iOS:将 self 和下划线(_)与变量一起使用 [英] iOS: Usage of self and underscore(_) with variable

问题描述

可能的重复:
cocoa Objective-c 类中变量前面的下划线是如何工作的?

在合成如下后，我对使用 self 或下划线和变量名感到非常困惑:

I have been very confused with using self or underscore with variable name after synthesizing it like below:

In .h file:
@property(nonatomic, strong) NSMutableArray *users;

In .m file:
@synthesize users = _users;

根据我在使用 self.users 时的理解，OS 会确保在 set 方法中释放先前分配的内存，因此我们不需要明确注意.

Based on my understandings when I use self.users, OS will make sure to release previously allocated memory in set method so we don't need to take care explicitly.

_users 是用户的实例变量，通常在访问用户变量时使用.如果我使用 _users 来改变它的值，那么它不会触发 KVO 委托，它不会通知观察用户值变化的类.

_users is an instance variable for users and should be normally used while accessing the users variable. If I use _users to change its value then it won't fire KVO delegate which will not notify a class observing users value change.

此外，self.users 允许在方法名称中区分虚拟变量，如下所示，

Moreover, self.users allows differentiating dummy variable in the method name like below,

- (void)assignUsers:(NSMutableArray*)users {
      self.users = users;
}

有人可以告诉我在使用 _users 或 self.users 时是否有任何我理解错误或遗漏的地方吗?

Could someone please tell me if there is anything that I understood wrong or missing while using _users or self.users?

推荐答案

我认为考虑编译器如何(或可能)实现属性会有所帮助.

I think it helps to consider how properties are (or might be) implemented by the compiler.

当您编写 self.users = array; 时，编译器会将其转换为 [self setUsers:array];当您编写 array = self.users; 时，编译器会将其转换为 array = [self users];

When you write self.users = array; the compiler translates this to [self setUsers:array]; When you write array = self.users; the compiler translates this to array = [self users];

@synthesize 向您的对象添加一个 ivar(除非您自己添加)，并实现了 -users 和 -setUsers: 为您提供的访问器方法(除非您提供自己的)

@synthesize adds an ivar to your object (unless you added it yourself), and implements the -users and -setUsers: accessor methods for you (unless you provide your own)

如果您使用 ARC，-setUsers: 将类似于:

If you're using ARC, -setUsers: will look something like:

- (void)setUsers:(NSArray *)users
{
    _users = users; // ARC takes care of retaining and release the _users ivar
}

如果您使用的是 MRC(即未启用 ARC)，-setUsers: 将类似于*:

If you're using MRC (i.e. ARC is not enabled), -setUsers: will look something like*:

- (void)setUsers:(NSArray *)users
{
    [users retain];
    [_users release];
    _users = users;
}

* - 请注意，这是 -setUsers 的简化非原子实现:

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