Question

我正在绘制CGlayers，所以我在drawRect方法中创建Layer并将Layer绘制到图形上下文中，这样

- (void)drawRect:(CGRect)rect
{              
     CGContextRef context = UIGraphicsGetCurrentContext();
     if(self.currentDrawingLayer == nil)
     {
         CGLayerRef layer = CGLayerCreateWithContext(context, bounds.size, NULL);   
          self.currentDrawingLayer = layer;
     }                  

     CGContextDrawLayerInRect(context, self.bounds, self.currentDrawingLayer);       

}

我在touchesMoved函数中执行所有绘图操作

-(void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event
{
      CGContextRef layerContext =  CGLayerGetContext(self.currentDrawingLayer);

      CGContextSetLineCap(layerContext, kCGLineCapRound);
      CGContextSetLineJoin(layerContext, kCGLineJoinRound);
      CGContextSetAllowsAntialiasing(layerContext, YES);
      CGContextSetShouldAntialias(layerContext, YES);
      CGContextSetBlendMode(layerContext,kCGBlendModeClear);
      CGContextSetLineWidth(layerContext, self.eraseWidth);
      CGContextBeginPath(layerContext);
      CGContextAddPath(layerContext, mutablePath);
      CGContextStrokePath(layerContext);
      CGPathRelease(mutablePath);

      [self setNeedsDisplay];
}

但是当我开始绘图时，我得到移动触摸中使用的所有CGContext函数的错误消息，我在下面列出了几个。

<Error>: CGContextBeginPath: 
 This is a serious error. This application, or a library it uses, is using an invalid context  and is thereby contributing to an overall degradation of system stability and reliability. This notice is a courtesy: please fix this problem. It will become a fatal error in an upcoming update.
<Error>: CGContextAddPath: invalid context 0x0. This is a serious error. This application, or a library it uses, is using an invalid context  and is thereby contributing to an overall degradation of system stability and reliability. This notice is a courtesy: please fix this problem. It will become a fatal error in an upcoming update.

我知道错误是因为，还没有创建Layer，因此，我得到了这个错误，但是应该只在drawRect方法中创建Layer，因为它是图形上下文存活的地方。
如果我首先调用[self setNeedsDisplay]然后再调用我的绘图函数，再次调用[self setNeedsDisplay]，那么一切正常，没有错误，但我不认为，或者更确切地说不知道这是什么正确的事情。

Answer 1

在-touchesMoved:withEvent:方法中，如果您还没有图层，请返回。毕竟，如果用户无法看到您的视图，则无法进行绘制。即添加

 if (!self.currentDrawingLayer)
   return;

在顶部。

CGContext无效上下文0x0

1 个答案: