macos - How can I detect that the Shift key has been pressed?

Question

I have a NSView subclass and I would like it to react when the user presses the ? Shift key. However, -[NSView keyDown:] (which I currently override) isn't called when modifier keys alone are pressed.

How can I be notified when the Shift key has been pressed?

Answer 1

From the Cocoa event handling guide:

The flagsChanged: method can be useful for detecting the pressing of modifier keys without any other key being pressed simultaneously. For example, if the user presses the Option key by itself, your responder object can detect this in its implementation of flagsChanged:.

More details can be found here.

The documentation for NSResponder also states the following:

flagsChanged:

Informs the receiver that the user has pressed or released a modifier key (Shift, Control, and so on).

-- (void)flagsChanged:(NSEvent *)theEvent