objective-c - 为什么有些对象在objective-c中使用前不需要初始化？

Question

为什么有些对象在objective-c中使用前不需要初始化？例如，为什么这是NSDate *today = [NSDate date];合法的？

Answer 1

它们在date方法中被初始化。这是在 Objective-C 中创建自动释放对象的常用方法。这种形式的分配器称为便利分配器。

要了解更多信息，请阅读 Apple 的 Cocoa 核心能力文档中关于对象创建的“工厂方法”段落：http: //developer.apple.com/library/mac/#documentation/General/Conceptual/DevPedia-CocoaCore/ObjectCreation。 html

要为您自己的类创建便利分配器，请实现一个以您的类命名的类方法（不带前缀）。例如：

@implementation MYThing
...

+ (id)thing
{
  return [[[MYThing alloc] init] autorelease];
}

...
@end

Answer 2

today 在静态日期调用中初始化（并自动释放）。

Answer 3

Answer 4

Two parts.

First, as others have mentioned, a method can initialise and then autorelease an object before returning it. That's part of what's happening here.

The other part is how it's defined. Note how most Objective C definitions begin with a -? The one you mention does not. The signature looks like this:

+ (NSDate*) date;

That is, it's a class method and applies to the class as a whole rather than to an instance of that class.