UILabel 子类偶尔会在绘制矩形上崩溃：

Question

所以我有一个 UILabel 子类，它只会在第一次加载时经常崩溃。该标签位于我的根视图控制器中，因此它是第一个加载的对象之一。问题是，它一直在drawRect中的一行上崩溃，我将在下面指出。

我尝试确保文本不为零，如果是，则跳过绘图，因为 sizeWithFont: 不断给我 NaN 错误，这会导致运行时崩溃。

如果您对 CoreGraphics 更有经验，请帮助我并告诉我为什么这个特定的代码片段不稳定：

- (void)drawRect:(CGRect)rect {
if(self.text == nil && self.text.length >! 0){
    return;
}
UIFont *font = self.font;
CGSize fontSize = [self.text sizeWithFont:font];
if(isnan(fontSize.width) == YES)return;
if(isnan(fontSize.height) == YES)return;
CGImageRef mask = [self createMaskWithSize:rect.size shape:^{
    [[UIColor blackColor] setFill];
    CGContextFillRect(UIGraphicsGetCurrentContext(), rect);
    [[UIColor whiteColor] setFill];
    // custom shape goes here
    if(self.textAlignment == UITextAlignmentLeft){
        [self.text drawAtPoint:CGPointMake(0, 0) withFont:font];
        [self.text drawAtPoint:CGPointMake(0, -1) withFont:font];
    }else{
        [self.text drawAtPoint:CGPointMake((self.bounds.size.width/2)-(fontSize.width/2), 0) withFont:font];
        [self.text drawAtPoint:CGPointMake((self.bounds.size.width/2)-(fontSize.width/2), -1) withFont:font];
    }
}];

CGImageRef cutoutRef = CGImageCreateWithMask([self blackSquareOfSize:rect.size].CGImage, mask);

UIImage *cutout = [UIImage imageWithCGImage:cutoutRef scale:[[UIScreen mainScreen] scale] orientation:UIImageOrientationUp]; 
    ^^ THIS IS WHAT CRASHES *******

CGImageRelease(cutoutRef);  

CGImageRef shadedMask = [self createMaskWithSize:rect.size shape:^{
    [[UIColor whiteColor] setFill];
    CGContextFillRect(UIGraphicsGetCurrentContext(), rect);
    CGContextSetShadowWithColor(UIGraphicsGetCurrentContext(), CGSizeMake(0, .5), 2.5f, [[UIColor colorWithWhite:0.0 alpha:0.8] CGColor]);
    [cutout drawAtPoint:CGPointZero];
}];

// create negative image
UIGraphicsBeginImageContextWithOptions(rect.size, NO, 0);
[[UIColor blackColor] setFill];
// custom shape goes here
if(self.textAlignment == UITextAlignmentLeft)[self.text drawAtPoint:CGPointMake(0, -1) withFont:font];
else [self.text drawAtPoint:CGPointMake((self.bounds.size.width/2)-(fontSize.width/2), -1) withFont:font];
UIImage *negative = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext(); 

CGImageRef innerShadowRef = CGImageCreateWithMask(negative.CGImage, shadedMask);
//CGImageRelease(shadedMask);
//UIImage *innerShadow = [UIImage imageWithCGImage:innerShadowRef scale:[[UIScreen mainScreen] scale] orientation:UIImageOrientationUp];
CGImageRelease(innerShadowRef);

//Draw Bevel
[[UIColor whiteColor] setFill];
if(self.textAlignment == UITextAlignmentLeft)[self.text drawAtPoint:CGPointMake(0, 0.0) withFont:font];
else [self.text drawAtPoint:CGPointMake((self.bounds.size.width/2)-(fontSize.width/2), 0.0) withFont:font];

// draw actual image
[self.textColor setFill];
if(self.textAlignment == UITextAlignmentLeft)[self.text drawAtPoint:CGPointMake(0, -0.5) withFont:font];
else [self.text drawAtPoint:CGPointMake((self.bounds.size.width/2)-(fontSize.width/2), -0.5) withFont:font];
// finally apply shadow
//[innerShadow drawAtPoint:CGPointZero];

}

谢谢！

Answer 1

你的测试 self.text 的条件似乎是错误的，

用下面的代码测试......

 - (void)drawRect:(CGRect)rect {
    if(self.text == nil ){
        return;
    }
    else if([self.text length] == 0){
    return;
    }
    .............
    .............
    }//Close of drawRect: