Useful Info

1. Caching is NOT enabled by default. If you want loaded images to be cached in memory and/or on disk then you should enable caching in DisplayImageOptions this way:

// Create default options which will be used for every 
//  displayImage(...) call if no options will be passed to this method
DisplayImageOptions defaultOptions = new DisplayImageOptions.Builder()
   		...
           .cacheInMemory(true)
           .cacheOnDisk(true)
           ...
           .build();
ImageLoaderConfiguration config = new ImageLoaderConfiguration.Builder(getApplicationContext())
           ...
           .defaultDisplayImageOptions(defaultOptions)
           ...
           .build();
ImageLoader.getInstance().init(config); // Do it on Application start

// Then later, when you want to display image
ImageLoader.getInstance().displayImage(imageUrl, imageView); // Default options will be used

or this way:

DisplayImageOptions options = new DisplayImageOptions.Builder()
   		...
           .cacheInMemory(true)
           .cacheOnDisk(true)
           ...
           .build();
ImageLoader.getInstance().displayImage(imageUrl, imageView, options); // Incoming options will be used

2. If you enabled disk caching then UIL try to cache images on external storage (/sdcard/Android/data/[package_name]/cache). If external storage is not available then images are cached on device's filesystem. To provide caching on external storage (SD card) add following permission to AndroidManifest.xml:

<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" android:maxSdkVersion="18" />

3. How UIL define Bitmap size needed for exact ImageView? It searches defined parameters:

• Get actual measured width and height of ImageView
• Get android:layout_width and android:layout_height parameters
• Get android:maxWidth and/or android:maxHeight parameters
• Get maximum width and/or height parameters from configuration (memoryCacheExtraOptions(int, int) option)
• Get width and/or height of device screen

So try to set android:layout_width|android:layout_height or android:maxWidth|android:maxHeight parameters for ImageView if you know approximate maximum size of it. It will help correctly compute Bitmap size needed for this view and save memory.

4. If you often got OutOfMemoryError in your app using Universal Image Loader then:

• Disable caching in memory. If OOM is still occurs then it seems your app has a memory leak. Use MemoryAnalyzer to detect it. Otherwise try the following steps (all of them or several):
• Reduce thread pool size in configuration (.threadPoolSize(...)). 1 - 5 is recommended.
• Use .bitmapConfig(Bitmap.Config.RGB_565) in display options. Bitmaps in RGB_565 consume 2 times less memory than in ARGB_8888.
• Use .imageScaleType(ImageScaleType.EXACTLY)
• Use .diskCacheExtraOptions(480, 320, null) in configuration

5. For memory cache configuration (ImageLoaderConfiguration.memoryCache(...)) you can use already prepared implementations.

• Cache using only strong references:
  • LruMemoryCache (Least recently used bitmap is deleted when cache size limit is exceeded) - Used by default
• Caches using weak and strong references:
  • UsingFreqLimitedMemoryCache (Least frequently used bitmap is deleted when cache size limit is exceeded)
  • LRULimitedMemoryCache (Least recently used bitmap is deleted when cache size limit is exceeded)
  • FIFOLimitedMemoryCache (FIFO rule is used for deletion when cache size limit is exceeded)
  • LargestLimitedMemoryCache (The largest bitmap is deleted when cache size limit is exceeded)
  • LimitedAgeMemoryCache (Decorator. Cached object is deleted when its age exceeds defined value)
• Cache using only weak references:
  • WeakMemoryCache (Unlimited cache)

6. For disk cache configuration (ImageLoaderConfiguration.diskCache(...)) you can use already prepared implementations:

• UnlimitedDiscCache (The fastest cache, doesn't limit cache size) - Used by default
• LruDiskCache (Cache limited by total cache size and/or by file count. If cache size exceeds specified limit then least-recently used file will be deleted)
• LimitedAgeDiscCache (Size-unlimited cache with limited files' lifetime. If age of cached file exceeds defined limit then it will be deleted from cache.)

NOTE: UnlimitedDiscCache is pretty faster than other limited disk cache implementations.

7. To display bitmap (DisplayImageOptions.displayer(...)) you can use already prepared implementations:

• RoundedBitmapDisplayer (Displays bitmap with rounded corners)
• FadeInBitmapDisplayer (Displays image with "fade in" animation)

8. To avoid list (grid, ...) scrolling lags you can use PauseOnScrollListener:

boolean pauseOnScroll = false; // or true
boolean pauseOnFling = true; // or false
PauseOnScrollListener listener = new PauseOnScrollListener(imageLoader, pauseOnScroll, pauseOnFling);
listView.setOnScrollListener(listener);

9. If you see in logs some strange supplement at the end of image URL (e.g. http://anysite.com/images/image.png_230x460) then it doesn't mean this URL is used in requests. This is just "URL + target size", also this is key for Bitmap in memory cache. This postfix (_230x460) is NOT used in requests.

10. ImageLoader always keeps aspect ratio of images.