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我正在尝试调整绘图应用程序的苹果示例（使用触摸）以使用缩放视图而不是全屏视图，无论我尝试将图像缩放到不同大小时，线条都没有在正确的位置绘制，上我刷我的手指，它画得越低。

例如，如果我尝试在视图的下半部分绘制它可以很好地绘制手指触摸的线，如果我尝试在视图的上半部分绘制它会在我的手指触摸的位置绘制下面的线。

任何人都可以指出我应该改变什么以使代码正常工作？

如果我将下面的代码更改为 1004 而不是 500 一切正常）

我使用的代码是：

//CLASS IMPLEMENTATIONS:
- (void)viewDidLoad
{
[super viewDidLoad];
drawImage = [[UIImageView alloc] initWithImage:nil];
drawImage.frame = CGRectMake(0, 350, 768, 500);
drawImage.backgroundColor=[UIColor blackColor];
[self.view addSubview:drawImage];
self.view.backgroundColor = [UIColor lightGrayColor];
mouseMoved = 0;
// Do any additional setup after loading the view from its nib.
}
- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {

mouseSwiped = NO;
UITouch *touch = [touches anyObject];

if ([touch tapCount] == 2) {
    drawImage.image = nil;

    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);
[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, 350, 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();
}
}
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