异步任务下载网络图片

package com.example.mydouban;

import java.io.IOException;
import java.io.InputStream;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.URL;

import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.os.AsyncTask;

public class LoadImageAsynTask extends AsyncTask<String, Void, Bitmap>{

    LoadImageAsynTaskCallBack loadImageAsynTaskCallBack;

    public LoadImageAsynTask(LoadImageAsynTaskCallBack loadImageAsynTaskCallBack){

        this.loadImageAsynTaskCallBack=loadImageAsynTaskCallBack;

    }

    //设置回调接口
    public interface LoadImageAsynTaskCallBack{

        public void beforeLoadImage();
        public void afterLoadImage();
    }


    /*
     * 异步任务执行之前调用
     */
    @Override
    protected void onPreExecute() {
        //具体执行什么操作LoadImageAsynTask不知道
        //让调用LoadImageAsynTask的人去实现
        loadImageAsynTaskCallBack.beforeLoadImage();

        super.onPreExecute();
    }

    /*
     * 异步任务执行之后调用
     */

    @Override
    protected void onPostExecute(Bitmap result) {
        // TODO Auto-generated method stub
        loadImageAsynTaskCallBack.afterLoadImage();
        super.onPostExecute(result);
    }

    /*
     * 后台子线程运行的异步任务
     */

    @Override
    protected Bitmap doInBackground(String... params) {


        try {
            String path=params[0];
            URL url=new URL(path);
            HttpURLConnection conn=(HttpURLConnection) url.openConnection();
            InputStream is=conn.getInputStream();
            return BitmapFactory.decodeStream(is);

        } catch (MalformedURLException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
            return null;
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
            return null;
        }


    }


//  调用这个异步任务并且sd卡缓存图片
//加入两个sd卡的权限  WRITE_EXTERNAL_STORAGE  MOUNT_NUMOUNT_FILESYSTEM

    //获取图片的名称
    String iconurl=url;
    String iconName=iconurl.substring(iconurl.lastIndexOf("/")+1, iconurl.length());

    File file=new File("/sdcard/"+iconName);
    if(file.exists()){
        iv_icon.setImageURI(Uri.fromFile(file));
    }else{

    LoadImageAsynTask task=new LoadImageAsynTask(new LoadImageAsynTaskCallBack() {

        @Override
        public void beforeLoadImage() {
            // TODO Auto-generated method stub
            iv_icon.setImageResource();

        }

        @Override
        public void afterLoadImage(Bitmap bitmap) {
            // TODO Auto-generated method stub
            if(bitmap!=null){
                iv_icon.setImageBitmap(bitmap);
                //把图片保存到sd卡上
                File file=new File("/sdcard/"+iconName);
                FileOutputStream stream=new FileOutputStream(file);
                bitmap.compress(CompressFormat.JPEG, 100, stream);
            }
            else{
                iv_icon.setImageResource();
            }
        }
    });
    task.execute(url);

    }
}