AsyncTask实现下载图片

实现效果：

/*采用异步任务  AsyncTask<String,Integer, byte[]>
  * 参数一代表 执行异步任务时传递的参数的类型
  * 参数二 如果不采用进度，则填Void,否则填 Integer
  * 参数三 是指网络回传回来的数据类型
  */

客户端代码：

MainActivity.java

 package com.example.load_jpg;

 import java.io.ByteArrayOutputStream;
 import java.io.InputStream;

 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.app.Activity;
 import android.app.ProgressDialog;
 import android.content.Context;
 import android.graphics.Bitmap;
 import android.graphics.BitmapFactory;
 import android.os.AsyncTask;
 import android.os.Bundle;
 import android.view.View;
 import android.view.View.OnClickListener;
 import android.widget.Button;
 import android.widget.ImageView;
 import android.widget.Toast;

 public class MainActivity extends Activity {

     private ProgressDialog dialog;
     private ImageView iv;
     private Button btn;
     private final  static  String PATH="http://172.16.30.146:8080/Phone/a10.jpg";
     private Context context;

     @Override
     protected void onCreate(Bundle savedInstanceState) {
         super.onCreate(savedInstanceState);
         setContentView(R.layout.activity_main);
         context = this;
         init();
         btn.setOnClickListener(new OnClickListener() {
             @Override
             public void onClick(View v) {
                 new MyTask().execute(PATH);//执行异步任务
             }
         });
     }
     private void init() {
         iv  =(ImageView) findViewById(R.id.image);
         btn = (Button) findViewById(R.id.btn);
         dialog = new ProgressDialog(context);
         dialog.setCancelable(true);
         dialog.setTitle("提醒");
         dialog.setMessage("正在下载中...");
         dialog.setProgressStyle(ProgressDialog.STYLE_HORIZONTAL);
     }

     public class MyTask extends AsyncTask<String, Integer, byte[]>{

         @Override
         protected void onPreExecute() {//在异步符务执行之前 这个方法会被执行
             dialog.show();
             super.onPreExecute();
         }

         @Override
         protected byte[] doInBackground(String... params) {
             HttpClient httpClient = new DefaultHttpClient();
             HttpGet httpGet = new HttpGet(params[]);

             InputStream is = null;
             ByteArrayOutputStream bos =new ByteArrayOutputStream();

             try {
                 HttpResponse httpResponse = httpClient.execute(httpGet);//执行path
                 if(httpResponse.getStatusLine().getStatusCode()==){
                     is = httpResponse.getEntity().getContent();

                     long total_length = httpResponse.getEntity().getContentLength();
                     int current_length = ;
                     byte[] tmp = new byte[];
                     int len;
                     while((len=is.read(tmp))!=-){
                         current_length+=len;
                         int update = (int)((float)current_length/total_length*);
                         publishProgress(update);
                         bos.write(tmp, , len);
                     }
                     return bos.toByteArray();

                 }
             } catch (Exception e) {

             }finally{
                 httpClient.getConnectionManager().shutdown();
             }

             return null;
         }

         @Override
         protected void onProgressUpdate(Integer... values) {
             dialog.setProgress(values[]);
             super.onProgressUpdate(values);
         }

         @Override
         protected void onPostExecute(byte[] result) {
             if(result!=null){
                 Bitmap bitmap = BitmapFactory.decodeByteArray(result, , result.length);
                 iv.setImageBitmap(bitmap);
                 Toast.makeText(context, "下载成功", Toast.LENGTH_LONG).show();
             }else{
                 Toast.makeText(context, "下载失败", Toast.LENGTH_LONG).show();
             }
             dialog.dismiss();
             super.onPostExecute(result);
         }

     }

 }

activity_main.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"
     tools:context=".LoadPicActivity" >

     <ImageView
         android:id="@+id/image"
         android:layout_width="300dp"
         android:layout_height="300dp"
         android:src="@drawable/ic_launcher"
         />

  <Button
      android:id="@+id/btn"
        android:layout_width="match_parent"
         android:layout_height="wrap_content"
         android:text="下载"

      />
 </LinearLayout>

服务器端：建立web project，放入图片即可

最后在清单里注册：<uses-permission android:name="android.permission.INTERNET"/>