几个基本方法的说明

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-(BOOL) isKindOfClass:class-object

对象是否为class-object或其子类的成员

-(BOOL) isMemberOfClass:class-object

对象是否为class-object

+(BOOL) isSubclassOfClass:class-object

类是指定类的子类吗？

-(BOOL) respondsToSeletor.selector

对象是否能响应selector方法

+(BOOL) linstancesRespondRespondToSelector:selector

类是否能响应selector方法

-(id) performSelector:selector

应用selector指定的方法

-(id) performSelector:selector withobject:object

应用selector指定的方法传递参数object

class-object

根据类名或一个对象生成一个class-object，可以发送class消息

[Square class];//通过类名声明

[mySquare class];//通过对象名声明

判定两个对象是否在一个类

if([obj1 class] == [obj2 class])

@selector指令：

为某个方法生成一个SEL值

@selector(alloc)

@selector(setTo:over:)

[Square instancesRespondToSelector:@selecor(setSide)];

-(id)PerformSelector:selector

-(BOOL) respondsToSeletor:selector

                          SEL action = @selector (draw);
                         id graphicObject = myFraction;
                         if([graphicObject respondsToSelector:action] == YES)
                             [graphicObject performSelector:action]
                         else
                             //error handling code here