Objective-C语法之动态类型(isKindOfClass, isMemberOfClass,id)等

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发布时间：2019-06-26

本文共 4271 字，大约阅读时间需要 14 分钟。

对象在运行时获取其类型的能力称为内省。内省可以有多种方法实现。

判断对象类型

-(BOOL) isKindOfClass: classObj

判断是否是这个类或者这个类的子类的实例/ 判断是否是这个类的实例

-(BOOL) isMemberOfClass: classObj

我们试试这两个方法的使用。

1、新建Person类继承NSObject,新建Teacher类继承Person

1.1、新建Person类

[cpp]

#import 
        
             @interface Person : NSObject  {      NSString *name;  }  -(void)setName:(NSString*)n;    @end

[cpp]

#import "Person.h"    @implementation Person  -(void)setName:(NSString *)n  {      name = n;  }    @end

1.2新建Teacher类

[cpp]

#import "Person.h"    @interface Teacher : Person    -(void)teach;    @end

[cpp]

#import "Teacher.h"    @implementation Teacher  -(void)teach  {      NSLog(@"我教数学");  }  @end

1.3 我们先实验下isMemberOfClass方法。

[cpp]

NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];     Person *person = [[Person alloc] init];     Teacher *teacher = [[Teacher alloc] init];          //YES     if ([teacher isMemberOfClass:[Teacher class]]) {          NSLog(@"teacher Teacher类的成员");     }     //NO     if ([teacher isMemberOfClass:[Person class]]) {         NSLog(@"teacher Person类的成员");     }     //NO     if ([teacher isMemberOfClass:[NSObject class]]) {         NSLog(@"teacher NSObject类的成员");     }     [person release];     [teacher release];     [pool release];

打印结果：

2012-07-04 14:23:07.965 ObjectiveCTest[2460:f803] teacher Teacher类的成员

只有第一个判断打印出来，isMemberOfClass判断是否是属于这类的实例，是否跟父类有关系他不管。

1.4 isKindOfClass方法

[cpp]

NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];  Person *person = [[Person alloc] init];  Teacher *teacher = [[Teacher alloc] init];    //YES  if ([teacher isKindOfClass:[Teacher class]]) {      NSLog(@"teacher 是 Teacher类或Teacher的子类");  }  //YES  if ([teacher isKindOfClass:[Person class]]) {      NSLog(@"teacher 是 Person类或Person的子类");  }  //YES  if ([teacher isKindOfClass:[NSObject class]]) {      NSLog(@"teacher 是 NSObject类或NSObject的子类");  }  [person release];  [teacher release];  [pool release];

2012-07-04 14:34:17.315 ObjectiveCTest[2595:f803] teacher 是 Teacher类或Teacher的子类

2012-07-04 14:34:17.316 ObjectiveCTest[2595:f803] teacher 是 Person类或Person的子类

2012-07-04 14:34:17.316 ObjectiveCTest[2595:f803] teacher 是 NSObject类或NSObject的子类

三个结果都打印出来了。

2、

判读实例是否有这样方法

-(BOOL) respondsToSelector: selector

判断类是否有这个方法。此方法是类方法，不能用在类的对象

+(BOOL) instancesRespondToSelector:

2.1 respondsToSelector的使用

这里不写对象的创建和释放了，参考上面的代码

[cpp]

// YES  if ( [teacher respondsToSelector: @selector( setName: )] == YES ) {      NSLog(@"teacher responds to setSize: method" );  }    // NO  if ( [teacher respondsToSelector: @selector( abcde )] == YES ) {      NSLog(@"teacher responds to nonExistant method" );  }    // YES  if ( [teacher respondsToSelector: @selector( alloc )] == YES ) {      NSLog(@"teacher class responds to alloc method\n" );  }

打印结果：

2012-07-04 14:39:49.853 ObjectiveCTest[2723:f803] teacher responds to setSize: method

2012-07-04 14:39:49.854 ObjectiveCTest[2723:f803] teacher class responds to alloc method

中间的那个判断我随便写了个selector,当然没有了。respondsToSelector 检查类方法 alloc返回YES

2.2 instancesRespondToSelector

[cpp]

// NO      if ( [Person instancesRespondToSelector: @selector(teach)] == YES ) {          NSLog(@"Person instance responds to teach method" );      }            // YES      if ( [Teacher instancesRespondToSelector: @selector(teach)] == YES ) {          NSLog(@"Teacher instance responds to teach method");      }      // YES      if ( [Teacher instancesRespondToSelector: @selector(setName:)] == YES ) {          NSLog(@"Teacher instance responds to setName: method" );      }

打印结果：

[cpp]

2012-07-04 14:52:29.378 ObjectiveCTest[2961:f803] Teacher instance responds to teach method

2012-07-04 14:52:29.379 ObjectiveCTest[2961:f803] Teacher instance responds to setName: method

3、Objective-C的id类型

C++ 使用的是强类型：对象必须符合其类型，否则不能通过编译。在 Objective-C 中，id类型类似于(void*) ,可以指向任何类的实例。而不需要强制转换。

下面看看使用，

先把Teacher类中的 teach方法修改一下，改成

-(void)teach{    NSLog(@"%@ 教数学" ,name);}

然后实现并调用

[cpp]

NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];  Person *person = [[Person alloc] init];  Teacher *teacher = [[Teacher alloc] init];    id p = person;  id t = teacher;  [t setName:@"张三老师"];  [t teach];    [person release];  [teacher release];  [pool release];

打印结果：

[cpp]