Xamarin Android – Image Caching

adding-to-cache.cs

if (_memoryCache.Get(key) == null)
	_memoryCache.Put(key, bitmap);

cache-instantiation.cs

// Get max available VM memory, exceeding this amount will throw an OutOfMemory exception.
// Stored in kilobytes as LruCache takes an int in its constructor.
var maxMemory = (int)(Java.Lang.Runtime.GetRuntime().MaxMemory() / 1024);

// Use 1/8th of the available memory for this memory cache.
int cacheSize = maxMemory / 8;

_memoryCache = new MemoryLimitedLruCache(cacheSize);

memory-limited-lru-cache.cs

/// <summary>
/// LruCache limited by memory footprint in KB rather than number of items.
/// </summary>
public class MemoryLimitedLruCache : LruCache
{
	public MemoryLimitedLruCache(int size) : base(size) {}

	protected override int SizeOf(Java.Lang.Object key, Java.Lang.Object value)
	{
		// android.graphics.Bitmap.getByteCount() method isn't currently implemented in Xamarin. Invoke Java method.
		IntPtr classRef = JNIEnv.FindClass("android/graphics/Bitmap");
		var getBytesMethodHandle = JNIEnv.GetMethodID(classRef, "getByteCount", "()I");
		var byteCount = JNIEnv.CallIntMethod(value.Handle, getBytesMethodHandle);

		return byteCount / 1024;
	}
}