objective-c - 子类化 UIButton 但无法访问我的属性

Question

我创建了 UIButton 的子类:

//
//  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

我认为我可以通过执行以下操作来创建该对象并设置注释对象:

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:

 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'

'

我不明白为什么它甚至要查看 UIButton，因为我已经对其进行了子类化，因此它应该查看 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。感觉就是这样:)

预先感谢您提供的任何帮助

罗斯

Answer 1

UIButton 是一个类簇，这意味着 Apple 的 buttonWithType: 实现可能如下所示:

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

因此，当您调用 [MyDetailButton buttonWithType:UIButtonTypeDetailDisclosure]; 时，您不会获得 MyDetailButton 的实例，而是获得 PrivateDetailDisclosureButtonClass 的实例>(或者苹果公司实际的称呼)。

但是请注意，如果使用 UIButtonTypeCustom 调用子类，您可以获得 buttonWithType 来实例化子类(至少在运行的模拟器中) 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