清除上下文图形

Question

我正在尝试清除图形上下文。它使用这两种方式完美地清除。

 1. clearContextBeforeDrawing

 2. CGContextClearRect(context, rect);       
CGContextSetFillColorWithColor(context, [UIColor whiteColor].CGColor);       
CGContextFillRect(context, rect);                                                                          
CGContextFlush(context);

但是当我再次画线时。前面的行与出现点的新行混合在一起。有人可以帮忙吗？

这就是我清除线条的方式

-(IBAction)eraseButton:(id)sender
{
    self.viewmainHandwriting.isErase = TRUE;
    [self.viewmainHandwriting setBackgroundColor:[UIColor clearColor]];
    [self.viewmainHandwriting setNeedsDisplay]; //It calls my drawRect Function

}

- (void)drawRect:(CGRect)rect
{
    CGContextRef context = UIGraphicsGetCurrentContext();

    if (!self.isErase)
    {

        CGContextAddPath(context, path);
        CGContextSetLineCap(context, kCGLineCapRound);
        CGContextSetLineWidth(context, self.lineWidth);
        CGContextSetStrokeColorWithColor(context, self.lineColor.CGColor);

        CGContextStrokePath(context);

        self.empty = NO;
    }

    else
    {
       CGContextClearRect(context, self.bounds);
       path
       self.isErase = FALSE;

    }

}

我是如何绘制线条

- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {
    UITouch *touch = [touches anyObject];

    previousPoint1 = [touch previousLocationInView:self];
    previousPoint2 = [touch previousLocationInView:self];
    currentPoint = [touch locationInView:self];

    [self touchesMoved:touches withEvent:event];
}

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

    CGPoint point = [touch locationInView:self];

    /* check if the point is farther than min dist from previous */
    CGFloat dx = point.x - currentPoint.x;
    CGFloat dy = point.y - currentPoint.y;

    if ((dx * dx + dy * dy) < kPointMinDistanceSquared) {
        return;
    }


    previousPoint2 = previousPoint1;
    previousPoint1 = [touch previousLocationInView:self];
    currentPoint = [touch locationInView:self];

    CGPoint mid1 = midPoint(previousPoint1, previousPoint2);
    CGPoint mid2 = midPoint(currentPoint, previousPoint1);
    CGMutablePathRef subpath = CGPathCreateMutable();
    CGPathMoveToPoint(subpath, NULL, mid1.x, mid1.y);
    CGPathAddQuadCurveToPoint(subpath, NULL, previousPoint1.x, previousPoint1.y, mid2.x, mid2.y);
    CGRect bounds = CGPathGetBoundingBox(subpath);

    CGPathAddPath(path, NULL, subpath);
    CGPathRelease(subpath);

    CGRect drawBox = bounds;
    drawBox.origin.x -= self.lineWidth * 2.0;
    drawBox.origin.y -= self.lineWidth * 2.0;
    drawBox.size.width += self.lineWidth * 4.0;
    drawBox.size.height += self.lineWidth * 4.0;

    [self setNeedsDisplayInRect:drawBox];
}

Answer 1

在清除整个视图（path？）的方法中，您似乎没有清除eraseButton。

所以路径仍然包含整个旧图。只显示您调用setNeedsDisplayInRect:的部分（来自touchesMoved:内）。您可以通过再次绘制来显示旧图纸。

您应该在path

中创建新的eraseButton:（可能是ivar）

CGPathRelease(path);
path = CGPathCreateMutable();