Restore active preference when reopening window

Sources/Preferences/PreferencesStyleController.swift

@@ -11,6 +11,6 @@ protocol PreferencesStyleController: AnyObject {
 }
 
 protocol PreferencesStyleControllerDelegate: AnyObject {
-	func activateTab(preferenceIdentifier: PreferencePaneIdentifier?, animated: Bool)
+	func activateTab(preferenceIdentifier: PreferencePaneIdentifier, animated: Bool)
 	func activateTab(index: Int, animated: Bool)
 }

Sources/Preferences/PreferencesTabViewController.swift

@@ -1,7 +1,7 @@
 import Cocoa
 
 final class PreferencesTabViewController: NSViewController, PreferencesStyleControllerDelegate {
-	private var activeTab: Int!
+	private var activeTab: Int?
 	private var preferencePanes = [PreferencePane]()
 	internal var preferencePanesCount: Int {
 		return preferencePanes.count
@@ -54,19 +54,12 @@ final class PreferencesTabViewController: NSViewController, PreferencesStyleCont
 		window.toolbar = toolbar
 	}
 
-	func activateTab(preferencePane: PreferencePane?, animated: Bool) {
-		guard let preference = preferencePane else {
-			return activateTab(index: 0, animated: animated)
-		}
-
-		activateTab(preferenceIdentifier: preference.preferencePaneIdentifier, animated: animated)
+	func activateTab(preferencePane: PreferencePane, animated: Bool) {
+		activateTab(preferenceIdentifier: preferencePane.preferencePaneIdentifier, animated: animated)
 	}
 
-	func activateTab(preferenceIdentifier: PreferencePaneIdentifier?, animated: Bool) {
-		guard
-			let preferenceIdentifier = preferenceIdentifier,
-			let index = (preferencePanes.firstIndex { $0.preferencePaneIdentifier == preferenceIdentifier })
-		else {
+	func activateTab(preferenceIdentifier: PreferencePaneIdentifier, animated: Bool) {
+		guard let index = (preferencePanes.firstIndex { $0.preferencePaneIdentifier == preferenceIdentifier }) else {
 			return activateTab(index: 0, animated: animated)
 		}
 
@@ -91,6 +84,12 @@ final class PreferencesTabViewController: NSViewController, PreferencesStyleCont
 		}
 	}
 
+	func restoreInitialTab() {
+		if activeTab == nil {
+			activateTab(index: 0, animated: false)
+		}
+	}
+
 	private func updateWindowTitle(tabIndex: Int) {
 		self.window.title = {
 			if preferencePanes.count > 1 {
@@ -114,6 +113,12 @@ final class PreferencesTabViewController: NSViewController, PreferencesStyleCont
 	}
 
 	private func animateTabTransition(index: Int, animated: Bool) {
+		guard let activeTab = activeTab else {
+			assertionFailure("animateTabTransition called before a tab was displayed; transition only works from one tab to another")
+			immediatelyDisplayTab(index: index)
+			return
+		}
+
 		let fromViewController = children[activeTab]
 		let toViewController = children[index]
 		let options: NSViewController.TransitionOptions = animated && isAnimated

Sources/Preferences/PreferencesWindowController.swift

@@ -74,15 +74,20 @@ public final class PreferencesWindowController: NSWindowController {
 	///
 	/// - See `close()` to close the window again.
 	/// - See `showWindow(_:)` to show the window without the convenience of activating the app.
-	/// - Note: Unless you need to open a specific pane, prefer not to pass a parameter at all
-	/// - Parameter preferencePane: Identifier of the preference pane to display.
+	/// - Note: Unless you need to open a specific pane, prefer not to pass a parameter at all or `nil`.
+	/// - Parameter preferencePane: Identifier of the preference pane to display, or `nil` to show the
+	///   tab that was open when the user last closed the window.
 	public func show(preferencePane preferenceIdentifier: PreferencePaneIdentifier? = nil) {
 		if !window!.isVisible {
 			window?.center()
 		}
 
 		showWindow(self)
-		tabViewController.activateTab(preferenceIdentifier: preferenceIdentifier, animated: false)
+		if let preferenceIdentifier = preferenceIdentifier {
+			tabViewController.activateTab(preferenceIdentifier: preferenceIdentifier, animated: false)
+		} else {
+			tabViewController.restoreInitialTab()
+		}
 		NSApp.activate(ignoringOtherApps: true)
 	}
 }