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I am trying follow this answer to cache the bitmaps that I need to display in a listview. But there is no mentioning anywhere on how to use it in a class. Can anyone give me a sample code on how to use the DiskLruImageCache in a class?

EDIT

This is what I tried. I have many activities, so I am using a singleton class named Model. I created instance of DiskLruImageCache inside model class and on the onCreate of the first activity I initialise the object like this: 

private DiskLruImageCache diskLruImageCache;

public void prepareCache(Context context) {
    diskLruImageCache = new DiskLruImageCache(context, "myappcache", 10, CompressFormat.JPEG, 100);
}

Then I have these two methods in the Model class to store and get the bitmaps:

public void storeBitmapToCache(String key, Bitmap bitmap) {
    diskLruImageCache.put(key, bitmap);
}

public Bitmap getBitmapFromCache(String key) {
    return diskLruImageCache. getBitmap(key);
}

Then in a class I need to store an image, I do:

Model.getInstance().storeBitmapToCache("mykey",bitmap); //Model.getInstance() gets the current instance of the singletonclass

And to get it I use:

Model.getInstance().getBitmapFromCache("mykey");

But I was not getting the bitmap. Then I tried debugging and figured out that the image is getting stored in the cache, since the following is getting executed in DiskLruImageCache.java when I try to save the bitmap.

if( writeBitmapToFile( data, editor ) ) {               
    mDiskCache.flush();
    editor.commit();
    if ( BuildConfig.DEBUG ) {
        Log.d( "cache_test_DISK_", "image put on disk cache " + key ); //this line is getting printed
    }
}

Which means the image is cached. But when I tried to get the bitmap, the following is getting executed in DiskLruImageCache.java

snapshot = mDiskCache.get( key );
if ( snapshot == null ) {
    return null; //it is null and so is returning here
}
//hence the following which actually gets the bitmap fro cache is never getting executed.
final InputStream in = snapshot.getInputStream( 0 );
if ( in != null ) {
    final BufferedInputStream buffIn = 
    new BufferedInputStream( in, Utils.IO_BUFFER_SIZE );
    bitmap = BitmapFactory.decodeStream( buffIn );              
}

And then I checked to see if the key "mykey" which I used to store the bitmap is there in the cache by using the containsKey(String key) method in DiskLruImageCache.java, but it also returns a false. That is even the key I used to store the bitmap is not there and it IS getting stored. Is it any problem with what I am doing? Because I found out that lots of people are getting it working correctly from the answer. What am I doing wrong here? How to rectify this?

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  • did you check that `Model.getInstance()` returns the same instance? – 18446744073709551615 Aug 12 '14 at 06:19
  • Yes.. It is not just for this purpose I use model. I already had a model class in which I just added this methods. It is a singleton. There is only one instance of the class throughout the app. So there is no question of `same instance`. – Harikrishnan Aug 12 '14 at 06:25
  • Just in case, add logging to the code that creates the singleton. It is theoretically possible that the process gets killed and restarted. (Anyway, you likely have already found the problem; please post your own answer in this case.) – 18446744073709551615 Aug 12 '14 at 12:59
  • As I already said, I am using the same singleton for a lots of other purposes as well, and caching is just one of them. All other are working perfectly well, so obviously it is not a problem with model. And without any documentation found, I am still struggling to find the solution. :( – Harikrishnan Aug 12 '14 at 13:27
  • It may sound as opposite to what we are told to believe, but for small projects it is sometimes easier to write your own code than to debug someone else's one. The pessimistic estimate for a disk cache is 2 work days, while debugging may take a week and nobody knows if it will be successful. A 3rd option is to write unit tests for the code that you want to borrow... if you can find where to start. – 18446744073709551615 Aug 13 '14 at 15:29
  • It is not a small project and I am not sure if it is a problem with the code since so many people have got it working. It should be something that I do. – Harikrishnan Aug 14 '14 at 05:07

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