子类化 UIButton 但无法访问我的属性

问题描述

我创建了一个 UIButton 的子类:

I've created a sub class of UIButton:

//
//  DetailButton.h
#import <Foundation/Foundation.h>
#import <MapKit/MapKit.h>

@interface MyDetailButton : UIButton {
    NSObject *annotation;
}

@property (nonatomic, retain) NSObject *annotation;


@end

//
//  DetailButton.m
//


#import "MyDetailButton.h"


@implementation MyDetailButton


@synthesize annotation;

@end

我想我可以通过执行以下操作来创建这个对象并设置注释对象:

I figured that I can then create this object and set the annotation object by doing the following:

MyDetailButton* rightButton = [MyDetailButton buttonWithType:UIButtonTypeDetailDisclosure];
rightButton.annotation = localAnnotation;

localAnnotation 是一个 NSObject 但它实际上是一个 MKAnnotation.我不明白为什么这不起作用，但在运行时我收到此错误:

localAnnotation is an NSObject but it is really an MKAnnotation. I can't see why this doesn't work but at runtime I get this error:

 2010-05-27 10:37:29.214 DonorMapProto1[5241:207] *** -[UIButton annotation]: unrecognized selector sent to instance 0x445a190
2010-05-27 10:37:29.215 DonorMapProto1[5241:207] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '*** -[UIButton annotation]: unrecognized selector sent to instance 0x445a190'

'

我看不出它为什么要查看 UIButton，因为我已经对它进行了子类化，所以它应该查看 MyDetailButton 类来设置该注释属性.我是否错过了一些非常明显的事情.感觉是这样的:)

I can't see why it's even looking at UIButton because I've subclassed that so it should be looking at the MyDetailButton class to set that annotation property. Have I missed something really obvious. It feels like it :)

提前感谢您提供的任何帮助

Thanks in advance for any help you can provide

罗斯

推荐答案

UIButton 是一个类簇，这意味着苹果的 buttonWithType: 实现大概是这样的:

UIButton is a class cluster, which implies that Apple's implementation of buttonWithType: probably looks something like this:

+(id)buttonWithType:(UIButtonType)t {
  switch (t) {
    case UIButtonTypeDetailDisclosure:
      return [[[PrivateDetailDisclosureButtonClass alloc] init] autorelease];
    case ...
  }
}

因此，当您调用 [MyDetailButton buttonWithType:UIButtonTypeDetailDisclosure]; 时，您不会得到 MyDetailButton 的实例，而是会得到 PrivateDetailDisclosureButtonClass (或任何苹果实际称呼的).

So when you call [MyDetailButton buttonWithType:UIButtonTypeDetailDisclosure]; you don't get an instance of MyDetailButton, you get an instance of PrivateDetailDisclosureButtonClass (or whatever Apple actually calls it).

但是请注意，如果您使用 UIButtonTypeCustom 调用它，您可以让 buttonWithType 实例化一个子类(至少在模拟器运行v3.0):

Note, however, that you can get buttonWithType to instantiate a subclass if you call it with UIButtonTypeCustom (At least in the simulator running v3.0):

// LGButton is a straightforward subclass of UIButton
LGButton *testBtn = [LGButton buttonWithType:UIButtonTypeCustom];
LGButton *testBtn2 = [LGButton buttonWithType:UIButtonTypeDetailDisclosure];
NSLog(@"testBtn: %@, testBtn2: %@", [testBtn class], [testBtn2 class]);
// Output: testBtn: LGButton, testBtn2: UIButton

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