关于在Objective C中命名实例变量

Question

有时我们可以在synthesize语句中明确指定实例变量的名称,例如,

在SomeViewController.h,

//....
@property (nonatomic, retain) NSObject *variable;
//....

在SomeViewController.m,

//....
@synthesize variable = _variable;
//....

但是,如果将实例变量隐式命名为_variable即使我们简单地将它作为:

@synthesize variable;

在SomeViewController.m.

任何人都可以分享为什么有必要吗？谢谢你:D

Answer 1

只是为了避免混淆(见注释):使用= _variable部分@synthesize不是必需的,也不再需要@synthesize它本身.

This effort is only requied, when you want to link the property to a specific instance variable. With earlier Objective-C versions this part of the statement was required to set the name to something different from the property name, so when you want to call the iVar _variable and the property variable. The default would be variable (unlike your question). Without that = something ivar and property have the same name.

BTW, there is nothing wrong with using the same name for both. But having different names, a leading _ would do, makes it more clear to the programmer whether he/she accesses the ivar directly or though the accessor methods. Sometimes this is of vast importance, especially when not using ARC. Therefore it helps avoiding errors.

With current Objective-C, however, you could omit the @synthesize statement at all and go with the defaults in that case. The default automatically synthesized instance variable name would have a leading _ so _variable in your example.