Cocoa Objective-c 类中变量前面的下划线如何工作? [英] How does an underscore in front of a variable in a cocoa objective-c class work?

问题描述

我在一些 iPhone 示例中看到，属性在变量前使用了下划线 _.有谁知道这是什么意思?或者它是如何工作的?

I've seen in a few iPhone examples that attributes have used an underscore _ in front of the variable. Does anyone know what this means? Or how it works?

我使用的接口文件如下所示:

An interface file I'm using looks like:

@interface MissionCell : UITableViewCell {
    Mission *_mission;
    UILabel *_missionName;
}

@property (nonatomic, retain) UILabel *missionName;

- (Mission *)mission;

我不确定上面具体做了什么，但是当我尝试将任务名称设置为:

I'm not sure exactly what the above does but when I try to set the mission name like:

aMission.missionName = missionName;

我收到错误:

在非结构或联合体中请求成员missionName"

request for member 'missionName' in something not a structure or union

推荐答案

如果你为你的 ivars 使用下划线前缀(这只不过是一个常见的约定，但很有用)，那么你需要做 1 件额外的事情所以自动生成的访问器(用于属性)知道要使用哪个 ivar.具体来说，在您的实现文件中，您的 synthesize 应如下所示:

If you use the underscore prefix for your ivars (which is nothing more than a common convention, but a useful one), then you need to do 1 extra thing so the auto-generated accessor (for the property) knows which ivar to use. Specifically, in your implementation file, your synthesize should look like this:

@synthesize missionName = _missionName;

更一般地说，这是:

@synthesize propertyName = _ivarName;

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