UIView drawInRect with UIImage results in blackbackground - iphone

Question

I have this following codes:
#implementation MyImageView
#synthesize image; //image is a UIImage
- (id)initWithFrame:(CGRect)frame
{
self = [super initWithFrame:frame];
if (self) {
// Initialization code
}
return self;
}
-(void) removeFromSuperview
{
self.image = nil;
[super removeFromSuperview];
}
- (void)drawRect:(CGRect)rect
{
// Drawing code
if (self.image)
{
CGContextRef context = UIGraphicsGetCurrentContext();
CGContextClearRect(context, rect);
//the below 2 lines is to prove that the alpha channel of my UIImage is indeed drawn
//CGContextSetFillColorWithColor(context, [UIColor whiteColor].CGColor);
//CGContextFillRect(context, rect);
CGContextDrawImage(context, self.bounds, self.image.CGImage);
}
}
#end
When I ran the code, I realized that the background of my view is black. To test if it was a problem with my UIImage, I used the 2 lines commented after CGContextClearRect(context, rect). Indeed a white background was drawn. Is there anyway for me to remove the black background? When I init MyImageView, i have already set backgroundColor to [UIColor clearColor].
Any advice is much appreciated.
Thanks

Answer 1

Setting the background color to [UIColor clearColor] should work. Also set self.opaque = NO to enable transparency.
You should also check that the correct initializer is being called. For example if the view is part of a XIB file, you need to implement initWithCoder: as well as initWithFrame: etc.

Answer 2

I had the same issue - this worked for me (Swift example)
var backgroundImage = UIImage() //background image - size = 100x100
var frontImage = UIImage() //smaller image to be drawn in the middle
UIGraphicsBeginImageContextWithOptions(CGSizeMake(100, 100), false, 0.0) //false here indicates transparent
var context = UIGraphicsGetCurrentContext()!
UIGraphicsPushContext(context)
backgroundImage.drawInRect(CGRectMake(0, 0, 100, 100))
frontImage.drawInRect(CGRectMake((100 - frontImage.size.width) / 2, (diameter - frontImage.size.height) / 2, frontImage.size.width, frontImage.size.height))
UIGraphicsPopContext()
var outputImage = UIGraphicsGetImageFromCurrentImageContext()
UIGraphicsEndImageContext()

Answer 3

Your CGContext will draw upside down
anyhow, so just go the easy route and use
[self.image drawInRect:CGRectMake(rect)];
Instead.