检测UIBezierPath笔触上的触摸，而不是填充 [英] Detect touch on UIBezierPath stroke, not fill

问题描述

可能重复：

我从这里下载Apple的指南

I'm following Apple's guide from here

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

只尝试在我的UIBezierPath的描边部分检测触摸事件。如果我使用UIBezierPath方法，containsPoint，它工作正常，但它检测触摸事件的笔触和UIBezierPath的填充部分，我希望它只发生在抚摸部分。

to try and detect a touch event only on the stroked portion of my UIBezierPath. If I use the UIBezierPath method, containsPoint, it works fine, but it detects touch events on the stroke and the fill portion of the UIBezierPath, and I want it to only occur on the stroked portion.

按照苹果指南（链接列表3-6），我创建了此功能：

Following Apple's guide (at listing 3-6 of the link), I created this function:

- (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，我会得到：

When I call it, I get:

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：invalid context 0x0

Error: CGContextSaveGState: invalid context 0x0
Error: CGContextAddPath: invalid context 0x0
Error: CGContextPathContainsPoint: invalid context 0x0
Error: CGContextRestoreGState: invalid context 0x0

这是我的view的drawRect函数，我的代码创建我的路径：

Here's my view's drawRect function, and my code to create my path:

- (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];
}

然后我试图调用touchesMoved里面的containsPoint函数， ：

I'm then trying to call the containsPoint function inside of touchesMoved, like this:

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

推荐答案

touchesMoved 方法），没有当前上下文，因此 UIGraphicsGetCurrentContext（）将返回NULL。

When you're currently not drawing (as in the touchesMoved method), there is no current context, so UIGraphicsGetCurrentContext() will return NULL.

由于你使用的上下文是使用它的当前路径，你可以使用 CGPathContainsPoint CGContextPathContainsPoint 。

As all you're doing with the context is to use its current path, you could just as well use CGPathContainsPoint instead of CGContextPathContainsPoint.

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