免费手绘不工作UIImageview

Question

我正在我的iPhone应用程序中绘制自由手绘图，并在主视图中将UIImageView作为子视图。当我在视图上绘制线条时，它在主视图上工作正常，但是当我尝试在图像视图上绘制时，它无效。我使用下面的代码绘制线条：

    - (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event
    {
      if([appdel.drawtype isEqualToString:@"pen"])
      {
        UITouch *touch = [touches anyObject];

        if ([touch tapCount] == 2)
        {
            img.image = nil;
            return;
        }

    lastPoint = [touch locationInView:self.view];
    lastPoint.y -= 20;
   }
 }

- (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event
{
    if([appdel.drawtype isEqualToString:@"pen"])
   {
    UITouch *touch = [touches anyObject];
    CGPoint currentPoint = [touch locationInView:self.view];
    currentPoint.y -= 20;


    UIGraphicsBeginImageContext(self.view.frame.size);
    [img.image drawInRect:CGRectMake(0, 0, self.view.frame.size.width, self.view.frame.size.height)];
    CGContextSetLineCap(UIGraphicsGetCurrentContext(), kCGLineCapRound);
    CGContextSetLineWidth(UIGraphicsGetCurrentContext(), 5.0);
    CGContextSetRGBStrokeColor(UIGraphicsGetCurrentContext(), 1.0, 0.0, 0.0, 1.0);
    CGContextBeginPath(UIGraphicsGetCurrentContext());
    CGContextMoveToPoint(UIGraphicsGetCurrentContext(), lastPoint.x, lastPoint.y);
    CGContextAddLineToPoint(UIGraphicsGetCurrentContext(), currentPoint.x, currentPoint.y);
    CGContextStrokePath(UIGraphicsGetCurrentContext());
    img.image = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();

    lastPoint = currentPoint;
    }

}

- (void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event
{
    if([appdel.drawtype isEqualToString:@"pen"])
   {
       UITouch *touch = [touches anyObject];

       if ([touch tapCount] == 2) {
           img.image = nil;
            return;
       }

        UIGraphicsBeginImageContext(self.view.frame.size);
        [img.image drawInRect:CGRectMake(0, 0, self.view.frame.size.width, self.view.frame.size.height)];
        CGContextSetLineCap(UIGraphicsGetCurrentContext(), kCGLineCapRound);
        CGContextSetLineWidth(UIGraphicsGetCurrentContext(), 5.0);
        CGContextSetRGBStrokeColor(UIGraphicsGetCurrentContext(), 1.0, 0.0, 0.0, 1.0);
        CGContextMoveToPoint(UIGraphicsGetCurrentContext(), lastPoint.x, lastPoint.y);
        CGContextAddLineToPoint(UIGraphicsGetCurrentContext(), lastPoint.x, lastPoint.y);
        CGContextStrokePath(UIGraphicsGetCurrentContext());
        CGContextFlush(UIGraphicsGetCurrentContext());
        img.image = UIGraphicsGetImageFromCurrentImageContext();
        UIGraphicsEndImageContext();

   }

}

如何在UIImageView图片上绘制线条？