ios动态添加属性的几种方法

http://blog.csdn.net/shengyumojian/article/details/44919695

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。