Cannot use respondsToSelector using ARC on Mac

最新推荐文章于 2019-07-30 13:49:39 发布

翻译最新推荐文章于 2019-07-30 13:49:39 发布 · 1.6k 阅读

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本文详细解析了在Objective-C ARC环境下调用respondsToSelector时出现的‘Automatic Reference Counting Issue’错误的原因及解决方案。通过示例代码，深入探讨了如何让协议遵循NSObject以解决此问题。

When I call respondsToSelector in an ARC environment, I get the following error message Automatic Reference Counting Issue No known instance method for selector respondsToSelector:

This is the header

#import <AppKit/AppKit.h>


@class MTScrollView;

@protocol MTScrollViewDelegate
-(void)scrollViewDidScroll:(MTScrollView *)scrollView;
@end


@interface MTScrollView : NSScrollView 
{

}

@property(nonatomic, weak) id<MTScrollViewDelegate>delegate;

@end

This is the implementation file

#import "MTScrollView.h"

@implementation MTScrollView

@synthesize delegate;


- (void)reflectScrolledClipView:(NSClipView *)aClipView
{
    [super reflectScrolledClipView:aClipView];

    if([delegate respondsToSelector:@selector(scrollViewDidScroll:)])
    {
        [delegate scrollViewDidScroll:self];
    }
}

@end

Any suggestions on why I am getting this error?

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edited Oct 29 '11 at 19:17

Jeff Kelley
11.9k 3 36 58

asked Oct 29 '11 at 19:07

David
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1 Answer

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up vote 115 down vote accepted

Make the protocol conform to NSObject

@protocol MTScrollViewDelegate <NSObject>

Otherwise the compiler doesn't think that the object will respond to NSObject messages like respondsToSelector, and will generate a warning. It will succeed at runtime without issues either way.