What does “Receiver type 'CALayer' for instance message is a forward declaration” mean here?

问题

I'm porting a block of code from an iOS4 project to iOS5 and I'm having some troubles with ARC. The code generates a PDF from a screen capture.

PDF Generation Code

UIView *captureView;
...
NSMutableData *pdfData = [NSMutableData data];
UIGraphicsBeginPDFContextToData(pdfData, captureView.bounds, nil);
UIGraphicsBeginPDFPage();
CGContextRef pdfContext = UIGraphicsGetCurrentContext();
[captureView.layer renderInContext:pdfContext];
UIGraphicsEndPDFContext();

The renderInContext line

[captureView.layer renderInContext:pdfContext];

generates the following error.

Automatic Reference Counting issue
Receiver type 'CALayer' for instance message is a forward declaration

Any ideas what is going on here?

回答1:

I was able to duplicate your problem. This is what fixed it for me.

Add QuartzCore.framework to your project and this line to your .m file.

#import <QuartzCore/QuartzCore.h>

来源：https://stackoverflow.com/questions/7813379/what-does-receiver-type-calayer-for-instance-message-is-a-forward-declaration