目标C：如果@property似乎自动执行，为什么要在.h成员区域中声明ivars？ [英] Objective C: Why do we declare ivars in the .h member area if @property seems to do it automatically?

问题描述

在实现界面时，教程和文献中常见的方法是声明一个ivar，然后设置 @property 然后 @synthesize 。

In implementing an interface it seems the common method in tutorials and literature is to declare an ivar and then set the @property then @synthesize.

@interface MyClass : NSObject {
NSString *myString;
}

@property (nonatomic, retain) NSString *myString;
@end

但是，省略明确的声明，只是放置@property具有相同的效果。

However, omitting the explicit declaration and just putting @property has the same effect.

@interface MyClass: NSObject {
}

@property (nonatomic, retain) NSString *myString;
@end

所以大多数人如何使用 @property 和明确的声明？不好吗？

So how come most people use @property and an explicit declaration? Is it bad form not to?

推荐答案

以前是必要的。 Objective-C运行时有两个不同版本：仅32位的旧运行时（旧版）和32位/ 64位运行时（新的32位运行时仅在iOS设备上使用， iOS模拟器）。

It used to be necessary. There are two different versions of the Objective-C runtime: a 32-bit-only "legacy" runtime (the old one) and a 32/64-bit runtime (the new 32-bit runtime is only used on iOS devices and for the iOS simulator).

我认为唯一需要的地方是当您以32位模式（10.5或10.6）运行应用程序时。其他地方（64位Leopard，64位Snow Leopard，Lion，iOS）使用了具有自动ivar综合的较新的运行时，并将所产生的ivars称为合成ivars。

I think the only place this is still necessary is when you're running the app in 32-bit mode (either 10.5 or 10.6). Everywhere else (64-bit Leopard, 64-bit Snow Leopard, Lion, iOS) uses the newer runtime that has "automatic ivar synthesis", and the resulting ivars are referred to as "synthesized ivars".

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