Objective-C語法之動態類型(isKindOfClass, isMemberOfClass,id)等

對象在運行時獲取其類型的能力稱為內省。內省可以有多種方法實現。

判斷對象類型

-(BOOL) isKindOfClass: classObj判斷是否是這個類或者這個類的子類的實例

-(BOOL) isMemberOfClass: classObj 判斷是否是這個類的實例

我們試試這兩個方法的使用。

1、新建Person類繼承NSObject,新建Teacher類繼承Person

1.1、新建Person類

1. #import <Foundation/Foundation.h>
3. @interface Person : NSObject
4. {
5. NSString *name;
6. }
7. -(void)setName:(NSString*)n;
9. @end

1. #import "Person.h"
3. @implementation Person
4. -(void)setName:(NSString *)n
5. {
6. name = n;
7. }
9. @end

1.2新建Teacher類

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

1. #import "Teacher.h"
3. @implementation Teacher
4. -(void)teach
5. {
6. NSLog(@"我教數學");
7. }
8. @end

1.3 我們先實驗下isMemberOfClass方法。

1. NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];
2. Person *person = [[Person alloc] init];
3. Teacher *teacher = [[Teacher alloc] init];
5. //YES
6. if ([teacher isMemberOfClass:[Teacher class]]) {
7. NSLog(@"teacher Teacher類的成員");
8. }
9. //NO
10. if ([teacher isMemberOfClass:[Person class]]) {
11. NSLog(@"teacher Person類的成員");
12. }
13. //NO
14. if ([teacher isMemberOfClass:[NSObject class]]) {
15. NSLog(@"teacher NSObject類的成員");
16. }
17. [person release];
18. [teacher release];
19. [pool release];

打印結果：

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

只有第一個判斷打印出來，isMemberOfClass判斷是否是屬於這類的實例，是否跟父類有關系他不管。

1.4 isMemberOfClass方法

1. NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];
2. Person *person = [[Person alloc] init];
3. Teacher *teacher = [[Teacher alloc] init];
5. //YES
6. if ([teacher isKindOfClass:[Teacher class]]) {
7. NSLog(@"teacher 是 Teacher類或Teacher的子類");
8. }
9. //YES
10. if ([teacher isKindOfClass:[Person class]]) {
11. NSLog(@"teacher 是 Person類或Person的子類");
12. }
13. //YES
14. if ([teacher isKindOfClass:[NSObject class]]) {
15. NSLog(@"teacher 是 NSObject類或NSObject的子類");
16. }
17. [person release];
18. [teacher release];
19. [pool release];

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

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

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

三個結果都打印出來了。

2、

-(BOOL) respondsToSelector: selector 判讀實例是否有這樣方法

+(BOOL) instancesRespondToSelector: 判斷類是否有這個方法。此方法是類方法，不能用在類的對象

2.1 respondsToSelector的使用

這裡不寫對象的創建和釋放了，參考上面的代碼

1. // YES
2. if ( [teacher respondsToSelector: @selector( setName: )] == YES ) {
3. NSLog(@"teacher responds to setSize: method" );
4. }
6. // NO
7. if ( [teacher respondsToSelector: @selector( abcde )] == YES ) {
8. NSLog(@"teacher responds to nonExistant method" );
9. }
11. // YES
12. if ( [Teacher respondsToSelector: @selector( alloc )] == YES ) {
13. NSLog(@"teacher class responds to alloc method\n" );
14. }

打印結果：

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

中間的那個判斷我隨便寫了個selector,當然沒有了。respondsToSelector 檢查類方法 alloc返回YES

2.2 instancesRespondToSelector

1. // NO
2. if ( [Person instancesRespondToSelector: @selector(teach)] == YES ) {
3. NSLog(@"Person instance responds to teach method" );
4. }
6. // YES
7. if ( [Teacher instancesRespondToSelector: @selector(teach)] == YES ) {
8. NSLog(@"Teacher instance responds to teach method");
9. }
10. // YES
11. if ( [Teacher instancesRespondToSelector: @selector(setName:)] == YES ) {
12. NSLog(@"Teacher instance responds to setName: method" );
13. }

打印結果：

1. 2012-07-04 14:52:29.378 ObjectiveCTest[2961:f803] Teacher instance responds to teach method
2. 2012-07-04 14:52:29.379 ObjectiveCTest[2961:f803] Teacher instance responds to setName: method

3、Objective-C的id類型

C++ 使用的是強類型：對象必須符合其類型，否則不能通過編譯。在 Objective-C 中，id類型類似於(void*) ,可以指向任何類的實例。而不需要強制轉換。

下面看看使用，

先把Teacher類中的 teach方法修改一下，改成

-(void)teach

{

NSLog(@"%@ 教數學" ,name);

}

然後實現並調用

1. NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];
2. Person *person = [[Person alloc] init];
3. Teacher *teacher = [[Teacher alloc] init];
5. id p = person;
6. id t = teacher;
7. [t setName:@"張三老師"];
8. [t teach];
10. [person release];
11. [teacher release];
12. [pool release];

打印結果：

1. 2012-07-04 14:57:55.905 ObjectiveCTest[3085:f803] 張三老師 教數學