撤消CGContext行

Question

我知道这样的帖子被问了很多次，但我在谷歌和这个网站上搜索了很多次，都没有找到任何解决方案，这就是为什么我要贴这个问题。我想要撤消我绘制的CGContext线，而不使用UIBezierPath或其他任何东西。有什么办法吗？下面是我用来绘制的代码：

 - (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event {

UITouch *touch = [touches anyObject];
CGPoint currentPoint = [touch locationInView:mainImageView];

UIGraphicsBeginImageContext(mainImageView.frame.size);
[mainImageView.image drawInRect:CGRectMake(0, 0, mainImageView.frame.size.width, mainImageView.frame.size.height)];

CGContextSetLineCap(UIGraphicsGetCurrentContext(), kCGLineCapRound);
CGContextSetLineWidth(UIGraphicsGetCurrentContext(), dimension);

const CGFloat *components = CGColorGetComponents([color CGColor]);
CGContextSetRGBStrokeColor(UIGraphicsGetCurrentContext(), components[0], components[1], components[2], components[3]);

CGContextBeginPath(UIGraphicsGetCurrentContext());
CGContextMoveToPoint(UIGraphicsGetCurrentContext(), lastPoint.x, lastPoint.y);
CGContextAddLineToPoint(UIGraphicsGetCurrentContext(), currentPoint.x, currentPoint.y);
CGContextStrokePath(UIGraphicsGetCurrentContext());

mainImageView.image = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();

lastPoint = currentPoint;}

谢谢。

Answer 1

要添加撤消：

一旦图片被涂上，你就不能透露任何信息...

你要么必须在每次图像改变时保留图像的副本(大量的内存，尽管这可能通过只保留改变区域的副本来减少)，要么保留用户绘制步骤的记录，然后在撤消之后重播它们。

Answer 2

由于您正在绘制图像，因此您可以将图像置为空，可见的线条将消失。

mainImageView.image = NULL;
// Or
mainImageView.image = originalImage; // Where originalImage is your background if you're using one.

更新

- (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event {
    UITouch *touch = [touches anyObject];
    CGPoint currentPoint = [touch locationInView:mainImageView];

    UIGraphicsBeginImageContext(mainImageView.frame.size);

    CGContextSetLineCap(UIGraphicsGetCurrentContext(), kCGLineCapRound);
    CGContextSetLineWidth(UIGraphicsGetCurrentContext(), dimension);

    const CGFloat *components = CGColorGetComponents([color CGColor]);
    CGContextSetRGBStrokeColor(UIGraphicsGetCurrentContext(), components[0], components[1], components[2], components[3]);

    CGContextBeginPath(UIGraphicsGetCurrentContext());
    CGContextMoveToPoint(UIGraphicsGetCurrentContext(), lastPoint.x, lastPoint.y);
    CGContextAddLineToPoint(UIGraphicsGetCurrentContext(), currentPoint.x, currentPoint.y);
    CGContextStrokePath(UIGraphicsGetCurrentContext());

    // Add the line as a subView.
    [mainImageView addSubView:[[UIImageView alloc] initWithImage:UIGraphicsGetImageFromCurrentImageContext()]];
    UIGraphicsEndImageContext();

    lastPoint = currentPoint;

}

- (void)undoLastLine
{
    [mainImageView.subviews.lastObject removeFromSuperview];
}