OC中判断对象类型和对象是否拥有该方法的机制

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

-(BOOL) isMemberOfClass: classObj 判断是否是这个类的实例

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

#import <Foundation/Foundation.h>

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

@end

 

#import "Person.h"

@implementation Person
-(void)setName:(NSString *)n
{
    name = n;
}

@end

1.2新建Teacher类

#import "Person.h"

@interface Teacher : Person

-(void)teach;

@end

 

#import "Teacher.h"

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

1.3 我们先实验下isMemberOfClass方法。

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 isMemberOfClass方法

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、

-(BOOL) respondsToSelector: selector 判读实例是否有这样方法

+(BOOL) instancesRespondToSelector:  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

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

// 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

// 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：

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

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：

2012-07-04 14:57:55.905 ObjectiveCTest[3085:f803] 张三老师 教数学