修正CGBitmapContextCreate iOS8上的错误

: CGBitmapContextCreateImage: 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.

Replying here since I had the exact same pixel format when I got this error. I hope this answer helps someone.

The reason it was failing, in my case, was that kCGImageAlphaLast isn't a permitted value anymore on iOS 8, although it works well on iOS 7. The 32 pbb, 8 bpc combination only allows kCGImageAlphaNoneSkip* and kCGImageAlphaPremultiplied* for the Alpha Info. Apparently this was a problem always, but wasn't enforced before iOS 8. Here's my solution:

- (CGBitmapInfo)normalizeBitmapInfo:(CGBitmapInfo)oldBitmapInfo {
    //extract the alpha info by resetting everything else
    CGImageAlphaInfo alphaInfo = oldBitmapInfo & kCGBitmapAlphaInfoMask;

    //Since iOS8 it's not allowed anymore to create contexts with unmultiplied Alpha info
    if (alphaInfo == kCGImageAlphaLast) {
        alphaInfo = kCGImageAlphaPremultipliedLast;
    }
    if (alphaInfo == kCGImageAlphaFirst) {
        alphaInfo = kCGImageAlphaPremultipliedFirst;
    }

    //reset the bits
    CGBitmapInfo newBitmapInfo = oldBitmapInfo & ~kCGBitmapAlphaInfoMask;

    //set the bits to the new alphaInfo
    newBitmapInfo |= alphaInfo;

    return newBitmapInfo;
}

In my case the failing piece of code looked like this, where imageRef is a CGImageRef of a PNG loaded from the app bundle:

CGContextRef bitmap = CGBitmapContextCreate(NULL,
                                                newRect.size.width,
                                                newRect.size.height,
                                                CGImageGetBitsPerComponent(imageRef),
                                                0,
                                                CGImageGetColorSpace(imageRef),
                                                CGImageGetBitmapInfo(imageRef));

Sources: http://stackoverflow.com/a/19345325/3099609

https://developer.apple.com/library/mac/DOCUMENTATION/GraphicsImaging/Conceptual/drawingwithquartz2d/dq_context/dq_context.html#//apple_ref/doc/uid/TP30001066-CH203-BCIBHHBB