1>.methods1
直接在category的.h中添加，这时xcode会有warning。
Property 'test1' requires method 'test1' to be defined - use @dynamic or provide a method implementation in this category
按照提示在.m文件在@dynamic关键字修改就OK了。dynamic在编译时不会检查setter/getter的实现，在运行时setter/getter会动态绑定，在需要setter/getter的class中自己实现就OK了。
#import <Foundation/Foundation.h>
@interface NSObject (AddProperty1)
@property(nonatomic,strong)NSString *test1;
@end
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#import "NSObject+AddProperty1.h"
@implementation NSObject (AddProperty1)
@dynamic test1;
@end
(在用这种方法添加proprety，使用setter/getter的class如果不implementation会crash的)
2>.methods2
//只用在.h文件添加协议
#import <Foundation/Foundation.h>
@protocol NSObjectProtocol <NSObject>
@optional
@property(nonatomic,strong)NSString *test3;
@end
@interface NSObject (AddProperty3)<NSObjectProtocol>
@end
同上一种方法一样，在使用setter/getter的class中要implementation，否则会crash
3>.methods3
#import <Foundation/Foundation.h>
@interface NSObject (AddProperty2)
@property(nonatomic,strong)NSString *test2;
@end
----------------------------------------------------------------------
#import "NSObject+AddProperty2.h"
#import <objc/runtime.h>
@implementation NSObject (AddProperty2)
-(NSString*)test2{
return objc_getAssociatedObject(self, @selector(test2));
}
-(void)setTest2:(NSString *)test2{
objc_setAssociatedObject(self, @selector(test2), test2, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
}
@end
利用objctive-c的runtime特性。个人更偏好于第三种方法，改动最小，而且在不知道源码的源码的情况下也能add property
附上Demo省得以后自己忘记了
参考：https://www.cnblogs.com/starer/p/3813674.html
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VKOOY
