windowDidBecomeMain

windowDidBecomeMain is an optional delegate method of NSWindowDelegate in AppKit. It is called when a window becomes the main window of its application. The main window is the window that represents the app’s primary active document or focus for actions, and it is distinct from the key window, which is the one that receives keyboard input.

The method receives a notification object; the window that became main is available from notification.object. Implementing this method lets a window’s delegate respond to the change in active window, such as updating user interface elements, enabling or disabling controls, or adjusting state to reflect the newly active document.

Relationship to other window lifecycle events: the main window concept differs from the key window. A window can be key without being main, though in many apps the main and key windows coincide. Other related delegate methods include windowDidBecomeKey: and windowDidResignMain:, which track changes to the key window and main window respectively, and the NSWindowDidBecomeMainNotification notification.

Example usage:

Objective-C

- (void)windowDidBecomeMain:(NSNotification *)notification {

NSWindow *win = notification.object;

// Update UI or application state for the new main window

}

Swift

func windowDidBecomeMain(_ notification: Notification) {

if let window = notification.object as? NSWindow {

// Update UI or application state for the new main window

}

}

Notes: Implementing windowDidBecomeMain is optional; developers typically use it to synchronize UI with the active window or document.