Android Development: Loading image

In a previous post I talked about loading bitmaps. In this post I will tell something about caching the loaded resources. For this I created a little util class. To give you an example how to use it here is the code. I will explain it step by step.

private Matrix scaleMatrix;

public UICard build(Card c, int color) {

	if (getBitmap(c, color) == null) {
		this.loadBitmap(c, color);
	}

	if (getBitmap(Card.Front, color) == null) {
		this.loadBitmap(Card.Front, color);
	}
	
	
	UICard card = new UICard(c, color);
	card.setBackImage(getBitmap(c, color));
	card.setFrontImage(getBitmap(Card.Front, color));
	return card;
}

private Bitmap getBitmap(Card c, int color) {
	LruCache<Card, Bitmap> cache = this.imageCacheRed;
	if (color == UICard.BLUE) {
		cache = this.imageCacheBlue;
	}
	return cache.get(c);
}

private void loadBitmap(Card c, int color) {
	int drawable = getRedDrawable(c);
	if (color == UICard.BLUE) {
		drawable = getBlueDrawable(c);
	}
	Bitmap cardImage = BitmapFactory.decodeResource(context.gtResources(),drawable);

	cardImage = Bitmap.createBitmap(cardImage, 0, 0, cardImage.getWidth(),cardImage.getHeight(), scaleMatrix, true);

	if (color == UICard.RED) {
		this.imageCacheRed.put(c, cardImage);
	} else {
		this.imageCacheBlue.put(c, cardImage);
	}
}	

private void init() {

	final int maxMemory = (int) (Runtime.getRuntime().maxMemory() / 1024);
	final int cacheSize = maxMemory / 4;
	this.imageCacheBlue = new LruCache<Card, Bitmap>(cacheSize) {
	@Override
	protected int sizeOf(Card key, Bitmap bitmap) {
		return (bitmap.getRowBytes() * bitmap.getHeight()) / 1024; 
		}
	};

	this.imageCacheRed = new LruCache<Card, Bitmap>(cacheSize) {

	@Override
	protected int sizeOf(Card key, Bitmap bitmap) {
		return (bitmap.getRowBytes() * bitmap.getHeight()) / 1024	}
	};

	Matrix m = new Matrix();
	m.preScale(0.1f, 0.1f);
	this.scaleMatrix = m;
}
}

When the View needs an image it calls the method ‘build’ (3).

It passes a Card object that specifies which card we want to load. We also need to tell the builder which color we need  ( two sides in this game remember? )

It will first check if bitmap belonging to the card specified already has been loaded in the past (20-26).  It therefore will get the correct cache (21-24) ( Yes I have 2 cache’s one for each side ). When the card has not been found in the cache it should be loaded (  5 and 6). Therefore we find the correct drawable (from the R object ) (29-32) and create a bitmap out of it (33-35). We scale it down using a scale matrix and we put the image back in the correct cache (37-41). After that we try to load it again (line 15-16).

By using this approach we asure the app that it will always be using the same instance of a particular bitmap.

I hope this will help you a bit developing your own game apps.