CALayer 子类“drawInContext”打电话但不画画？

发布于 2024-12-29 01:35:59 字数 546 浏览 1 评论 0原文

我正在尝试绘制 CALayer 子类。使用 setNeedsDisplay 调用 drawInContext，但没有绘制任何内容。这里做了什么/出了什么问题？

 - (void)drawInContext:(CGContextRef)ctx
{
    CGContextSetFillColorWithColor(ctx, [UIColor redColor].CGColor);
    [[UIBezierPath bezierPathWithRect:CGRectMake(100, 100, 100, 100)] fill];

    [@"Vowel" drawAtPoint:CGPointMake(0, 0) withFont:[UIFont fontWithName:@"Chalkboard" size:14]];
}

编辑我收到此错误：

CGContextAddPath：无效上下文 0x0

谢谢沙尼

原文

I am trying to draw in a CALayer subclass.
The drawInContext is called with setNeedsDisplay but nothing is drawn.
What am doing/getting wrong here ?

 - (void)drawInContext:(CGContextRef)ctx
{
    CGContextSetFillColorWithColor(ctx, [UIColor redColor].CGColor);
    [[UIBezierPath bezierPathWithRect:CGRectMake(100, 100, 100, 100)] fill];

    [@"Vowel" drawAtPoint:CGPointMake(0, 0) withFont:[UIFont fontWithName:@"Chalkboard" size:14]];
}

Edit
I am getting this error :

CGContextAddPath: invalid context 0x0

Thanks
Shani

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陌若浮生 2025-01-05 01:35:59

您正在混合 CG 调用和 UIKit 调用。 -[UIBezierPath fill] 和 -[NSString drawAtPoint:withFont:] 都绘制到 UIKit 上下文堆栈顶部的上下文中。这与传递到 -drawInContext: 的上下文不同。您应该将您的函数修改为如下所示：

- (void)drawInContext:(CGContextRef)ctx {
    UIGraphicsPushContext(ctx);
    [[UIColor redColor] setFill];
    [[UIBezierPath bezierPathWithRect:CGRectMake(100, 100, 100, 100)] fill];
    [@"Vowel" drawAtPoint:CGPointMake(0, 0) withFont:[UIFont fontWithName:@"Chalkboard" size:14]];
    UIGraphicsPopContext();
}

You're mixing CG calls and UIKit calls. -[UIBezierPath fill] and -[NSString drawAtPoint:withFont:] both draw into the context at the top of the UIKit context stack. That's not the same thing as the context passed into -drawInContext:. You should modify your function to look like:

- (void)drawInContext:(CGContextRef)ctx {
    UIGraphicsPushContext(ctx);
    [[UIColor redColor] setFill];
    [[UIBezierPath bezierPathWithRect:CGRectMake(100, 100, 100, 100)] fill];
    [@"Vowel" drawAtPoint:CGPointMake(0, 0) withFont:[UIFont fontWithName:@"Chalkboard" size:14]];
    UIGraphicsPopContext();
}

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