Can't compile code when working with CALayer

问题:

For some reason I get linker errors when I try and use CALayer:

  "_OBJC_CLASS_$_CALayer", referenced from:

I have imported the following headers:

#import <Foundation/Foundation.h>
#import <UIKit/UIKit.h>
#import <QuartzCore/QuartzCore.h>

Code:

arrowImage = [[CALayer alloc] init];

回答1:

Make sure you also add the QuartzCore framework to your target. Just importing the header isn't enough.

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