访问实例变量的语法? (目标C) [英] Syntax for accessing instance variables? (Objective-C)

问题描述

在Objective-C中访问实例变量的正确语法是什么?

What is the proper syntax for accessing an instance variable in Objective-C?

假设我们有这个变量:

@interface thisInterface : UIViewController {
    NSMutableString *aString;
}

@property (nonatomic, retain) NSMutableString *aString;

它是合成的.

当我们要访问它时，我们首先要分配和初始化它.在Objective-C中编程大约一个月以来，我已经看到了两种不同形式的语法.我见过人们只是简单地aString = [[NSMutableString alloc] initWithString:@"hi"]，他们在其中分配字符串.我还看到人们以self.aString开始它，然后他们继续初始化他们的ivar.我想我只是想找出初始化实例变量的最正确方法是什么，因为在前面的示例中，我从中收到了EXC_BAD_ACCESS错误.在添加self.之后，它没有出现.

When we want to access it, we first would want to allocate and initialize it. Having programmed in Objective-C for about a month now, I've seen two different forms of syntax. I've seen people do simply aString = [[NSMutableString alloc] initWithString:@"hi"], where they allocate the string like that; I've also seen people start it off with self.aString and then they proceed to initialize their ivar. I guess I'm just trying to figure out what is the most proper way of initializing an instance variable, because with the former example, I have received EXC_BAD_ACCESS errors from it. After prepending the self. though, it didn't appear.

如果这是一个重复的问题，请原谅我，但是在阅读了有关SO的一些帖子后，这使我感到好奇.我正在尝试使用Objective-C学习正确的语法，因为我更喜欢正确而不是草率.

Forgive me if this is a duplicate question, but after reading some posts on SO, it's made me curious. I'm trying to learn the proper syntax with Objective-C because I prefer being proper rather than sloppy.

推荐答案

如果您声明了一个属性，并在.m文件中@synthesize对其进行了设置，则只需这样设置即可:

If you have declared a property and @synthesize it in the .m file, you simply set it like this:

self.aString = @"hi"; // or [[NSMutableString alloc] initWithString:@"hi"];

使用self.varName可以利用属性声明的实际作用-它可以处理新值的保留(因为属性具有retain属性)，为您释放旧值等.

Using self.varName takes advantage of what your property declaration actually does- it handles retention of the new value (since your property has the retain attribute), releasing the old value, etc for you.

如果您只是这样做:

aString = someValue;

...您可能正在泄漏aString中的原始值，因为不使用self.aString您是直接通过属性访问变量.

... you may be leaking the original value that was in aString, since without using self.aString you are accessing the variable directly vs through the property.

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