() + 4000);// 默认Message
		// handler.post(Runnable r);
		// handler.postAtTime(Runnable r, long uptimeMillis);//什么时间执行发送消息
		// handler.postDelayed(Runnable r, long uptimeMillis);//延迟多少执行发送消息
	}

	@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;
	}

	// 设置定时器任务
	class MyTimer extends TimerTask {
		@Override
		public void run() {
			Message message = new Message();
			message.what = 1;
			handler.sendMessage(message);
		}
	}
	//onPreExecute->doInBackground->onProgressUpdate(需要doInBackground调用了publishProgress才能通过Handler触发)->onPostExecute(可无)
	//第一个参数是execute方法、doInBackground方法参数类型；
	//第二个参数是onProgressUpdate方法的参数类型；
	//第三个参数是onPostExecute方法的参数类型以及doInBackground返回参数类型
	class MyAsyncTask extends AsyncTask<Object, Integer, String>{

		@Override
		protected void onPreExecute(){//可以ui更新
			asyncTask_text.setText("MainActivity.asyncTask."
					+ Thread.currentThread().getName() + "-"
					+ Thread.currentThread().getId());
		}
		@Override
		protected String doInBackground(Object... arg0) {//可以执行耗时的任务，因而不能执行ui更新
			return "AsyncTask";
		}
		@Override
		protected void onProgressUpdate(Integer... progresses){
			
		}
		@Override
		protected void onPostExecute(String result){//更新ui，显示结果
			asyncTask_text.setText("AsyncTask");
		}
		@Override
		protected void onCancelled(){//取消执行任务时，更新ui
			
		}
	}

	final class MyHandler extends Handler {
		@Override
		public void handleMessage(Message message) {
			if (message.what == 1) {
				timer_handler_text.setText("MainActivity.timer_handler."
						+ Thread.currentThread().getName() + "-"
						+ Thread.currentThread().getId());
			} else if (message.what == 2) {
				thread_handler_text.setText("MainActivity.thread_handler."
						+ Thread.currentThread().getName() + "-"
						+ Thread.currentThread().getId());
			}
		}
	}

	@Override
	protected void onStop() {
		super.onStop();
	}

	@Override
	protected void onDestroy() {
		super.onDestroy();
		if (timer != null) {
			timer.cancel();
		}
		if (handler != null) {
			handler.removeCallbacksAndMessages(null);// 释放Handler
		}
	}

	@Override
	protected void onResume() {
		super.onResume();
	}
}

3、AsyncTask

对Thread+Handler进行包装，更加流程化来处理UI。概括来说，当我们在UI线程中调用execute()方法后会调用onPreExecute()方法，然后由ThreadPoolExecutor实例sExecutor执行一个FutureTask任务，这个过程中doInBackground()方法将被调用，如果被开发者覆写的doInBackground()方法中调用了publishProgress()方法，则通过InternalHandler实例sHandler发送一条MESSAGE_POST_PROGRESS消息，更新进度；sHandler处理消息时onProgressUpdate()方法将被调用；如果遇到异常，则发送一条MESSAGE_POST_CANCEL的消息，取消任务，sHandler处理消息时onCancelled()方法将被调用；如果执行成功，则发送一条MESSAGE_POST_RESULT的消息，显示结果，sHandler处理消息时onPostExecute(Result result)方法被调用。

如下图所示：