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
#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;
}
@end1.2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");
}
@end1.3 我们先实验下isMemberOfClass方法。
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
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
// 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
