iOS：使用self和下划线（_）和变量 [英] iOS: Usage of self and underscore(_) with variable

问题描述

可能重复：

我在使用自变量或带有变量名的下划线后非常困惑，如下所示： / p>

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;

根据我使用self.users时的理解，操作系统会确保释放以前分配的内存set方法所以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users变量时使用。如果我使用_users更改它的值，那么它将不会触发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 it's value then it won't fire KVO delegate which will not notify a class observing users value change.

此外，self.users允许区分虚拟方法名称中的变量如下所示，

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

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

有人可以告诉我是否有任何我理解错误或丢失的事情使用_users或self.users。谢谢。

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

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，编译器将其转换为 [self setUsers：array] ;
当您编写 array = self.users; 时，编译器将其转换为 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 为对象添加一个ivar（除非除外你自己添加），并为你实现 -users 和 -setUsers：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
}

如果你是使用 MRC （即 ARC 未启用）， -setUsers：将类似*：

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，这是一个简化的非原子实现 -setUsers：

* - Note that this is a simplified, nonatomic implementation of -setUsers:

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