ImageLoader.java

package com.android.entity;

import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.os.AsyncTask;
import android.os.Handler;
import android.os.Message;
import android.util.LruCache;
import android.widget.ImageView;
import android.widget.ListView;

import com.android.adapter.NewsAdapter;
import com.android.play.R;

import java.awt.font.TextAttribute;
import java.io.BufferedInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.StringReader;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.URL;
import java.util.HashSet;
import java.util.Set;

/**
 * Created by Administrator on 2016/6/7.
 */
public class ImageLoader {
    private ImageView mImageView;
    private String mUrl;
    //创建Cache 缓存
    private LruCache<String, Bitmap> mCaches;
    private ListView mListView;
    private Set<NewsAsyncTask> mTask;

    public ImageLoader(ListView listView){
        mListView = listView;
        mTask = new HashSet<>();

        //获取最大可用内存
        int maxMemory = (int) Runtime.getRuntime().maxMemory();
        int cacheSize = maxMemory/4;
        /*匿名内部类*/
        mCaches = new LruCache<String, Bitmap>(cacheSize){
            @Override
            protected int sizeOf(String key, Bitmap value) {
                //在每次存入缓存的时候调用
                return value.getByteCount();
            }
        };
    }
    //增加到缓存，增加的同时判断是否已经存在
    public void addBitmapToCache(String url, Bitmap bitmap){
        if (getBitmapFromCache(url) == null){
            mCaches.put(url,bitmap);
        }
    }

    //从缓存中获取数据
    public Bitmap getBitmapFromCache(String url){
        return mCaches.get(url);
    }

    private Handler handler = new Handler(){
        @Override
        public void handleMessage(Message msg) {
            super.handleMessage(msg);
            if (mImageView.getTag().equals(mUrl)) {
                mImageView.setImageBitmap((Bitmap) msg.obj);
            }
        }
    };


    public void showImageByThread(ImageView imageView, final String url){
        mImageView = imageView;
        mUrl = url;
        new Thread(){
            @Override
            public void run() {
                super.run();

                Bitmap bitmap = getBitmapFromURL(url);
                Message message = Message.obtain(); //使用现有的 回收掉的Message，提高效率
                message.obj = bitmap;
                handler.sendMessage(message);

            }
        }.start();

    }

    //  通过一个网络上的url来转换成图片
    public Bitmap getBitmapFromURL(String urlString){
        Bitmap bitmap;
        InputStream is = null;

        try {
            URL url = new URL(urlString);
            HttpURLConnection connection = (HttpURLConnection) url.openConnection();
            is = new BufferedInputStream(connection.getInputStream());
            bitmap = BitmapFactory.decodeStream(is);
            connection.disconnect();
            return bitmap;

        } catch (MalformedURLException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }finally {
            try {
                is.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
        return null;
    }
//通过AsyncTask加载图片
    public void showImageByAsyncTask(ImageView imageView, String url){
        //从缓存中取出对应图片，如果缓存没有，必须去下载
        Bitmap bitmap = getBitmapFromCache(url);
        if(bitmap == null) {
            imageView.setImageResource(R.mipmap.ic_launcher);
        }else {
            imageView.setImageBitmap(bitmap);
        }
    }

    private class NewsAsyncTask extends AsyncTask<String, Void, Bitmap>{
      //  private ImageView mImageView;
        private String mUrl;

        public NewsAsyncTask(/*ImageView imageView,*/ String url){
          //  mImageView = imageView;
            mUrl = url;
        }

        @Override
        protected Bitmap doInBackground(String... params) {
            //从网络获取图片，下载完毕后将不在缓存中的图片加入缓存
            String url = params[0];
            Bitmap bitmap = getBitmapFromURL(url);
            if (bitmap != null){
                addBitmapToCache(url, bitmap);
            }
            return bitmap;
        }

        @Override
        protected void onPostExecute(Bitmap bitmap) {
            super.onPostExecute(bitmap);
           /* if(mImageView.getTag().equals(mUrl)) {
                mImageView.setImageBitmap(bitmap);
            }*/
            ImageView imageView = (ImageView) mListView.findViewWithTag(mUrl);
            if (imageView != null && bitmap != null){
                imageView.setImageBitmap(bitmap);
            }
            mTask.remove(this);
        }
    }

    //用来加载从start 到end的所有图片
    public void loadImages(int start, int end){
        for (int i = start; i<end;i++){
            String url = NewsAdapter.URLS[i];
            Bitmap bitmap = getBitmapFromCache(url);
            if (bitmap == null){
                NewsAsyncTask task = new NewsAsyncTask(url);
                task.execute(url);
                mTask.add(task);
            }else {
                ImageView imageView = (ImageView) mListView.findViewWithTag(url);
                imageView.setImageBitmap(bitmap);
            }
        }
    }

    public void cancelAllTasks(){
        if(mTask != null){
            for (NewsAsyncTask task : mTask){
                task.cancel(false);
            }
        }
    }
}