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
ps：本篇新建的類主要用于熟悉本篇內容設計，未考慮內存管理因素。
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
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#import?
@interface?Person?:?NSObject
{
NSString?*name;
}
-(void)setName:(NSString*)n;
@end
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#import?"Person.h"
@implementation?Person
-(void)setName:(NSString?*)n
{
name?=?n;
}
@end
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#import?"Person.h"
@interface?Teacher?:?Person
-(void)teach;
@end
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#import?"Teacher.h"
@implementation?Teacher
-(void)teach
{
NSLog(@"我教數學");
}
@end
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NSAutoreleasePool?*pool?=?[[NSAutoreleasePool?alloc]?init];
Person?*person?=?[[Person?alloc]?init];
Teacher?*teacher?=?[[Teacher?alloc]?init];
//YES
if([teacher?isMemberOfClass:[Teacherclass]])?{
NSLog(@"teacher?Teacher類的成員");
}
//NO
if([teacher?isMemberOfClass:[Personclass]])?{
NSLog(@"teacher?Person類的成員");
}
//NO
if([teacher?isMemberOfClass:[NSObjectclass]])?{
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判斷是否是屬于這類的實例，是否跟父類有關系他不管。
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NSAutoreleasePool?*pool?=?[[NSAutoreleasePool?alloc]?init];
Person?*person?=?[[Person?alloc]?init];
Teacher?*teacher?=?[[Teacher?alloc]?init];
//YES
if([teacher?isKindOfClass:[Teacherclass]])?{
NSLog(@"teacher?是?Teacher類或Teacher的子類");
}
//YES
if([teacher?isKindOfClass:[Personclass]])?{
NSLog(@"teacher?是?Person類或Person的子類");
}
//YES
if([teacher?isKindOfClass:[NSObjectclass]])?{
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。
-(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
這里不寫對象的創建和釋放了，參考上面的代碼
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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");
}
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
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//?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：
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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
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類型類似于(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);
}
然后實現并調用
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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：
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2012-07-04?14:57:55.905?ObjectiveCTest[3085:f803]?張三老師?教數學
