When trying to delete a referenced view, give feedback about the error

Author: tznind

src/Operations/DeleteViewOperation.cs

@@ -13,6 +13,12 @@ public class DeleteViewOperation : Operation
     private readonly View[] from;
     private readonly Design[] originalSelection;
 
+
+    /// <summary>
+    /// Views which reference the <see cref="Design"/> being operated on
+    /// </summary>
+    public Design[] PreventDeleting { get; set; }
+
     /// <summary>
     /// Initializes a new instance of the <see cref="DeleteViewOperation"/> class.
     /// </summary>
@@ -34,7 +40,9 @@ public DeleteViewOperation(params Design[] delete)
 
             // there are view(s) that depend on us (e.g. for positioning)
             // that are not also being deleted themselves
-            if (design.GetDependantDesigns().Any(dep => !delete.Contains(dep)))
+            PreventDeleting = design.GetDependantDesigns().Where(dep => !delete.Contains(dep)).ToArray();
+            
+            if (PreventDeleting.Length > 0)
             {
                 // Prevent deleting - so there are no orphan references from existing Views e.g. Pos.Right(thingIJustDeleted);
                 this.IsImpossible = true;

src/UI/Editor.cs

@@ -61,6 +61,11 @@ public class Editor : Toplevel
     /// </summary>
     public static bool Quiet = false;
 
+    /// <summary>
+    /// Start your message with this if you want it to be visually highlighted as bad.
+    /// </summary>
+    public const string Error = "Error";
+
     /// <summary>
     /// Initializes a new instance of the <see cref="Editor"/> class.
     /// </summary>
@@ -293,6 +298,13 @@ protected override void OnDrawComplete(DrawContext? context)
             // and have a designable view focused
             if (toDisplay != null)
             {
+                var before = GetCurrentAttribute();
+
+                if (toDisplay.StartsWith(Error))
+                {
+                    SetAttribute(new Attribute(Color.Red, Color.Black));
+                }
+
                 // write its name in the lower right
                 int y = this.GetContentSize().Height - 1;
                 int right = bounds.Width - 1;
@@ -303,6 +315,8 @@ protected override void OnDrawComplete(DrawContext? context)
                 {
                     this.AddRune(right - len + i, y, runes[i]);
                 }
+
+                SetAttribute(before);
             }
         }
 
@@ -1151,10 +1165,31 @@ private void Delete()
         if (SelectionManager.Instance.Selected.Any())
         {
             var cmd = new DeleteViewOperation(SelectionManager.Instance.Selected.ToArray());
+            
+            
+            if (cmd.IsImpossible && cmd.PreventDeleting.Any())
+            {
+                ShowErrorThatViewIsUsedByOthers(cmd.PreventDeleting);
+                return;
+            }
+
             OperationManager.Instance.Do(cmd);
         }
     }
 
+    private void ShowErrorThatViewIsUsedByOthers(Design[] usedBy)
+    {
+        if (usedBy.Length == 1)
+        {
+            flashMessage = $"{Error}, view referenced by " + usedBy[0].FieldName;
+        }
+        else
+        {
+            flashMessage = $"{Error}, view referenced by {usedBy.Length} views";
+        }
+        this.SetNeedsDraw();
+    }
+
     private void DoForSelectedViews(Func<Design, Operation> operationFunc, bool allowOnRoot = false)
     {
         if (this.viewBeingEdited == null)