투명 배경이있는 UIView에 선 그리기

Question

다음 코드를 사용하여 UIView에 선을 그립니다. 그러나 그림 그리기를 시작하면보기가 진회색이됩니다. 배경을 투명하게 만들려면 어떻게해야합니까? backgroundColor을 이미 clearColor으로 설정했지만 배경은 여전히 ​​어두운 회색입니다. 내가 놓친 게 무엇입니까?

@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. imgCached은 다음과 같습니다

@property (nonatomic, strong) UIImage *imgCached; 

Answer 1

은 다음으로 drawRect: 및 drawCache 방법을 바꾸기 : 통화에서

- (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(); 
}