Black background in UIView? - ios

Question

I followed a tutorial online to draw in a subclassed UIView. The tutorial showed a UIView with a white background, I fixed this by simply changing the super's bg color. The problem is, when touches end, the background does not remain clear. I have no idea. I simply tried setting the fill color to [uicolor clearcolor]; unsuccessfully. Here is the code I am using:
#implementation CachedLIView
{
UIBezierPath *path;
UIImage *incrementalImage; // (1)
}
- (id)initWithCoder:(NSCoder *)aDecoder
{
if (self = [super initWithCoder:aDecoder])
{
[self setMultipleTouchEnabled:NO];
[self setBackgroundColor:[UIColor whiteColor]];
path = [UIBezierPath bezierPath];
[path setLineWidth:2.0];
}
return self;
}
- (void)drawRect:(CGRect)rect
{
[incrementalImage drawInRect:rect]; // (3)
[path stroke];
}
- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event
{
UITouch *touch = [touches anyObject];
CGPoint p = [touch locationInView:self];
[path moveToPoint:p];
}
- (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event
{
UITouch *touch = [touches anyObject];
CGPoint p = [touch locationInView:self];
[path addLineToPoint:p];
[self setNeedsDisplay];
}
- (void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event // (2)
{
UITouch *touch = [touches anyObject];
CGPoint p = [touch locationInView:self];
[path addLineToPoint:p];
[self drawBitmap]; // (3)
[self setNeedsDisplay];
[path removeAllPoints]; //(4)
}
- (void)touchesCancelled:(NSSet *)touches withEvent:(UIEvent *)event
{
[self touchesEnded:touches withEvent:event];
}
- (void)drawBitmap // (3)
{
UIGraphicsBeginImageContextWithOptions(self.bounds.size, NO, 0.0);
[[UIColor blackColor] setStroke];
if (!incrementalImage) // first draw; paint background white by ...
{
UIBezierPath *rectpath = [UIBezierPath bezierPathWithRect:self.bounds]; // enclosing bitmap by a rectangle defined by another UIBezierPath object
[[UIColor clearColor] setFill];
[rectpath fill]; // filling it with white
}
[incrementalImage drawAtPoint:CGPointZero];
[path stroke];
incrementalImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
}

Answer 1

Put the following in your view -(id) initWithFrame method:
self = [super initWithFrame:frame];
if (self) {
self.backgroundColor = [UIColor clearColor];
}
return self;
That way your view subclass will have a transparent background = no black when drawing using bezier, CGContext… methods or anything else.