NSFontManager is a crucial class in the macOS development environment, part of the AppKit framework. It provides a centralized way to manage and select fonts within macOS applications. This utility is essential for developers who need to offer users the ability to customize text appearance within their applications. By understanding how to use NSFontManager, developers can enhance the user experience by enabling font selection and modification features.

Examples:

1. Creating an NSFontManager Instance: To use NSFontManager, you first need to create an instance. Typically, you don't need to instantiate it directly as it provides a shared instance.

   import Cocoa
   
   let fontManager = NSFontManager.shared

2. Using NSFontManager to Select Fonts: You can allow users to select fonts using the standard font panel provided by NSFontManager. This is usually done in response to a user action, such as clicking a button.

   @IBAction func showFontPanel(_ sender: Any) {
      let fontManager = NSFontManager.shared
      fontManager.orderFrontFontPanel(self)
   }

3. Applying Selected Fonts to Text: When a user selects a font, you can retrieve the selected font and apply it to a text view or any other text-containing component.

   func changeFont(_ sender: NSFontManager?) {
      guard let fontManager = sender else { return }
      if let selectedFont = fontManager.selectedFont {
          // Assuming textView is an instance of NSTextView
          textView.font = selectedFont
      }
   }

4. Responding to Font Changes: To respond to font changes, you need to implement the changeFont method and ensure your object is the target of the NSFontManager.

   override func changeFont(_ sender: Any?) {
      guard let fontManager = sender as? NSFontManager else { return }
      let newFont = fontManager.convert(textView.font!)
      textView.font = newFont
   }

5. Customizing the Font Panel: You can customize the font panel to restrict the types of fonts available or to add custom options.

   func customizeFontPanel() {
      let fontManager = NSFontManager.shared
      let fontPanel = fontManager.fontPanel(true)
      // Customize the font panel as needed
   }