UIView子类中的drawRect不会更新图像

Question

I have a UIView subclass that I would like to use to draw images with different blend modes.

code:

@implementation CompositeImageView

- (id)initWithFrame:(CGRect)frame
{
    self = [super initWithFrame:frame];
    if (self) {
        // Initialization code
    }
    return self;
}

-(void)setBlendMode:(CGBlendMode) composite
{
    blender = composite;
}

-(void)setImage:(UIImage*) img
{
    image = img;
}

- (void)drawRect:(CGRect)rect
{
    NSLog(@"it draws");
    CGContextRef c = UIGraphicsGetCurrentContext();
    CGContextSetBlendMode(c, blender);
    CGContextDrawImage(c, rect, image.CGImage);
}

@end

the code that I use to set it up it is:

[testImage setImage:[UIImage imageNamed:@"Prayer_Background_Paid"]];
[testImage setBlendMode:kCGBlendModeColor];
[testImage setNeedsDisplay];

I am using the interface builder to place a large rectangular UIView, and then set its class to CompositeImageView. However, it still draws as a large white square. Even if I comment out everything inside drawRect, it still draws the white square. However, it IS calling drawRect, because "it draws" is being logged.

Answer 1

Are you sure kCGBlendModeColor is what you want? From the Apple doc:

Uses the luminance values of the background with the hue and saturation values of the source image.

It seems that if it was a white background, the blended image would also appear white.