Android之Looper、Handler、Message、MessageQueue应用篇

简介

      上一篇文章介绍了Handler、Message、MessageQueue等Android线程交互方面的内容，Android之理解Looper、Handler、Message、MessageQueue。下面开始实践，学习如何去使用以及应用到程序里面。

实例

      在这里使用ListView作为异步下载图片的环境。

      1、Handle+Runnable

           实现思路是：

           1：在UI线程中启动一个线程,让这个线程去下载图片。

           2：图片完成下载后发送一个消息去通知UI线程

           3：UI线程获取到消息后，更新UI。

package com.example.handlerloadiage;

import java.io.IOException;
import java.net.URL;
import android.app.Activity;
import android.graphics.drawable.Drawable;
import android.os.Bundle;
import android.os.Handler;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.ImageView;
import android.widget.ListView;

public class Handler_Runnable_Mode extends Activity {

	private ListView listview;

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

		listview = (ListView) findViewById(R.id.listview);
		listview.setAdapter(new MyAdapter());
	}

	private class MyAdapter extends BaseAdapter {

		public MyAdapter() {

		}

		@Override
		public int getCount() {
			// TODO Auto-generated method stub
			return 100;
		}

		@Override
		public Object getItem(int position) {
			// TODO Auto-generated method stub
			return null;
		}

		@Override
		public long getItemId(int position) {
			// TODO Auto-generated method stub
			return 0;
		}

		@Override
		public View getView(int position, View convertView, ViewGroup parent) {
			if (convertView == null) {
				convertView = LayoutInflater.from(getApplicationContext())
						.inflate(R.layout.list_item, null);
			}
			final ImageView image = (ImageView) convertView
					.findViewById(R.id.imageview);
			final String imageURL = "http://avatar.csdn.net/D/1/4/3_wangjinyu501.jpg";

			Handler handler = new Handler();
			handler.post(new Runnable() {
				public void run() {
					Drawable drawable = null;
					try {
						drawable = Drawable.createFromStream(
								new URL(imageURL).openStream(), "image.jpg");
					} catch (IOException e) {
						Log.d("test", e.getMessage());
					}
					if (drawable == null) {
						Log.d("test", "null drawable");
					} else {
						Log.d("test", "not null drawable");
					}
					if (drawable == null) {
						image.setImageResource(R.drawable.ic_launcher);
					} else {
						image.setImageDrawable(drawable);
					}
				}
			});
			return convertView;
		}

	}

	@Override
	public boolean onCreateOptionsMenu(Menu menu) {
		getMenuInflater().inflate(R.menu.main, menu);
		return true;
	}

}

      效果如下：

                                                          

      快速滑动的过程中，还是出现了ANR的现象。

                                                           

     这是因为handler.post(new Runnable()这个方法，并没有开启一个新的线程，他还是在UI主线程中，所以导致出现ANR现象。

     2、Handle+Runnable+Message

    实现思路:

     实现代码：

package com.example.handlerloadiage;

import java.io.IOException;
import java.net.URL;
import android.app.Activity;
import android.graphics.drawable.Drawable;
import android.os.Bundle;
import android.os.Handler;
import android.os.Message;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.ImageView;
import android.widget.ListView;

public class Handler_Runnable_Mode extends Activity {

	private ListView listview;

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

		listview = (ListView) findViewById(R.id.listview);
		listview.setAdapter(new MyAdapter());
	}

	private class MyAdapter extends BaseAdapter {

		public MyAdapter() {

		}

		@Override
		public int getCount() {
			// TODO Auto-generated method stub
			return 100;
		}

		@Override
		public Object getItem(int position) {
			// TODO Auto-generated method stub
			return null;
		}

		@Override
		public long getItemId(int position) {
			// TODO Auto-generated method stub
			return 0;
		}

		@Override
		public View getView(int position, View convertView, ViewGroup parent) {
			if (convertView == null) {
				convertView = LayoutInflater.from(getApplicationContext())
						.inflate(R.layout.list_item, null);
			}
			final ImageView image = (ImageView) convertView
					.findViewById(R.id.imageview);
			final String imageURL = "http://avatar.csdn.net/D/1/4/3_wangjinyu501.jpg";

			final Handler handler = new Handler(){

				@Override
				public void handleMessage(Message msg) {
					
					super.handleMessage(msg);
					Drawable d=(Drawable) msg.obj;
					if (d == null) {
						image.setImageResource(R.drawable.ic_launcher);
					} else {
						image.setImageDrawable(d);
					}
				}
				
			};
			handler.post(new Runnable() {
				public void run() {
					Drawable drawable = null;
					try {
						drawable = Drawable.createFromStream(
								new URL(imageURL).openStream(), "image.jpg");
						Message message=handler.obtainMessage();
						message.obj=drawable;
						handler.sendMessage(message);
						
					} catch (IOException e) {
						Log.d("test", e.getMessage());
					}
					if (drawable == null) {
						Log.d("test", "null drawable");
					} else {
						Log.d("test", "not null drawable");
					}
					
				}
			});
			return convertView;
		}

	}

	@Override
	public boolean onCreateOptionsMenu(Menu menu) {
		getMenuInflater().inflate(R.menu.main, menu);
		return true;
	}

}

    也是会出现ANR的现象，原因和之前一样。