ios 怎么动态向已有类添加属性

在ios运行过孙猜程中，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和档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的指定唤凯乱属性值

+ (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。

java无法动态添加方法和属性。

java是一门编译性的语言，常见脚本语言是野空解析性语言。

编译性语言的类的族兄成员与属性在代码编译完成后就兆脊袭已经固定了，无法动态添加；

解释性语言是在运行时可以动态为对象添加属性和方法。

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