CoreGraphics: Image Transparent Background

问题

I am trying to draw an image with a 2px transparent border:

CGContextRef context = UIGraphicsGetCurrentContext();

CGContextSetRGBFillColor(context, 1.0, 1.0, 1.0, 0.0);

CGContextAddRect(context, CGRectMake(0.0, 0.0, outputImageSize.width, outputImageSize.height));
CGContextDrawPath(context, kCGPathFill);


[image drawInRect:CGRectMake(2.0,
                             ((outputImageSize.height - userPhotoImageSize.height) / 2.0) +2.0,
                             userPhotoImageSize.width -4.0, 
                             userPhotoImageSize.height -4.0)];


UIImage *screenshot = UIGraphicsGetImageFromCurrentImageContext();

UIGraphicsEndImageContext();

It keeps getting black border (background)... =( Any ideas?

Solved, the uiimageview in which I set the image was simply black background =( The above code works!