Draw lines in a UIView, with transparent background - ios

Question

I have the following codes to draw lines in a UIView. But once I start drawing, the view becomes dark grey. How can I make the background transparent? I already set the backgroundColor to clearColor, but the background is still dark gray. What did I miss?
#interface CanvasView () {
UIColor *colorLine;
UIBezierPath *pathBezier;
}
#end
#implementation CanvasView
#synthesize imgCached;
- (id)initWithCoder:(NSCoder *)aDecoder {
self = [super initWithCoder:aDecoder];
if(self) {
self.backgroundColor = [UIColor clearColor];
[self setMultipleTouchEnabled:NO];
pathBezier = [[UIBezierPath alloc] init];
pathBezier.lineWidth = 5;
colorLine = [UIColor redColor];
}
return self;
}
- (void)drawRect:(CGRect)rect {
[self.imgCached drawInRect:rect];
[pathBezier stroke];
}
- (void)drawCache {
UIGraphicsBeginImageContextWithOptions(self.bounds.size, YES, 0.0);
[colorLine setStroke];
if(!self.imgCached) {
UIBezierPath *rectpath = [UIBezierPath bezierPathWithRect:self.bounds];
[rectpath fill];
}
[self.imgCached drawAtPoint:CGPointZero];
[pathBezier stroke];
self.imgCached = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
}
- (void)clearGraphics {
self.imgCached = nil;
[pathBezier removeAllPoints];
[self setNeedsDisplay];
}
#pragma mark - Touch methods
- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {
UITouch *touch = [[touches allObjects] objectAtIndex:0];
[pathBezier moveToPoint:[touch locationInView:self]];
}
- (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event {
UITouch *touch = [[touches allObjects] objectAtIndex:0];
[pathBezier addLineToPoint:[touch locationInView:self]];
[self setNeedsDisplay];
}
- (void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event {
UITouch *touch = [touches anyObject];
CGPoint p = [touch locationInView:self];
[pathBezier addLineToPoint:p];
[self drawCache];
[self setNeedsDisplay];
[pathBezier removeAllPoints];
}
- (void)touchesCancelled:(NSSet *)touches withEvent:(UIEvent *)event {
[self touchesEnded:touches withEvent:event];
}
p.s. the imgCached is:
#property (nonatomic, strong) UIImage *imgCached;

Answer 1

Replace your drawRect: and drawCache methods with the following:
- (void)drawRect:(CGRect)rect {
[self.imgCached drawInRect:rect];
[colorLine setStroke];
[pathBezier stroke];
}
- (void)drawCache {
UIGraphicsBeginImageContextWithOptions(self.bounds.size, NO, 0.0);
[colorLine setStroke];
[self.imgCached drawAtPoint:CGPointZero];
[pathBezier stroke];
self.imgCached = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
}