子类化UIButton但无法访问我的属性

Question

我创建了一个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

我想我可以通过执行以下操作创建此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,但在运行时我得到这个错误:

 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会查看UIButton,因为我已经将其子类化了,所以应该查看MyDetailButton类来设置该注释属性.我错过了一些非常明显的东西.感觉就像:)

提前感谢您提供的任何帮助

罗斯

Answer 1

UIButton是一个类集群,这意味着Apple的实现buttonWithType:可能看起来像这样:

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

因此,当你打电话给[MyDetailButton buttonWithType:UIButtonTypeDetailDisclosure];你时,你没有得到一个实例MyDetailButton,你会得到一个实例PrivateDetailDisclosureButtonClass(或者Apple实际上称之为的实例).

但是请注意,你可以得到buttonWithType,如果你把它实例化一个子类UIButtonTypeCustom(至少在模拟器中运行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