Android Open Source - ImageScanner Image Loader Cache Helper

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License

The source code is released under:

Apache License

Java Source Code

package com.scanner.utils;
//w  ww  .  j  a va2  s.c  o  m
import java.util.HashSet;
import java.util.Set;

import android.content.Context;
import android.graphics.Bitmap;
import android.os.AsyncTask;
import android.util.LruCache;
import android.view.View;
import android.widget.ImageView;

/**
 * ImageLoaderCacheHelper 
 * 
 * @author Quinn
 * 
 */
public class ImageLoaderCacheHelper {

  public interface SetImageCallBack {
    public void setImage(ImageView imageView, Bitmap bitmap);
  }

  private final static String TAG = "ImageLoaderCacheHelper";

  
  private LruCache<String, Bitmap> mMemoryCache;
  private Set<BitmapWorkerTask> taskCollection;


  private static Context context;

  private static ImageLoaderCacheHelper instance = null;

  public static ImageLoaderCacheHelper getInstance(Context context) {
    synchronized (ImageLoaderCacheHelper.class) {
      if (instance == null) {
        instance = new ImageLoaderCacheHelper(context);
        ImageLoaderCacheHelper.context = context;
      }
    }
    return instance;
  }

  private ImageLoaderCacheHelper(Context context) {

    taskCollection = new HashSet<BitmapWorkerTask>();
    int maxMemory = (int) Runtime.getRuntime().maxMemory();
    int cacheSize = maxMemory / 8;
    mMemoryCache = new LruCache<String, Bitmap>(cacheSize) {
      @Override
      protected int sizeOf(String key, Bitmap bitmap) {
        return bitmap.getByteCount();
      }
    };

  }

  
  public void addBitmapToMemoryCache(String key, Bitmap bitmap) {
    if (getBitmapFromMemoryCache(key) == null) {
      mMemoryCache.put(key, bitmap);
    }
  }


  public Bitmap getBitmapFromMemoryCache(String key) {
    return mMemoryCache.get(key);
  }


  
  public void loadBitmaps(ImageView imageView, String imageUrl,
      View defaultView, SetImageCallBack callback) {

    try {
      Bitmap bitmap = getBitmapFromMemoryCache(imageUrl);
      if (bitmap == null) {
        /**
         * if bitmap is null, load it with a task;
         */
        BitmapWorkerTask task = new BitmapWorkerTask(imageView,
            defaultView, callback);
        taskCollection.add(task);
        task.execute(imageUrl);

      } else {
        if (imageView != null && bitmap != null) {
          callback.setImage(imageView, bitmap);
          crossfade(defaultView, imageView);
        }
      }
    } catch (Exception e) {
      e.printStackTrace();
    }
  }

  /**
   * The task to load a image
   * 
   * @author Quinn
   */
  class BitmapWorkerTask extends AsyncTask<String, Void, Bitmap> {

    
    private ImageView imageView;
    private String imageUrl;
    private SetImageCallBack callback;
    private View defaultView;

    public BitmapWorkerTask(ImageView imageView, View defaultView,
        SetImageCallBack callback) {
      this.imageView = imageView;
      this.callback = callback;
      this.defaultView = defaultView;
    }

    @Override
    protected Bitmap doInBackground(String... params) {
      imageUrl = params[0];
      Bitmap bitmap = loadBitmap(imageUrl);
      addBitmapToMemoryCache(imageUrl, bitmap);
      return bitmap;
    }

    @Override
    protected void onPostExecute(Bitmap bitmap) {
      super.onPostExecute(bitmap);

      if (imageView != null && bitmap != null) {
        callback.setImage(imageView, bitmap);
        crossfade(defaultView, imageView);
      }
      taskCollection.remove(this);
    }

    private Bitmap loadBitmap(String imageUrl) {

      int rectSize = DensityUtil.getScreenHeight(context) / 16;
      Bitmap bitmap0 = BitmapUtils.decodeBitmapFromFile(imageUrl,
          rectSize , rectSize);
      Bitmap bitmap1 = BitmapUtils.centerSquareScaleBitmap(bitmap0,
          rectSize);
      return bitmap1;
    }

  }

  private void crossfade(final View currView, View nextView) {

    if (nextView != null) {

      nextView.setVisibility(View.VISIBLE);

    }

    if (currView != null) {

      currView.setVisibility(View.GONE);

    }
  }

}

Java Source Code List

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