判断对象类型1

-(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

使用方法：

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//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");  
}  

//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");  
}

判断对象类型2

-(BOOL) respondsToSelector: selector 判断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

使用方法

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// 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" );  
}  
// 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" );  
}

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。
实例如下：

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Person *person = [[Person alloc] init];  
Teacher *teacher = [[Teacher alloc] init];  
  
id p = person;  
id t = teacher;