检测 UIBezierPath 笔划上的触摸，而不是填充[重复]

可能的重复：
如何检查用户是否在 CGPath 附近点击？ https://stackoverflow.com/questions/1143704/how-can-i-check-if-a-user-tapped-near-a-cgpath

我从这里遵循苹果的指南

http://developer.apple.com/library/ios/#documentation/2DDrawing/Conceptual/DrawingPrintingiOS/BezierPaths/BezierPaths.html http://developer.apple.com/library/ios/#documentation/2DDrawing/Conceptual/DrawingPrintingiOS/BezierPaths/BezierPaths.html

尝试仅检测 UIBezierPath 的描边部分上的触摸事件。如果我使用 UIBezierPath 方法 containsPoint，它工作正常，但它会检测 UIBezierPath 的笔划和填充部分上的触摸事件，并且我希望它仅发生在笔划部分上。

按照 Apple 的指南（在链接的清单 3-6 中），我创建了这个函数：

- (BOOL)containsPoint:(CGPoint)point onPath:(UIBezierPath*)path inFillArea:(BOOL)inFill
{
    CGContextRef context = UIGraphicsGetCurrentContext();    
    CGPathRef cgPath = path.CGPath;    
    BOOL    isHit = NO;

    // Determine the drawing mode to use. Default to    
    // detecting hits on the stroked portion of the path.    
    CGPathDrawingMode mode = kCGPathStroke;    
    if (inFill)        
    {   
        // Look for hits in the fill area of the path instead.
        if (path.usesEvenOddFillRule)
            mode = kCGPathEOFill;
        else
            mode = kCGPathFill;
    }

    // Save the graphics state so that the path can be
    // removed later.
    CGContextSaveGState(context);
    CGContextAddPath(context, cgPath);

   // Do the hit detection.
   isHit = CGContextPathContainsPoint(context, point, mode);
   CGContextRestoreGState(context);
   return isHit;
}

当我调用它时，我得到：

错误：CGContextSaveGState：无效上下文 0x0
错误：CGContextAddPath：无效上下文 0x0
错误：CGContextPathContainsPoint：无效上下文 0x0
错误：CGContextRestoreGState：无效上下文 0x0

这是我的视图的 drawRect 函数，以及创建路径的代码：

- (UIBezierPath *) createPath {
    static UIBezierPath *path = nil;
    if(!path) {
        path = [[UIBezierPath bezierPathWithOvalInRect:CGRectMake(35, 45, 250, 250)] retain];
        path.lineWidth = 50.0;
        [path closePath];
    }    
    return path;
}

/*
// Only override drawRect: if you perform custom drawing.
// An empty implementation adversely affects performance during animation.
*/ 
- (void)drawRect:(CGRect)rect
{
    // Drawing code

    //draw a circle
    UIBezierPath *aPath = [self createPath];

    //set stroke width
    aPath.lineWidth = 50.0;

    //set stroke color
    [[UIColor blueColor] setStroke];

    //stroke path
    [aPath stroke];

    //close path
    [aPath closePath];

    //add a label at the "top"
    UILabel *topLabel;
    topLabel = [[UILabel alloc]initWithFrame:CGRectMake(120, -5, 80, 25)];
    topLabel.text = @"The Top";
    [self addSubview:topLabel];
}

然后我尝试调用 TouchMoved 内部的 containsPoint 函数，如下所示：

if (![self containsPoint:c onPath:[self createPath] inFillArea:NO]) return;

当您当前没有绘画时（如touchesMoved方法），没有当前上下文，所以UIGraphicsGetCurrentContext()将返回 NULL。

由于您对上下文所做的只是使用其当前路径，因此您也可以使用CGPathContainsPoint http://developer.apple.com/library/mac/documentation/GraphicsImaging/Reference/CGPath/Reference/reference.html#//apple_ref/c/func/CGPathContainsPoint代替CGContextPathContainsPoint.