Handler 和 AsyncTask的小实验

本文参照 http://blog.csdn.net/mylzc/article/details/6736988 和 http://blog.csdn.net/mylzc/article/details/6772129后

写了自己的代码， 和原作者的差不多， 条理很清晰。如果读下面的代码无障碍那么对handler和asynctask的使用自己应该也就会了。

上代码，这个最直白，哈哈：

package com.example.handlertest;

import org.apache.http.HttpResponse;
import org.apache.http.client.HttpClient;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.impl.client.DefaultHttpClient;

import android.annotation.SuppressLint;
import android.app.Activity;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.os.AsyncTask;
import android.os.Bundle;
import android.os.Handler;
import android.os.Message;
import android.view.Menu;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.ImageView;
import android.widget.ProgressBar;
import android.widget.TextView;
import android.widget.Toast;

public class MainActivity extends Activity implements OnClickListener{
    
    TextView tv1;
    TextView tv2;
    ImageView iv1;
    ImageView iv2;
    ProgressBar progressBar;
    
    private final static int OK = 0;
    private final static int BAD = 1;
    
    private MyHandler myHandler;
    private Thread thread;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        init();
        
    }

    private void init(){
        tv1 = (TextView)findViewById(R.id.getpicture);
        tv2 = (TextView)findViewById(R.id.getsecpicture);
        iv1 = (ImageView)findViewById(R.id.firstPic);
        iv2 = (ImageView)findViewById(R.id.secPic);
        progressBar = (ProgressBar)findViewById(R.id.progressBar);
        
        tv1.setOnClickListener(this);
        tv2.setOnClickListener(this);
        
        myHandler = new MyHandler();
        
    }
    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.activity_main, menu);
        return true;
    }

    @SuppressLint("HandlerLeak")
    @Override
    public void onClick(View arg0) {
        // TODO Auto-generated method stub
        if( arg0 == tv1){
            if(thread == null){
                thread = new Thread(runnable);
                thread.start();
            }else{
                 Toast.makeText(getApplication(), 
                         getApplication().getString(R.string.ThreadIsOn), Toast.LENGTH_LONG).show();  
            }
        }else if(arg0 == tv2){
            new MyAsyncTask().execute("http://csdnimg.cn/www/images/csdnindex_logo.gif");
        }
        else{
            ;
        }
    }
    
    @SuppressLint("HandlerLeak")
    class MyHandler extends Handler{
        public void handleMessage(Message msg){
            switch(msg.what){
            case OK:{
                Toast.makeText(getApplicationContext(), getString(R.string.ok), Toast.LENGTH_SHORT).show();
                iv1.setImageBitmap((Bitmap)msg.obj);
            }break;
            case BAD:{
                Toast.makeText(getApplicationContext(), getString(R.string.bad), Toast.LENGTH_SHORT).show();
            }break;
            default:{
                
            }break;
            }
        }
    }
    
    Runnable runnable = new Runnable() {
        public void run() {
            HttpClient hc = new DefaultHttpClient();
            HttpGet hg = new HttpGet("http://csdnimg.cn/www/images/csdnindex_logo.gif");
            Bitmap bm = null;
            try{
                HttpResponse hr = hc.execute(hg);
                bm = BitmapFactory.decodeStream(hr.getEntity().getContent());
            }catch(Exception  e){
                myHandler.obtainMessage(BAD).sendToTarget();
                return;
            }
            myHandler.obtainMessage(OK, bm).sendToTarget();
        }
    };
    
    class MyAsyncTask extends AsyncTask<String, Integer, Bitmap>{

        protected void onPreExecute () {
            iv2.setImageBitmap(null);
            progressBar.setProgress(0);
        }
        @Override
        protected Bitmap doInBackground(String... params) {
            // TODO Auto-generated method stub
            publishProgress(20); 
            HttpClient hc = new DefaultHttpClient();
            HttpGet hg = new HttpGet("http://csdnimg.cn/www/images/csdnindex_logo.gif");
            Bitmap bm = null;
            publishProgress(30);
            try {  
                HttpResponse hr = hc.execute(hg);  
                bm = BitmapFactory.decodeStream(hr.getEntity().getContent());  
            } catch (Exception e) {  
                return null;  
            }  
            publishProgress(100); 
            return bm;
        }
        
         protected void onProgressUpdate(Integer... progress) {
             progressBar.setProgress(progress[0]);
         }

         protected void onPostExecute(Bitmap result) {
             if(result != null) {  
                 Toast.makeText(getApplicationContext(), "成功获取图片", Toast.LENGTH_LONG).show();  
                 iv2.setImageBitmap(result);  
             }else {  
                 Toast.makeText(getApplicationContext(), "获取图片失败", Toast.LENGTH_LONG).show();  
             progressBar.setProgress(100);
         }

         }
    }

}

下面是我的xml主界面布局：

<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"
    tools:context=".MainActivity" >

    <TextView
        android:id="@+id/getpicture"
        android:clickable="true"
        android:layout_width="80dp"
        android:layout_height="80dp"
        android:text="@string/getPicture" />
    <ImageView 
        android:id="@+id/firstPic"
        android:contentDescription="csdnlogo"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_below="@id/getpicture"/>
    <TextView 
        android:id="@+id/getsecpicture"
        android:clickable="true"
        android:layout_width="80dp"
        android:layout_height="80dp"
        android:layout_below="@id/firstPic"
        android:text="@string/getPicture"
        />
    <ImageView 
        android:id="@+id/secPic"
        android:contentDescription="csdnlogo"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_below="@id/getsecpicture"/>
    
    <ProgressBar 
        android:layout_below="@id/secPic"
        android:id="@+id/progressBar"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content" 
        style="?android:attr/progressBarStyleHorizontal"/>

</RelativeLayout>

记得在manifest文件中加上联网权限声明：<uses-permission android:name="android.permission.INTERNET"></uses-permission>