Question

I need to darken a UIImageView when it gets touched, almost exactly like icons on the springboard (home screen).

Should I be added UIView with a 0.5 alpha and black background. This seems clumsy. Should I be using Layers or something (CALayers).

Answer 1

How about subclassing UIView and adding a UIImage ivar (called image)? Then you could override -drawRect: something like this, provided you had a boolean ivar called pressed that was set while touched.

- (void)drawRect:(CGRect)rect
{
[image drawAtPoint:(CGPointMake(0.0, 0.0))];

// if pressed, fill rect with dark translucent color
if (pressed)
    {
    CGContextRef ctx = UIGraphicsGetCurrentContext();
    CGContextSaveGState(ctx);
    CGContextSetRGBFillColor(ctx, 0.5, 0.5, 0.5, 0.5);
    CGContextFillRect(ctx, rect);
    CGContextRestoreGState(ctx);
    }
}

You would want to experiment with RGBA values above. And, of course, non-rectangular shapes would require a bit more work – like a CGMutablePathRef.