cocoa - NSObject Controller 的选择是什么？

Question

在 Xcode 6.2 中，在绑定(bind)检查器中我看到:

谁能解释一下将 Controller 键设置为选择意味着什么？苹果文档说:

selection:
Returns a proxy object representing the [NSObjectController's] selection.

一点帮助都没有。

Answer 1

我已经拼凑出了部分谜题。来自 Apple Developer docs :

Controllers require content to manipulate and there are a number of options for setting this content. It can be done ... through bindings...
...
NSObjectController and its subclasses are initialized with the method initWithContent:, passing a content object or nil if you intend to use the content bindings. You can explicitly set the content of an existing controller using the setContent: method. It is far more common to provide content for controllers by establishing a binding to one of their exposed Controller Content bindings.

NSObjectController exposes a single binding for content called contentObject. You can establish a binding from contentObject to any object that is key-value-coding and key-value-observing compliant for the keys that you intend to have the controller operate on.

来自 SO post :

For an NSObjectController, the selection is the content object.

显然，NSObjectController 的选择@property 被分配了contentObject，这使您能够进行绑定(bind)。

更多 generally :

NSObjectController and its subclasses ... support tracking of the currently selected object or objects

我认为当前选择的对象必须表示在 View 中选择的控件。

There are two methods that are commonly used to access the objects that are currently selected: selection and selectedObjects.

我认为对于 NSObjectController，View 中选择的控件是没有意义的，因此 NSObjectController 的选择 @property 被分配给了 contentObject。