iOS Xcode 4 属性访问
我最近切换到 Xcode 4，但我不太理解这种编写访问器的新方法。 例如，在创建新项目时自动生成的应用程序委托类中，window对象没有在@interface中声明，而是这样
@property (nonatomic, retain) IBOutlet UIWindow *window;
：在实现文件中，我们有@synthesize window=_window;。 在函数中，我们有 self.window 或 _window。
例如：
[self.window makeKeyAndVisible]; // in didFinishLaunchingWithOptions function
[_window release]; // in dealloc function
你能解释一下其中的区别吗？为什么@interface中没有任何内容，为什么我们使用@synthesize window=_window;而不是@synthesize window ; 以及 self.window 和 _window 之间有什么区别，我的意思是我什么时候必须多调用一个而不是另一个？
我有点迷失了，感觉就像我所做的新代码试图做同样的事情但无法正常工作......
谢谢！
I switched to Xcode 4 recently and I don't really understand this new way to write accessors.
For example, in the application delegate class that is auto-generated when creating a new project, the window object is not declared in the @interface but just this way:
@property (nonatomic, retain) IBOutlet UIWindow *window;
Then, in the implementation file, we have the @synthesize window=_window;.
And in the functions, we have either self.window OR _window.
For example:
[self.window makeKeyAndVisible]; // in didFinishLaunchingWithOptions function
[_window release]; // in dealloc function
Can you explain me the difference, why there is nothing in the @interface, why we do @synthesize window=_window; instead of @synthesize window; and what is the difference between self.window and _window, I mean when do I have to call one more than the other?
I'm a bit lost, and feel like the new code I doing trying to do the same in not working properly...
Thanks!
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“为什么
@interface中没有任何内容”运行时正在为您合成 ivar。
“我们为什么要这样做
@synthesize window=_window;这意味着
window属性将使用名为_window的ivar（默认情况下ivar名称是属性的名称）“
self.window和_window之间有什么区别？”前者使用
window“getter”方法（即foo = [self window]），后者直接访问ivar。“为什么我必须多调用一个而不是另一个？”
通常认为在
dealloc方法中使用访问器方法是不安全的，这意味着首选使用 ivar。"Why is there nothing in the
@interface"The runtime is synthesizing the ivar for you.
"Why do we do
@synthesize window=_window;This means that the
windowproperty will use an ivar named_window(by default the ivar name is the name of the property)"What is the difference between
self.windowand_window?"The former is using the
window"getter" method (ie,foo = [self window]), and the latter is accessing the ivar directly."Why do I have to call one more than the other?"
It is generally considered unsafe to use accessor methods in your
deallocmethod, which means using the ivar is preferred.这与 Xcode 4 无关。这是 Objective-C 2.0（Xcode 4 在创建项目模板时默认使用它）。
我建议阅读 The Objective 中有关属性的章节-C 编程语言，这应该使事情变得更加清晰
并且“旧方式”做事仍然有效。您不必在一夜之间更改所有内容，如果您不喜欢自动创建的代码，只需删除它即可，直到您对新语法感到满意为止。
This has nothing to do with Xcode 4. This is Objective-C 2.0 (which Xcode 4 uses by default when creating project templates).
I recommend reading the chapter on properties in The Objective-C Programming Language, that should make things much clearer
And doing things "the old way" will still work. You don't have to change everything overnight, simply remove the auto-created code if you don't like it, until you feel comfortable with the new syntax.