Iphone 如何在此方法中实现擦除/撤消

我已经成功地实现了touchesMoved，它正在正确地绘制线条。现在我在实现擦除方法时遇到了问题，请在我缺少的地方帮助我

- (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) Erase
{
    //NSSet *touches;
    //UITouch *touch; //= (NSSet *)[touch anyObject];   
    CGPoint currentPoint; //= [touch locationInView:self.view];
    currentPoint.y += 20;

    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();
    }

     mouseMoved--;

}

---

我已经成功地在moved Touchs中实现了擦除，但当我点击其中一个时，它会擦除，但在鼠标悬停并点击左键时，它会停止擦除。然后需要再次单击（轻触）以在新点擦除。那我怎么才能在移动的触摸上不断擦除

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

   if (eraseBtnSelected == YES) {

        if ([touch tapCount] == 1) {

            [self EraseButton];

        }
   }
}

---

不要在事件处理方法中绘制任何图形永远。使用它们编辑要绘制的内容列表，并在

-draw..

中进行所有绘制。像

-drawRect:

这样的方法

要删除某些内容，只需将其从要绘制的内容列表中删除，然后重新绘制有问题的视图或图层。

更改以下行

CGContextSetRGBStrokeColor(UIGraphicsGetCurrentContext(), 1.0, 0.0, 0.0, 1.0);

到

如果背景颜色为白色，则这行代码有效，如果其他颜色为白色，则这是一个问题

CGContextSetRGBStrokeColor(UIGraphicsGetCurrentContext(), 1.0, 1.0, 1.0, 1.0);

CGContextSetRGBStrokeColor(UIGraphicsGetCurrentContext(), 1.0, 1.0, 1.0, 1.0);