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Posing
Posted on: September 26, 2008 at 12:00 AM

Posing is similar to category but it works a little bit different with the category.

Dynamic Types in Objective-C

Objective-C provides many methods to work with dynamic types. With these methods programmer can check that object is of the given class or not, given method is member of the given class or not etc. Table given below describe some of these methods and their brief description.....

Method	Description
-(BOOL) isKindOfClass: classObj	is object a descendent or member of classObj
-(BOOL) isMemberOfClass: classObj	is object a member of classObj
-(BOOL) respondsToSelector: selector	does the object have a method named specifiec by the selector
+(BOOL) instancesRespondToSelector: selector	does an object created by this class have the ability to respond to the specified selector
-(id) performSelector: selector	invoke the specified selector on the object

^Example: ^{FirstClass.h
FirstClass.m}

#import<Foundation/NSObject.h>
@interface FirstClass:NSObject

-(void)fShow ;
+(void)classShow ;
@end

#import "FirstClass.h"
@implementation FirstClass

   -(void)fShow {
   printf("This is first class.");
   }
   +(void)classShow {
   }

@end

^Second^Class.h^Second^Class.m

#import<Foundation/
     NSObject.h>

@interface SecondClass:
      NSObject

-(void)sShow;
@end

#import "SecondClass.h"

@implementation SecondClass

-(void)sShow {
   printf("This is first
 class.");
   }

@end

^main.m

#import "FirstClass.m"
#import "SecondClass.m"
#import <stdio.h>

int main() {

    FirstClass *fClassObj = [[FirstClass alloc] init];
    SecondClass *sClassObj = [[SecondClass alloc] init];

    /* some methods to work with dynamic types */

    // -(BOOL) isKindOfClass: classObj  ----------- true
     if ( [fClassObj isKindOfClass: [FirstClass class]] == YES ) {
        printf( "fClassObj is kind of FirstClass.\n" );
    }

    // -(BOOL) isKindOfClass: classObj  ----------- false
    if ( [fClassObj isKindOfClass: [SecondClass class]] == YES ) {
        printf( "fClassObj is kind of SecondClass.\n" );
    }
    else
    printf( "fClassObj is not kind of SecondClass.\n" );

    // -(BOOL) isMemberOfClass: classObj ----------- true
     if ( [fClassObj isMemberOfClass: [FirstClass class]] == YES ) {
        printf( "fClassObj is member of FirstClass.\n" );
    }

    // -(BOOL) isMemberOfClass: classObj ----------- false
     if ( [sClassObj isMemberOfClass: [FirstClass class]] == YES ) {
        printf( "sClassObj is member of FirstClass.\n" );
    }
    else
    printf( "sClassObj is not member of FirstClass.\n" );

    // -(BOOL) respondsToSelector: selector ----- true
    if ( [fClassObj respondsToSelector: @selector(fShow)] == YES ) {
        printf( "fClassObj responds to fShow method\n" );
    }

    // -(BOOL) respondsToSelector: selector ----- false
    if ( [sClassObj respondsToSelector: @selector(fShow)] == YES ) {
        printf( "sClassObj responds to fShow method\n" );
    }
    else
       printf( "sClassObj does'nt respond to fShow method\n" );

    // release memory allocated for the objects
    [fClassObj release];
    [sClassObj release];
    return 0;
}

Output:

fClassObj is kind of FirstClass.
fClassObj is not kind of SecondClass.
fClassObj is member of FirstClass.
sClassObj is not member of FirstClass.
fClassObj responds to fShow method
sClassObj does'nt respond to fShow method

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