在ios运行过程中，有几种方式能够动态的添加属性。
1-通过runtime动态关联对象
主要用到了objc_setAssociatedObject，objc_getAssociatedObject以及objc_removeAssociatedObjects
//在目标target上添加关联对象，属性名propertyname(也能用来添加block)，值value+ (void)addAssociatedWithtarget:(id)target withPropertyName:(NSString *)propertyName withValue:(id)value { id property = objc_getAssociatedObject(target, &propertyName); if(property == nil) { property = value; objc_setAssociatedObject(target, &propertyName, property, OBJC_ASSOCIATION_RETAIN); }}//获取目标target的指定关联对象值+ (id)getAssociatedValueWithTarget:(id)target withPropertyName:(NSString *)propertyName { id property = objc_getAssociatedObject(target, &propertyName); return property;}
优点：这种方式能够使我们快速的在一个已有的class内部添加一个动态属性或block块。
缺点：不能像遍历属性一样的遍历我们所有关联对象，且不能移除制定的关联对象，只能通过removeAssociatedObjects方法移除所有关联对象。
2-通过runtime动态添加Ivar
主要用到objc_allocateClassPair，class_addIvar，objc_registerClassPair
//在目标target上添加属性(已经存在的类不支持，可跳进去看注释)，属性名propertyname，值value+ (void)addIvarWithtarget:(id)target withPropertyName:(NSString *)propertyName withValue:(id)value { if (class_addIvar([target class], [propertyName UTF8String], sizeof(id), log2(sizeof(id)), "@")) { YYLog(@"创建属性Ivar成功"); }}//获取目标target的指定属性值+ (id)getIvarValueWithTarget:(id)target withPropertyName:(NSString *)propertyName { Ivar ivar = class_getInstanceVariable([target class], [propertyName UTF8String]); if (ivar) { id value = object_getIvar(target, ivar); return value; } else { return nil; }}
优点：动态添加Ivar我们能够通过遍历Ivar得到我们所添加的属性。
缺点：不能在已存在的class中添加Ivar，所有说必须通过objc_allocateClassPair动态创建一个class，才能调用class_addIvar创建Ivar，最后通过objc_registerClassPair注册class。
3-通过runtime动态添加property
主要用到class_addProperty，class_addMethod，class_replaceProperty，class_getInstanceVariable
//在目标target上添加属性，属性名propertyname，值value+ (void)addPropertyWithtarget:(id)target withPropertyName:(NSString *)propertyName withValue:(id)value { //先判断有没有这个属性，没有就添加，有就直接赋值 Ivar ivar = class_getInstanceVariable([target class], [[NSString stringWithFormat:@"_%@", propertyName] UTF8String]); if (ivar) { return; } /* objc_property_attribute_t type = { "T", "@/"NSString/"" }; objc_property_attribute_t ownership = { "C", "" }; // C = copy objc_property_attribute_t backingivar = { "V", "_privateName" }; objc_property_attribute_t attrs[] = { type, ownership, backingivar }; class_addProperty([SomeClass class], "name", attrs, 3); */ //objc_property_attribute_t所代表的意思可以调用getPropertyNameList打印，大概就能猜出 objc_property_attribute_t type = { "T", [[NSString stringWithFormat:@"@/"%@/"",NSStringFromClass([value class])] UTF8String] }; objc_property_attribute_t ownership = { "&", "N" }; objc_property_attribute_t backingivar = { "V", [[NSString stringWithFormat:@"_%@", propertyName] UTF8String] }; objc_property_attribute_t attrs[] = { type, ownership, backingivar }; if (class_addProperty([target class], [propertyName UTF8String], attrs, 3)) { //添加get和set方法 class_addMethod([target class], NSSelectorFromString(propertyName), (IMP)getter, "@@:"); class_addMethod([target class], NSSelectorFromString([NSString stringWithFormat:@"set%@:",[propertyName capitalizedString]]), (IMP)setter, "v@:@"); //赋值 [target setValue:value forKey:propertyName]; NSLog(@"%@", [target valueForKey:propertyName]); YYLog(@"创建属性Property成功"); } else { class_replaceProperty([target class], [propertyName UTF8String], attrs, 3); //添加get和set方法 class_addMethod([target class], NSSelectorFromString(propertyName), (IMP)getter, "@@:"); class_addMethod([target class], NSSelectorFromString([NSString stringWithFormat:@"set%@:",[propertyName capitalizedString]]), (IMP)setter, "v@:@"); //赋值 [target setValue:value forKey:propertyName]; }}id getter(id self1, SEL _cmd1) { NSString *key = NSStringFromSelector(_cmd1); Ivar ivar = class_getInstanceVariable([self1 class], "_dictCustomerProperty"); //basicsViewController里面有个_dictCustomerProperty属性 NSMutableDictionary *dictCustomerProperty = object_getIvar(self1, ivar); return [dictCustomerProperty objectForKey:key];}void setter(id self1, SEL _cmd1, id newValue) { //移除set NSString *key = [NSStringFromSelector(_cmd1) stringByReplacingCharactersInRange:NSMakeRange(0, 3) withString:@""]; //首字母小写 NSString *head = [key substringWithRange:NSMakeRange(0, 1)]; head = [head lowercaseString]; key = [key stringByReplacingCharactersInRange:NSMakeRange(0, 1) withString:head]; //移除后缀 ":" key = [key stringByReplacingCharactersInRange:NSMakeRange(key.length - 1, 1) withString:@""]; Ivar ivar = class_getInstanceVariable([self1 class], "_dictCustomerProperty"); //basicsViewController里面有个_dictCustomerProperty属性 NSMutableDictionary *dictCustomerProperty = object_getIvar(self1, ivar); if (!dictCustomerProperty) { dictCustomerProperty = [NSMutableDictionary dictionary]; object_setIvar(self1, ivar, dictCustomerProperty); } [dictCustomerProperty setObject:newValue forKey:key];}+ (id)getPropertyValueWithTarget:(id)target withPropertyName:(NSString *)propertyName { //先判断有没有这个属性，没有就添加，有就直接赋值 Ivar ivar = class_getInstanceVariable([target class], [[NSString stringWithFormat:@"_%@", propertyName] UTF8String]); if (ivar) { return object_getIvar(target, ivar); } ivar = class_getInstanceVariable([target class], "_dictCustomerProperty"); //basicsViewController里面有个_dictCustomerProperty属性 NSMutableDictionary *dict = object_getIvar(target, ivar); if (dict && [dict objectForKey:propertyName]) { return [dict objectForKey:propertyName]; } else { return nil; }}
优点：这种方法能够在已有的类中添加property，且能够遍历到动态添加的属性。
缺点：比较麻烦，getter和setter需要自己写，且值也需要自己存储，如上面的代码，我是把setter中的值存储到了_dictCustomerProperty里面，在getter中再从_dictCustomerProperty读出值。
4-通过setValue:forUndefinedKey动态添加键值
这种方法优点类似property，需要重写setValue:forUndefinedKey和valueForUndefinedKey:，存值方式也一样，需要借助一个其它对象。由于这种方式没通过runtime，所以也比较容易理解。在此就不举例了。
