iOS绘图出现的错误

原文地址:点击打开链接 -(void)createCircle { CGPoint layerCenter = CGPointMake(CGRectGetWidth(self.view.frame)/2, CGRectGetWidth(self.view.frame)/2); CAShapeLayer *layer = [CAShapeLayer layer]; layer.frame = self.view.bounds; layer.lineWidth = 6.0; layer.strokeColor = [UIColor redColor].CGColor; layer.fillColor = [UIColor whiteColor].CGColor; self.path = [UIBezierPath bezierPath]; [self.path addArcWithCenter:layerCenter radius:50 startAngle:0.0 endAngle:M_PI*2 clockwise:YES]; [self.path stroke]; [self.path fill]; layer.path = self.path.CGPath; [self.view.layer addSublayer:layer]; } 错误日志如下： Sep 9 16:09:01 Test1[28072] <Error>: CGContextSaveGState: invalid context 0x0. If you want to see the backtrace, please set CG_CONTEXT_SHOW_BACKTRACE environmental variable. Sep 9 16:09:01 Test1[28072] <Error>: CGContextSetLineWidth: invalid context 0x0. If you want to see the backtrace, please set CG_CONTEXT_SHOW_BACKTRACE environmental variable. Sep 9 16:09:01 Test1[28072] <Error>: CGContextSetLineJoin: invalid context 0x0. If you want to see the backtrace, please set CG_CONTEXT_SHOW_BACKTRACE environmental variable. Sep 9 16:09:01 Test1[28072] <Error>: CGContextSetLineCap: invalid context 0x0. If you want to see the backtrace, please set CG_CONTEXT_SHOW_BACKTRACE environmental variable. Sep 9 16:09:01 Test1[28072] <Error>: CGContextSetMiterLimit: invalid context 0x0. If you want to see the backtrace, please set CG_CONTEXT_SHOW_BACKTRACE environmental variable. Sep 9 16:09:01 Test1[28072] <Error>: CGContextSetFlatness: invalid context 0x0. If you want to see the backtrace, please set CG_CONTEXT_SHOW_BACKTRACE environmental variable. Sep 9 16:09:01 Test1[28072] <Error>: CGContextAddPath: invalid context 0x0. If you want to see the backtrace, please set CG_CONTEXT_SHOW_BACKTRACE environmental variable. Sep 9 16:09:01 Test1[28072] <Error>: CGContextDrawPath: invalid context 0x0. If you want to see the backtrace, please set CG_CONTEXT_SHOW_BACKTRACE environmental variable. Sep 9 16:09:01 Test1[28072] <Error>: CGContextRestoreGState: invalid context 0x0. If you want to see the backtrace, please set CG_CONTEXT_SHOW_BACKTRACE environmental variable. Sep 9 16:09:01 Test1[28072] <Error>: CGContextSaveGState: invalid context 0x0. If you want to see the backtrace, please set CG_CONTEXT_SHOW_BACKTRACE environmental variable. Sep 9 16:09:01 Test1[28072] <Error>: CGContextSetFlatness: invalid context 0x0. If you want to see the backtrace, please set CG_CONTEXT_SHOW_BACKTRACE environmental variable. Sep 9 16:09:01 Test1[28072] <Error>: CGContextAddPath: invalid context 0x0. If you want to see the backtrace, please set CG_CONTEXT_SHOW_BACKTRACE environmental variable. Sep 9 16:09:01 Test1[28072] <Error>: CGContextDrawPath: invalid context 0x0. If you want to see the backtrace, please set CG_CONTEXT_SHOW_BACKTRACE environmental variable. Sep 9 16:09:01 Test1[28072] <Error>: CGContextRestoreGState: invalid context 0x0. If you want to see the backtrace, please set CG_CONTEXT_SHOW_BACKTRACE environmental variable 上网查找错误的原因，大部分都说是IOS9适配问题，设置app的状态栏样式的使用使用了旧的方式在IOS9中不兼容。但是我的工程中并没有设置状态栏，并且按照其解决方法更改后也没有解决这个问题。后来看到这篇文章 H含金量 iOS绘图及贝塞尔曲线关键知识 才知道问题所在。

因为绘图不在drawRect:方法中操作导致绘图时没有当前的图形上下文(context)可设置。所以应该在drawRect:中执行图形绘制。修改后代码如下：

-(void)createCircle { CGPoint layerCenter = CGPointMake(CGRectGetWidth(self.view.frame)/2, CGRectGetWidth(self.view.frame)/2); CAShapeLayer *layer = [CAShapeLayer layer]; layer.frame = self.view.bounds; layer.lineWidth = 6.0; layer.strokeColor = [UIColor redColor].CGColor; layer.fillColor = [UIColor whiteColor].CGColor; self.path = [UIBezierPath bezierPath]; [self.path addArcWithCenter:layerCenter radius:50 startAngle:0.0 endAngle:M_PI*2 clockwise:YES]; // [self.path stroke]; // [self.path fill]; layer.path = self.path.CGPath; [self.view.layer addSublayer:layer]; [self.view setNeedsDisplay]; } - (void) drawRect:(CGRect)rect { [self.path stroke]; [self.path fill]; } 或者改成这样：

-(void)createCircle { CGPoint layerCenter = CGPointMake(CGRectGetWidth(self.view.frame)/2, CGRectGetWidth(self.view.frame)/2); CAShapeLayer *layer = [CAShapeLayer layer]; layer.frame = self.view.bounds; layer.lineWidth = 6.0; layer.strokeColor = [UIColor redColor].CGColor; layer.fillColor = [UIColor whiteColor].CGColor; self.path = [UIBezierPath bezierPath]; [self.path addArcWithCenter:layerCenter radius:50 startAngle:0.0 endAngle:M_PI*2 clockwise:YES]; layer.path = self.path.CGPath; UIGraphicsBeginImageContext(self.view.bounds.size); [self.path stroke]; [self.path fill]; UIGraphicsEndImageContext(); [self.view.layer addSublayer:layer]; } 这样就不会再出现错误了。其实我这里的path是UIBezierPath，可以直接去掉[self.path stroke];和[self.path fill];这两处的。