ImageLoaderWithCaches.java

package com.com.mr_wrong.ImageLoaderWithCaches;

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

import com.example.mr_wrong.androidstudioproject.R;

import java.io.BufferedInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.net.HttpURLConnection;
import java.net.URL;
import java.util.HashSet;
import java.util.Set;

/**
 * Created by Mr_Wrong on 2015/5/2.
 */
public class ImageLoaderWithCaches {
    private Set<ASyncDownloadImage> mTasks;
    private LruCache<String, Bitmap> mMemoryCaches;
    private ListView mListView;

    public ImageLoaderWithCaches(ListView listview) {
        this.mListView = listview;
        mTasks = new HashSet<ASyncDownloadImage>();
        int maxMemory = (int) Runtime.getRuntime().maxMemory();
        int cacheSize = maxMemory / 10;
        mMemoryCaches = new LruCache<String, Bitmap>(cacheSize) {
            @Override
            protected int sizeOf(String key, Bitmap value) {
                return value.getByteCount();
            }
        };
    }

    public void showImage(String url, ImageView imageView) {
        Bitmap bitmap = getBitmapFromMemoryCaches(url);
        if (bitmap == null) {
            imageView.setImageResource(R.mipmap.ic_launcher);
        } else {
            imageView.setImageBitmap(bitmap);
        }
    }

    public Bitmap getBitmapFromMemoryCaches(String url) {
        return mMemoryCaches.get(url);
    }

    public void addBitmapToMemoryCaches(String url, Bitmap bitmap) {
        if (getBitmapFromMemoryCaches(url) == null) {
            mMemoryCaches.put(url, bitmap);
        }
    }

    /**
     * 显示一个屏幕的图片
     * @param start
     * @param end
     */
    public void loadImages(int start, int end) {
        for (int i = start; i < end; i++) {
            String url = Images.IMAGE_URLS[i];
            Bitmap bitmap = getBitmapFromMemoryCaches(url);
            if (bitmap == null) {
                ASyncDownloadImage task = new ASyncDownloadImage(url);
                mTasks.add(task);
                task.execute(url);
            } else {
                ImageView imageView = (ImageView) mListView.findViewWithTag(url);
                imageView.setImageBitmap(bitmap);
            }
        }
    }

    /**
     * 下载图片
     * @param urlString
     * @return
     */
    private static Bitmap getBitmapFromUrl(String urlString) {
        Bitmap bitmap;
        InputStream is = null;
        try {
            URL url = new URL(urlString);
            HttpURLConnection conn = (HttpURLConnection) url.openConnection();
            is = new BufferedInputStream(conn.getInputStream());
            bitmap = BitmapFactory.decodeStream(is);
            conn.disconnect();
            return bitmap;
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            try {
                if (is != null)
                    is.close();
            } catch (IOException e) {
            }
        }
        return null;
    }

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

    class ASyncDownloadImage extends AsyncTask<String, Void, Bitmap> {

        private String url;

        public ASyncDownloadImage(String url) {
            this.url = url;
        }

        @Override
        protected Bitmap doInBackground(String... params) {
            url = params[0];
            Bitmap bitmap = getBitmapFromUrl(url);
            if (bitmap != null) {
                addBitmapToMemoryCaches(url, bitmap);
            }
            return bitmap;
        }

        @Override
        protected void onPostExecute(Bitmap bitmap) {
            super.onPostExecute(bitmap);
            ImageView imageView = (ImageView) mListView.findViewWithTag(url);
            if (imageView != null && bitmap != null) {
                imageView.setImageBitmap(bitmap);
            }
            mTasks.remove(this);
        }
    }
}