升级到Xcode 4.2之后为什么MKAnnotation会显示警告

Question

在Xcode 4.1中没有问题，但升级到Xcode 4.2我收到以下警告：

Property 'title' 'copy' attribute does not match the property inherited from 'MKAnnotation'
Property 'subtitle' 'copy' attribute does not match the property inherited from 'MKAnnotation'

我的代码：

@interface MyAnnotation : NSObject <MKAnnotation> {
    CLLocationCoordinate2D coordinate;
    NSString *subtitle;  
    NSString *title; 
}
@property (nonatomic, readonly) CLLocationCoordinate2D coordinate;
@property (nonatomic, retain) NSString *subtitle;  
@property (nonatomic, retain) NSString *title; 

-(id)initWithCoordinate:(CLLocationCoordinate2D) coordinate;

@end

Answer 1

将其更改为：

@property (nonatomic, copy) NSString *subtitle;
@property (nonatomic, copy) NSString *title;

MKAnnotation协议声明

@property (nonatomic, readonly, copy) NSString *title;
@property (nonatomic, readonly, copy) NSString *subtitle;

您不应更改属性的存储类型，如果需要，您可以/应该进行的唯一更改是从readonly到readwrite;

Answer 2

尝试使用Edit -> Refactor -> Convert to Objective-C ARC

将您的应用转换为ARC