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
[cpp]
#import <Foundation/Foundation.h>
@interface Person : NSObject
{
NSString *name;
}
-(void)setName:(NSString*)n;
@end
[cpp]
#import "Person.h"
@implementation Person
-(void)setName:(NSString *)n
{
name = n;
}
@end
1.2新建Teacher類
[cpp]
#import "Person.h"
@interface Teacher : Person
-(void)teach;
@end
[cpp]
#import "Teacher.h"
@implementation Teacher
-(void)teach
{
NSLog(@"我教數學");
}
@end
1.3 我們先實驗下isMemberOfClass方法。
[cpp]
NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];
Person *person = [[Person alloc] init];
Teacher *teacher = [[Teacher alloc] init];
//YES
if ([teacher isMemberOfClass:[Teacher class]]) {
NSLog(@"teacher Teacher類的成員");
}
//NO
if ([teacher isMemberOfClass:[Person class]]) {
NSLog(@"teacher Person類的成員");
}
//NO
if ([teacher isMemberOfClass:[NSObject class]]) {
NSLog(@"teacher NSObject類的成員");
}
[person release];
[teacher release];
[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
[cpp]
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類或Teacher的子類");
}
//YES
if ([teacher isKindOfClass:[Person class]]) {
NSLog(@"teacher 是 Person類或Person的子類");
}
//YES
if ([teacher isKindOfClass:[NSObject class]]) {
NSLog(@"teacher 是 NSObject類或NSObject的子類");
}
[person release];
[teacher release];
[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
[cpp]
// 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
[cpp]
// 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" );
}
打印結果：
[cpp]
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
[cpp]
NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];
Person *person = [[Person alloc] init];
Teacher *teacher = [[Teacher alloc] init];
id p = person;
id t = teacher;
[t setName:@"張三老師"];
[t teach];
[person release];
[teacher release];
[pool release];
打印結果：
[cpp] view plaincopy
2012-07-04 14:57:55.905 ObjectiveCTest[3085:f803] 張三老師 教數學
