windowDidResignKey

windowDidResignKey is a delegate method in AppKit used by macOS applications to respond when a window loses its status as the key window. The key window is the window that receives keyboard input and is typically the active window for user interaction.

When a window becomes key, it gains the primary focus for keyboard events. A different window or the application becoming inactive can cause the current key window to resign key. The windowDidResignKey method is called on the window’s delegate at that moment, allowing the app to react to the loss of keyboard focus.

This method is part of the NSWindowDelegate protocol and is optional. Developers implement it to perform tasks such as updating the user interface, enabling or disabling controls, or saving transient state when the window relinquishes key status. The notification object provided to the method identifies the window that resigned key status.

In the notification parameter, you can access the affected window with notification.object, which is the NSWindow that resigned key. This can be useful for adjusting app behavior or coordinating with other windows.

Swift example:

func windowDidResignKey(_ notification: Notification) {

if let window = notification.object as? NSWindow {

// Respond to the window losing key status

}

}

Related delegate methods include windowDidBecomeKey and windowWillClose, which handle the opposite event and other window lifecycle changes. See also NSWindowDidResignKeyNotification for the corresponding notification name.