Question

I have the following code (where an error appears):

.h file

#import <Foundation/Foundation.h>
@interface Unit : NSObject
{
    UIImageView *view;
    CGRect rect;
}

@property(readonly, assign) UIImageView *view;
@property(readwrite, assign) CGRect rect;

@end

.m file

#import "Unit.h"
@implementation Unit

@synthesize view;  //Error appears here
@synthesize rect;

@end

The error that appears is existing ivar 'view' for unsafe_unretained property 'view' must be __unsafe_unretained. What does this mean and how can I fix it?

Answer 1

In your example, you have used (readonly, assign), however because you have also explicitly created the ivar, you need to add the __unsafe_unretained qualifier (due to assign qualifier) as per Automatic Reference Counting documentation on property declarations.

#import <Foundation/Foundation.h>
@interface Unit : NSObject
{
    CGRect rect;
}

@property(readonly, assign) UIImageView *view;
@property(readwrite, assign) CGRect rect;

@end

Simply remove the ivar declaration, and the compiler will generate the correct ownership qualifier.