Tracking Down Drawing Errors

Do you sometimes see this in your code while performing custom drawing using drawRect?

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<Error>: CGContextSaveGState: invalid context 0x0
<Error>: CGContextSetBlendMode: invalid context 0x0
<Error>: CGContextSetAlpha: invalid context 0x0
<Error>: CGContextTranslateCTM: invalid context 0x0
<Error>: CGContextScaleCTM: invalid context 0x0
<Error>: CGContextDrawImage: invalid context 0x0
<Error>: CGContextRestoreGState: invalid context 0x0

And as always is very hard to track, because you cannot exactly say which draw command actually cause this or where does it comes from. But there is a simple solution to this:

Use this symbolic breakpoint CGPostError in your xcode to stop executing on exact line where drawing error appears.

Now you can see all callstack and all values to find root cause of incorrect drawing.