Android中使用ImageView控件显示网络图片

在android4.0以后的版本中,为了使得主界面流畅,所以设置了不允许在主线程中访问网络,为了安全,又不允许在其它线程中访问控件,这样就造成了ImageView等需要使用网络的控件更新时的问题,本文以Handler+Runnable的方式实现了ImageView控件显示网络图片.

在android4.0之后,如果在主线程中访问网络,会报一个android.os.networkonmainthreadexception的异常.因为在ui线程中访问网络的话,就要等待网络传输完成,期间就会阻塞线程,使界面卡住.

为了访问网络资源,可以开启一个线程,异步加载.但这个新线程又不具有更新控件的能力,所以就需要一个中间人来完成ui线程和网络线程的联系,本文使用的是消息机制,网络线程发送一个消息,ui线程中收到后执行相应工作.

package com.example.netimage;

 

import java.io.InputStream;

import java.net.HttpURLConnection;

import java.net.URL;

 

import android.os.Bundle;

import android.os.Handler;

import android.os.Message;

import android.app.Activity;

import android.graphics.Bitmap;

import android.graphics.BitmapFactory;

import android.view.Menu;

import android.view.View;

import android.widget.Button;

import android.widget.EditText;

import android.widget.ImageView;

 

public class MainActivity extends Activity {

     

     private Button b;

     private EditText et;

     public ImageView iv;

 

     @Override

     protected void onCreate(Bundle savedInstanceState) {

         super .onCreate(savedInstanceState);

         setContentView(R.layout.activity_main);

         

         b = (Button) this .findViewById(R.id.button1);

         b.setOnClickListener( new ButtonOnClickListener());

         

         iv = (ImageView) this .findViewById(R.id.imageView1);

         et = (EditText) this .findViewById(R.id.editText1);

     }

     

     private Handler handler = new Handler() { 

         public void handleMessage (Message msg) { // 此方法在ui线程运行 

             switch (msg.what) { 

             case 1 : 

                 iv.setImageBitmap((Bitmap) msg.obj); // iv 显示从网络获取到的logo   

                 break ;  

             } 

         } 

     };

     

     class download implements Runnable{

         

         @Override

         public void run() {

             // TODO Auto-generated method stub

             String path = et.getText().toString();

             try {

                 

                 //byte[] data = ImageService.getImage(path);

                 URL url = new URL(path);

                 HttpURLConnection con = (HttpURLConnection)url.openConnection();

                 con.setConnectTimeout( 5000 );

                 con.setRequestMethod( "GET" );

                 con.connect();

                 

                 if (con.getResponseCode() == 200 ){         

                     InputStream is = con.getInputStream();

                     //byte[] data = StreamTool.readStream(is);

                     Bitmap bitmap = BitmapFactory.decodeStream(is); //(data, 0, data.length);

                     handler.obtainMessage( 1 ,bitmap).sendToTarget();

                 }

                 //Bitmap bitmap = BitmapFactory.decodeByteArray(data, 0, data.length);

                 //ImageView iv = (ImageView)con.findViewById(R.id.imageView1);

             } catch (Exception e) {

                 // TODO Auto-generated catch block

                 e.printStackTrace();

             }

             

         }

     }

     

     private class ButtonOnClickListener implements View.OnClickListener{

 

         @Override

         public void onClick(View v) {

             // TODO Auto-generated method stub

             new Thread( new download()).start();

         }

         

     }

 

     @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 ;

     }

 

}