如何在 Objective C 中的 pdf 文件页面上像徒手工具一样绘制图像？

Question

我已经应用了这个 链接使用 CGPDF 类在 ipad 上显示 pdf 文件，现在我需要在同一 pdf 文件的加载页面上绘制图像。我正在使用

- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event 
{
    mouseSwiped = NO;
    UITouch *touch = [touches anyObject];
    if ([touch tapCount] == 2) 
    {
        //drawImage.image = nil;
        [NSObject cancelPreviousPerformRequestsWithTarget:self];
        return;
    }
    lastPoint = [touch locationInView:self.view];
    lastPoint.y -= 20;
}

- (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event 
{
    mouseSwiped = YES;
    UITouch *touch = [touches anyObject];
    CGPoint currentPoint = [touch locationInView:self.view];
    currentPoint.y -= 20;

    UIGraphicsBeginImageContext(self.view.frame.size);
    //  CGFloat x = self.view.frame.size.width-100;
    //  CGFloat y = self.view.frame.size.height-100;

    //  [drawImage.image drawInRect:CGRectMake(0, 0, x, y)];
    [drawImage.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());
    drawImage.image = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();

    lastPoint = currentPoint;
    mouseMoved++;
    if (mouseMoved == 10) 
    {
        mouseMoved = 0;
    }
}

- (void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event 
{
    UITouch *touch = [touches anyObject];
    if ([touch tapCount] == 2) 
    {
        drawImage.image = nil;
        return;
    }
    if(!mouseSwiped) 
    {
        UIGraphicsBeginImageContext(self.view.frame.size);
        [drawImage.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());
        drawImage.image = UIGraphicsGetImageFromCurrentImageContext();
        UIGraphicsEndImageContext();
    }
}

徒手工具，如果我没有加载 pdf 文件，我可以在视图上绘制图像。但我无法覆盖 pdf 页面上的图像。有人可以帮我解决一些问题吗？

提前致谢。