请设置CG_CONTEXT_SHOW_BACKTRACE环境变量 [英] please set CG_CONTEXT_SHOW_BACKTRACE environmental variable

问题描述

尽管查看了3个以上的帖子（2015年制作），但都没有解决我的问题。

Despite looking over more than 3 post (made in 2015) about this problem, non have solved mine.

每次运行时，都会绘制一个简单的代码一行使用UIBezierPath的程序将向我返回：

When ever I run, a simple, code to draw a line using UIBezierPath the program would return me this:

：CGContextSetStrokeColorWithColor：无效上下文0x0。如果您
要查看回溯，请设置CG_CONTEXT_SHOW_BACKTRACE
环境变量。

: CGContextSetStrokeColorWithColor: invalid context 0x0. If you want to see the backtrace, please set CG_CONTEXT_SHOW_BACKTRACE environmental variable.

：CGContextSetFillColorWithColor：无效上下文0x0。如果您
要查看回溯，请设置CG_CONTEXT_SHOW_BACKTRACE
环境变量。

: CGContextSetFillColorWithColor: invalid context 0x0. If you want to see the backtrace, please set CG_CONTEXT_SHOW_BACKTRACE environmental variable.

：CGContextSaveGState：无效上下文0x0。如果要查看
的回溯，请设置CG_CONTEXT_SHOW_BACKTRACE环境
变量。

: CGContextSaveGState: invalid context 0x0. If you want to see the backtrace, please set CG_CONTEXT_SHOW_BACKTRACE environmental variable.

：CGContextSetLineWidth：无效上下文0x0。如果要
查看回溯，请设置CG_CONTEXT_SHOW_BACKTRACE环境
变量。

: CGContextSetLineWidth: invalid context 0x0. If you want to see the backtrace, please set CG_CONTEXT_SHOW_BACKTRACE environmental variable.

：CGContextSetLineJoin：无效上下文0x0。如果要查看
的回溯，请设置CG_CONTEXT_SHOW_BACKTRACE环境
变量。

: CGContextSetLineJoin: invalid context 0x0. If you want to see the backtrace, please set CG_CONTEXT_SHOW_BACKTRACE environmental variable.

：CGContextSetLineCap：无效上下文0x0。如果要查看
的回溯，请设置CG_CONTEXT_SHOW_BACKTRACE环境
变量。

: CGContextSetLineCap: invalid context 0x0. If you want to see the backtrace, please set CG_CONTEXT_SHOW_BACKTRACE environmental variable.

：CGContextSetMiterLimit：无效上下文0x0。如果要
查看回溯，请设置CG_CONTEXT_SHOW_BACKTRACE环境
变量。

: CGContextSetMiterLimit: invalid context 0x0. If you want to see the backtrace, please set CG_CONTEXT_SHOW_BACKTRACE environmental variable.

：CGContextSetFlatness：无效上下文0x0。如果要查看
的回溯，请设置CG_CONTEXT_SHOW_BACKTRACE环境
变量。

: CGContextSetFlatness: invalid context 0x0. If you want to see the backtrace, please set CG_CONTEXT_SHOW_BACKTRACE environmental variable.

：CGContextAddPath：无效上下文0x0。如果要查看
的回溯，请设置CG_CONTEXT_SHOW_BACKTRACE环境
变量。

: CGContextAddPath: invalid context 0x0. If you want to see the backtrace, please set CG_CONTEXT_SHOW_BACKTRACE environmental variable.

：CGContextDrawPath：无效上下文0x0。如果要查看
的回溯，请设置CG_CONTEXT_SHOW_BACKTRACE环境
变量。

: CGContextDrawPath: invalid context 0x0. If you want to see the backtrace, please set CG_CONTEXT_SHOW_BACKTRACE environmental variable.

：CGContextRestoreGState：无效上下文0x0。如果要
看到回溯，请设置CG_CONTEXT_SHOW_BACKTRACE环境
变量。

: CGContextRestoreGState: invalid context 0x0. If you want to see the backtrace, please set CG_CONTEXT_SHOW_BACKTRACE environmental variable.

@interface line : UIView
UIBezierPath *myPath;
.........
@implementation
- (void) touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {
UITouch *touch = [[event allTouches]anyObject];
CGPoint touchLocation = [touch locationInView:self];
myPath = [UIBezierPath bezierPath];
[myPath moveToPoint:touchLocation];
}
- (void) touchesMoved:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event {
UITouch *touch = [[event allTouches]anyObject];
CGPoint touchLocation = [touch locationInView:self];
[myPath addLineToPoint:touchLocation];
[[UIColor blackColor]setStroke];
[[UIColor greenColor]setFill];
[myPath stroke];
}

如果我要使用drawRect绘制

If I was to draw using drawRect

- (void) drawRect:(CGRect)rect {
....
}

不会弹出错误。我想知道是否由于 touchesBegan 和 touchesMoved 无法执行绘制而收到这些错误？

No error would pop up. I was wondering If I was receiving these errors because touchesBegan and touchesMoved can't perform drawing?

在可可（OS X）中，我曾经使用 setNeedsDisplay ，但在可可触摸中并不存在。

In cocoa (OS X) I used to use setNeedsDisplay, but it doesn't exist in cocoa touch.

我要问的是，是否有消除这些错误的方法，或者还有另一种在运行时绘制 UIBezierPath 的方法。 / p>

All I'm asking is, is there anyway to remove these errors or is there another way to draw UIBezierPath during run time.

推荐答案

发生无效的上下文错误，因为您尝试使用 drawRect：方法，因此没有设置当前图形上下文。

Invalid context errors happen, because you are trying to use drawing operations outside of drawRect: method, so no current graphic context is set.

就像在OS X上一样，您应该在 drawRect：方法，然后使用 setNeedsDisplay 更新生成的图像。 setNeedsDisplay 和 setNeedsDisplayInRect：方法都可用于iOS上的UIView。

Like on OS X, you should perform drawing in drawRect: method, and use setNeedsDisplay to update resulting image. And both setNeedsDisplay and setNeedsDisplayInRect: methods are available for UIView on iOS.

因此，结果应如下所示：

So, result should look like this:

- (void) touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {
UITouch *touch = [[event allTouches]anyObject];
CGPoint touchLocation = [touch locationInView:self];
myPath = [UIBezierPath bezierPath];
[myPath moveToPoint:touchLocation];
}

- (void) touchesMoved:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event {
UITouch *touch = [[event allTouches]anyObject];
CGPoint touchLocation = [touch locationInView:self];
[myPath addLineToPoint:touchLocation];
[self setNeedsDisplay];
}

- (void) drawRect:(CGRect)rect {
[[UIColor blackColor]setStroke];
[[UIColor greenColor]setFill];
[myPath stroke];
}

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