Monday, July 30, 2012

Apply LruCache on GridView

The example "Caching Bitmaps with LruCache" provide a example to Apply LruCache on Gallery. This exercise is GridView version using LruCache.


GridView with LruCache

To using android.util.LruCache in the code, targetSdkVersion of "13" is needed to be specified in AndroidManifest.xml.

The layout file, refer to the post "GridView loading photos from SD Card".

package com.example.androidgridview;

import java.lang.ref.WeakReference;
import java.util.ArrayList;

import android.os.AsyncTask;
import android.os.Bundle;
import android.os.Environment;
import android.content.Context;
import android.util.LruCache;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.GridView;
import android.widget.ImageView;
import android.widget.Toast;

public class MainActivity extends Activity {

    public class ImageAdapter extends BaseAdapter {
     private Context mContext;
     ArrayList<String> itemList = new ArrayList<String>();
     public ImageAdapter(Context c) {
      mContext = c; 
     void add(String path){

  public int getCount() {
   return itemList.size();

  public Object getItem(int arg0) {
   // TODO Auto-generated method stub
   return null;

  public long getItemId(int position) {
   // TODO Auto-generated method stub
   return 0;

  public View getView(int position, View convertView, ViewGroup parent) {
   ImageView imageView;
         if (convertView == null) {  // if it's not recycled, initialize some attributes
             imageView = new ImageView(mContext);
             imageView.setLayoutParams(new GridView.LayoutParams(220, 220));
             imageView.setPadding(8, 8, 8, 8);
         } else {
             imageView = (ImageView) convertView;

         //Bitmap bm = decodeSampledBitmapFromUri(itemList.get(position), 220, 220);
         // Use the path as the key to LruCache
         final String imageKey = itemList.get(position);
           final Bitmap bm = getBitmapFromMemCache(imageKey);
         if (bm == null){
          BitmapWorkerTask task = new BitmapWorkerTask(imageView);

         return imageView;
  public Bitmap decodeSampledBitmapFromUri(String path, int reqWidth, int reqHeight) {
   Bitmap bm = null;
   // First decode with inJustDecodeBounds=true to check dimensions
   final BitmapFactory.Options options = new BitmapFactory.Options();
   options.inJustDecodeBounds = true;
   BitmapFactory.decodeFile(path, options);
   // Calculate inSampleSize
   options.inSampleSize = calculateInSampleSize(options, reqWidth, reqHeight);
   // Decode bitmap with inSampleSize set
   options.inJustDecodeBounds = false;
   bm = BitmapFactory.decodeFile(path, options); 
   return bm;   
  public int calculateInSampleSize(
   BitmapFactory.Options options, int reqWidth, int reqHeight) {
   // Raw height and width of image
   final int height = options.outHeight;
   final int width = options.outWidth;
   int inSampleSize = 1;
   if (height > reqHeight || width > reqWidth) {
    if (width > height) {
     inSampleSize = Math.round((float)height / (float)reqHeight);    
    } else {
     inSampleSize = Math.round((float)width / (float)reqWidth);    
   return inSampleSize;    
  class BitmapWorkerTask extends AsyncTask<String, Void, Bitmap>{
   private final WeakReference<ImageView> imageViewReference;
   public BitmapWorkerTask(ImageView imageView) {
    // Use a WeakReference to ensure the ImageView can be garbage collected
    imageViewReference = new WeakReference<ImageView>(imageView); 
   protected Bitmap doInBackground(String... params) {
    final Bitmap bitmap = decodeSampledBitmapFromUri(params[0], 200, 200);
    addBitmapToMemoryCache(String.valueOf(params[0]), bitmap);
    return bitmap;

   protected void onPostExecute(Bitmap bitmap) {
    if (imageViewReference != null && bitmap != null) {
     final ImageView imageView = (ImageView)imageViewReference.get();
     if (imageView != null) {

    ImageAdapter myImageAdapter;
    private LruCache<String, Bitmap> mMemoryCache;

    public void onCreate(Bundle savedInstanceState) {
        GridView gridview = (GridView) findViewById(;
        myImageAdapter = new ImageAdapter(this);
        String ExternalStorageDirectoryPath = Environment
        String targetPath = ExternalStorageDirectoryPath + "/test/";
        Toast.makeText(getApplicationContext(), targetPath, Toast.LENGTH_LONG).show();
        File targetDirector = new File(targetPath);
        File[] files = targetDirector.listFiles();
        for (File file : files){
        // Get memory class of this device, exceeding this amount will throw an
        // OutOfMemory exception.
        final int memClass 
         = ((ActivityManager)getSystemService(Context.ACTIVITY_SERVICE))
        // Use 1/8th of the available memory for this memory cache.
        final int cacheSize = 1024 * 1024 * memClass / 8;
        mMemoryCache = new LruCache<String, Bitmap>(cacheSize) {
         protected int sizeOf(String key, Bitmap bitmap) {
          // The cache size will be measured in bytes rather than number of items.
          return bitmap.getByteCount(); 
 public void addBitmapToMemoryCache(String key, Bitmap bitmap) {
  if (getBitmapFromMemCache(key) == null) {
   mMemoryCache.put(key, bitmap); 
 public Bitmap getBitmapFromMemCache(String key) {
  return (Bitmap) mMemoryCache.get(key); 


Download the files.


kikko088 said...

I have a problem whit this example, whit a lot of image the cell don't have the correct image, I think that the when the task is complete it change the image also if the cell is not the starting can I correct this little problem?

kikko088 said...

Hi very great tutorial but I have a question, I try to implement this into my application, the grid is so smooth but some time the image are overlapping, I think that the problem is that the asynctask on postexecute set the image also if we are on the wrong cell, how can I remove this problem?I try to load more or less 50images, the total dimension are more or less 60mb.
thank you very much

Andr.oid Eric said...

Hello kikko088,

Do you have the same problem without LruCache? GridView loading photos from SD Card. - to identify the problem come from GridView or LruCache.