Fixes #2789. StatusItem should have a disabled attribute if it can't execute.

Terminal.Gui/Views/StatusBar.cs

@@ -27,11 +27,13 @@ public class StatusItem {
 		/// <param name="shortcut">Shortcut to activate the <see cref="StatusItem"/>.</param>
 		/// <param name="title">Title for the <see cref="StatusItem"/>.</param>
 		/// <param name="action">Action to invoke when the <see cref="StatusItem"/> is activated.</param>
-		public StatusItem (Key shortcut, ustring title, Action action)
+		/// <param name="canExecute">Function to determine if the action can currently be executed.</param>
+		public StatusItem (Key shortcut, ustring title, Action action, Func<bool> canExecute = null)
 		{
 			Title = title ?? "";
 			Shortcut = shortcut;
 			Action = action;
+			CanExecute = canExecute;
 		}
 
 		/// <summary>
@@ -54,7 +56,22 @@ public StatusItem (Key shortcut, ustring title, Action action)
 		/// Gets or sets the action to be invoked when the statusbar item is triggered
 		/// </summary>
 		/// <value>Action to invoke.</value>
-		public Action Action { get; }
+		public Action Action { get; set; }
+
+		/// <summary>
+		/// Gets or sets the action to be invoked to determine if the <see cref="StatusItem"/> can be triggered. 
+		/// If <see cref="CanExecute"/> returns <see langword="true"/> the status item will be enabled. Otherwise, it will be disabled.
+		/// </summary>
+		/// <value>Function to determine if the action is can be executed or not.</value>
+		public Func<bool> CanExecute { get; set; }
+
+		/// <summary>
+		/// Returns <see langword="true"/> if the status item is enabled. This method is a wrapper around <see cref="CanExecute"/>.
+		/// </summary>
+		public bool IsEnabled ()
+		{
+			return CanExecute == null ? true : CanExecute ();
+		}
 
 		/// <summary>
 		/// Gets or sets arbitrary data for the status item.
@@ -116,6 +133,17 @@ Attribute ToggleScheme (Attribute scheme)
 			return result;
 		}
 
+		Attribute DetermineColorSchemeFor (StatusItem item)
+		{
+			if (item != null) {
+				if (item.IsEnabled ()) {
+					return GetNormalColor ();
+				}
+				return ColorScheme.Disabled;
+			}
+			return GetNormalColor ();
+		}
+
 		///<inheritdoc/>
 		public override void Redraw (Rect bounds)
 		{
@@ -129,9 +157,12 @@ public override void Redraw (Rect bounds)
 			Driver.SetAttribute (scheme);
 			for (int i = 0; i < Items.Length; i++) {
 				var title = Items [i].Title.ToString ();
+				Driver.SetAttribute (DetermineColorSchemeFor (Items [i]));
 				for (int n = 0; n < Items [i].Title.RuneCount; n++) {
 					if (title [n] == '~') {
-						scheme = ToggleScheme (scheme);
+						if (Items [i].IsEnabled ()) {
+							scheme = ToggleScheme (scheme);
+						}
 						continue;
 					}
 					Driver.AddRune (title [n]);
@@ -149,7 +180,9 @@ public override bool ProcessHotKey (KeyEvent kb)
 		{
 			foreach (var item in Items) {
 				if (kb.Key == item.Shortcut) {
-					Run (item.Action);
+					if (item.IsEnabled ()) {
+						Run (item.Action);
+					}
 					return true;
 				}
 			}
@@ -165,7 +198,10 @@ public override bool MouseEvent (MouseEvent me)
 			int pos = 1;
 			for (int i = 0; i < Items.Length; i++) {
 				if (me.X >= pos && me.X < pos + GetItemTitleLength (Items [i].Title)) {
-					Run (Items [i].Action);
+					var item = Items [i];
+					if (item.IsEnabled ()) {
+						Run (item.Action);
+					}
 					break;
 				}
 				pos += GetItemTitleLength (Items [i].Title) + 3;

UnitTests/Views/StatusBarTests.cs

@@ -18,12 +18,13 @@ public void StatusItem_Constructor ()
 			Assert.Equal (Key.CtrlMask | Key.Q, si.Shortcut);
 			Assert.Equal ("~^Q~ Quit", si.Title);
 			Assert.Null (si.Action);
+			Assert.True (si.IsEnabled ());
 			si = new StatusItem (Key.CtrlMask | Key.Q, "~^Q~ Quit", () => { });
 			Assert.NotNull (si.Action);
 		}
 
 		[Fact]
-		public void StatusBar_Contructor_Default ()
+		public void StatusBar_Constructor_Default ()
 		{
 			var sb = new StatusBar ();
 
@@ -155,5 +156,43 @@ public void AddItemAt_RemoveItem_Replacing ()
 			Assert.Equal ("~^A~ Save As", sb.Items [1].Title);
 			Assert.Equal ("~^Q~ Quit", sb.Items [^1].Title);
 		}
+
+		[Fact, AutoInitShutdown]
+		public void CanExecute_ProcessHotKey ()
+		{
+			Window win = null;
+			var statusBar = new StatusBar (new StatusItem [] {
+				new StatusItem (Key.CtrlMask | Key.N, "~^N~ New", New, CanExecuteNew),
+				new StatusItem (Key.CtrlMask | Key.C, "~^C~ Close", Close, CanExecuteClose)
+			});
+			var top = Application.Top;
+			top.Add (statusBar);
+
+			bool CanExecuteNew () => win == null;
+
+			void New ()
+			{
+				win = new Window ();
+			}
+
+			bool CanExecuteClose () => win != null;
+
+			void Close ()
+			{
+				win = null;
+			}
+
+			Application.Begin (top);
+
+			Assert.Null (win);
+			Assert.True (CanExecuteNew ());
+			Assert.False (CanExecuteClose ());
+
+			Assert.True (top.ProcessHotKey (new KeyEvent (Key.N | Key.CtrlMask, new KeyModifiers () { Alt = true })));
+			Application.MainLoop.MainIteration ();
+			Assert.NotNull (win);
+			Assert.False (CanExecuteNew ());
+			Assert.True (CanExecuteClose ());
+		}
 	}
 }