我可以有条件地禁用仅在第一个响应者响应选择器时启用的NSMenuItem吗？

Question

I have an NSMenuItem that is enabled/disabled based on whether or not the first responder responds to a specific selector.

My problem is that there are conditions in which I do not want the item enabled for the first responder.

But I can't just conditionally remove a method definition during runtime to disable the menu item

For an example of what I mean:
I have a NSDocument -based application, and I have two main subclasses-- an ImageDocument and a VideoDocument

I have an NSMenuItem called "Capture Frame", which turns a frame of a video into an image. But obviously this should be disabled on an ImageDocument , and only enabled on a VideoDocument .

The NSMenuItem is enabled if the first responder responds to -captureFrame

The VideoDocumentController has a method, -captureFrame , so it's enabled. The ImageDocumentController does not, so the menu item is never enabled.

But , there are specific VideoDocument s that I do not want to have that menu item enabled for. What could be the best way for me to disable this menu item in order to handle special cases?

Answer 1

In your VideoDocument class, override the NSDocument method validateUserInterfaceItem: . Alternatively, you can override validateUserInterfaceItem: in a subclass of NSDocumentController . Be sure to call super to keep the built-in functionality of this method. See Apple's docs on UI validation for an example.