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。