在类别界面/实现中设置新属性

问题描述

好，所以我有这个，但是它行不通:

Ok, so I have this, but it wont work:

@interface UILabel (touches)

@property (nonatomic) BOOL isMethodStep;

@end


@implementation UILabel (touches)

-(BOOL)isMethodStep {
    return self.isMethodStep;
}

-(void)setIsMethodStep:(BOOL)boolean {
    self.isMethodStep = boolean;
}

-(void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {
    if(self.isMethodStep){
        // set all labels to normal font:
        UIFont *toSet = (self.font == [UIFont fontWithName:@"Helvetica" size:16]) ? [UIFont fontWithName:@"Helvetica-Bold" size:16] : [UIFont fontWithName:@"Helvetica" size:16];

        id superView = self.superview;
        for(id theView in [(UIView *)superView subviews])
            if([theView isKindOfClass:[UILabel class]])
                [(UILabel *)theView setFont:[UIFont fontWithName:@"Helvetica" size:16]];

        self.font = toSet;
    }
}

@end

如果我取出getter和setter方法，那么它不起作用，它告诉我我需要创建一些getter和setter方法(或使用@synthesize-但将@synthesize放在@implementation中也会引发错误).但是使用getter和setter方法，我得到一个EXC_BAD_ACCESS和一个崩溃.有任何想法吗?谢谢

If I take out the getter and setter methods then it doesn't work it tells me I need to create some getter and setter methods (or use @synthesize - but putting @synthesize in the @implementation throws an error too). But with the getter and setter methods I get an EXC_BAD_ACCESS and a crash. Any ideas? Thanks

汤姆

推荐答案

不可能通过类别(仅方法)将成员和属性添加到现有类中.

It is not possible to add members and properties to an existing class via a category — only methods.

https://developer.apple .com/library/content/documentation/General/Conceptual/DevPedia-CocoaCore/Category.html

一个可能的解决方法是编写"setter/getter-like"方法，该方法使用单例来保存变量，而该方法原来是成员.

One possible workaround is to write "setter/getter-like" methods, that uses a singleton to save the variables, that would had been the member.

-(void)setMember:(MyObject *)someObject
{
    NSMutableDictionary *dict = [MySingleton sharedRegistry];
    [dict setObject:someObject forKey:self];
}

-(MyObject *)member
{
    NSMutableDictionary *dict = [MySingleton sharedRegistry];
    return [dict objectforKey:self];
}

或-当然-写一个自定义类，该类继承自UILabel

or — of course — write a custom class, that inherits from UILabel

请注意，现在可以在运行时注入关联对象. Objective C编程语言:关联引用

Note that nowadays an associated object can be injected during runtime. The Objective C Programming Language: Associative References

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