(转)Objective-C语法之动态类型(isKindOfClass, isMemberOfClass,id)等
本文转自http://blog.csdn.net/totogo2010/article/details/7714960
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
ps:本篇新建的类主要用于熟悉本篇内容设计,未考虑内存管理因素。
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 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、
-(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
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