合成属性和带下划线前缀的变量：这是什么意思？ [英] Synthesized property and variable with underscore prefix: what does this mean?

问题描述

可能重复：

属性名称上的下划线前缀？

？ @synthesize window = _window; 我知道一般来说，它意味着一些类有一个窗口，但为什么使用 _window 而不是窗口？这是一个命名空间的东西吗？

解决方案

在其他语言中使用前面的 m ， m_ 或 _ 来区分它们与本地声明的变量，并表示如果必要，它们应该有写入的访问器（无 classInstance .m_Variable = 5 ）。

如果Objective-C程序员声明ivars遵循这个约定（并且它们应该）并使用基本语法 @synthesize _window; 然后属性的用法变得有点丑陋： classInstance._window = myWindow 或 [classInstance set_window：myWindow] 。使用语法 @synthesize window = _window; 允许Obj-C程序员使用流行的编程标准（前面的ivars与 _ ），同时具有使用Apple标准的属性访问器 classInstance.window = myWindow 和 [classInstance setWindow：myWindow] 。

Possible Duplicate:
Underscore prefix on property name?

What does this mean? @synthesize window=_window; I know that in general it means that 'some class' has a window, but why use _window instead of just window? Is this a namespace thing?

解决方案

I'll give a go at describing this programming convention in basic English.

It is a very common convention in other languages to name member variables with a preceding m, m_, or _ to distinguish them from locally declared variables and to signify that they should have accessors written, if necessary (no classInstance.m_Variable = 5).

If an Objective-C programmer declares ivars following this convention (and they should) and uses the basic syntax @synthesize _window; then the usage for the property becomes somewhat ugly: classInstance._window = myWindow or [classInstance set_window:myWindow]. Using the syntax @synthesize window=_window; allows the Obj-C programmer to utilize a popular programming standard (preceding ivars with _) while simultaneously having property accessors that use the Apple standard classInstance.window = myWindow and [classInstance setWindow:myWindow].

这篇关于合成属性和带下划线前缀的变量：这是什么意思？的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！