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[0]);
            
            InputStream is = null;
            ByteArrayOutputStream bos =new ByteArrayOutputStream();
            
            try {
                HttpResponse httpResponse = httpClient.execute(httpGet);//执行path
                if(httpResponse.getStatusLine().getStatusCode()==200){
                    is = httpResponse.getEntity().getContent();
                    
                    long total_length = httpResponse.getEntity().getContentLength();
                    int current_length = 0;
                    byte[] tmp = new byte[1024];
                    int len;
                    while((len=is.read(tmp))!=-1){
                        current_length+=len;
                        int update = (int)((float)current_length/total_length*100);
                        publishProgress(update);
                        bos.write(tmp, 0, len);
                    }
                    return bos.toByteArray();
                    
                }
            } catch (Exception e) {
                
            }finally{
                httpClient.getConnectionManager().shutdown();
            }
            
            return null;
        }
        
        @Override
        protected void onProgressUpdate(Integer... values) {
            dialog.setProgress(values[0]);
            super.onProgressUpdate(values);
        }
        
        @Override
        protected void onPostExecute(byte[] result) {
            if(result!=null){
                Bitmap bitmap = BitmapFactory.decodeByteArray(result, 0, 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"/>