CGContext invalid context 0x0

Question

I am drawing into CGlayers, So I am creating the Layer and drawing the Layer into graphics context in drawRect method, this way

- (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);       

}

I do all the drawing operations in my touchesMoved function

-(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];
}

But when I start drawing, I get the error messages for all the CGContext functions used in touches moved, of which I am listing a few below.

<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.

1. I know the error is because, the Layer is not created yet, and because of that, I get this error, but then Layer should be created in drawRect method only because, its where the graphics context is alive.
2. If I call [self setNeedsDisplay]first and then my drawing functions, and again at last [self setNeedsDisplay], then everything works fine, with no errors, but I dont think, or rather dont know wheteher this is the right thing to do.

Answer 1

In your -touchesMoved:withEvent: method, just return if you don’t have a layer yet. The user can’t draw if they can’t see your view, after all. i.e. add

 if (!self.currentDrawingLayer)
   return;

at the top.