Improve text selection

Author: timunie

src/MahApps.Metro/Controls/MultiSelectionComboBox/MultiSelectionComboBox.cs

@@ -63,6 +63,7 @@ public MultiSelectionComboBox()
         private ListBox? PART_SelectedItemsPresenter;
 
         private bool isUserdefinedTextInputPending;
+        private bool isTextChanging; // This flag indicates if the text is changed by us, so we don't want to refire the TextChangedEvent.
         private bool shouldDoTextReset; // Defines if the Text should be reset after selecting items from string
         private bool shouldAddItems; // Defines if the MSCB should add new items from text input. Don't set this to true while input is pending. We cannot know how long the user needs for typing.
         private bool IsSyncingSelectedItems; // true if syncing in one or the other direction already running
@@ -553,14 +554,17 @@ public void ResetEditableText()
         /// <summary>
         /// Updates the Text of the editable TextBox.
         /// Sets the custom Text if any otherwise the concatenated string.
-        /// </summary>
+        /// </summary> 
+
         private void UpdateEditableText(bool forceUpdate = false)
         {
             if (this.PART_EditableTextBox is null || (this.PART_EditableTextBox.IsKeyboardFocused && !forceUpdate))
             {
                 return;
             }
 
+            this.isTextChanging = true;
+
             var oldSelectionStart = this.PART_EditableTextBox.SelectionStart;
             var oldSelectionLength = this.PART_EditableTextBox.SelectionLength;
             var oldTextLength = this.PART_EditableTextBox.Text.Length;
@@ -588,6 +592,8 @@ private void UpdateEditableText(bool forceUpdate = false)
                 this.PART_EditableTextBox.SelectionStart = oldSelectionStart;
                 this.PART_EditableTextBox.SelectionLength = oldSelectionLength;
             }
+
+            this.isTextChanging = false;
         }
 
         private void UpdateDisplaySelectedItems()
@@ -654,7 +660,7 @@ private void UpdateDisplaySelectedItems(SelectedItemsOrderType selectedItemsOrde
 
         private void SelectItemsFromText(int millisecondsToWait)
         {
-            if (!this.isUserdefinedTextInputPending)
+            if (!this.isUserdefinedTextInputPending || this.isTextChanging)
             {
                 return;
             }
@@ -746,10 +752,16 @@ private void UpdateSelectedItemsFromTextTimer_Tick(object sender, EventArgs e)
 
                 case SelectionMode.Multiple:
                 case SelectionMode.Extended:
+                    if (this.SelectedItems is null)
+                    {
+                        break; // Exit here if we have no SelectedItems yet
+                    }
+
                     var strings = !string.IsNullOrEmpty(this.Separator) ? this.Text?.Split(new[] { this.Separator }, StringSplitOptions.RemoveEmptyEntries) : null;
 
-                    // clear items here, so we can use the text before.
-                    this.SelectedItems?.Clear();
+                    int position = 0;
+
+                    // this.SelectedItems?.Clear();
 
                     if (strings is not null)
                     {
@@ -762,8 +774,27 @@ private void UpdateSelectedItemsFromTextTimer_Tick(object sender, EventArgs e)
                                 {
                                     if (this.ObjectToStringComparer.CheckIfStringMatchesObject(stringObject, item, this.EditableTextStringComparision, this.SelectedItemStringFormat))
                                     {
-                                        this.SelectedItems?.Add(item);
-                                        foundItem = true;
+                                        var oldPosition = this.SelectedItems.IndexOf(item);
+
+                                        if (oldPosition < 0) // if old index is <0 the item is not in list yet. let's add it.
+                                        {
+                                            this.SelectedItems.Insert(position,item);
+                                            foundItem = true;
+                                            position++;
+                                        }
+                                        else if (oldPosition > position) // if the item has a wrong position in list we need to swap it accordingly.
+                                        {
+                                            this.SelectedItems.RemoveAt(oldPosition);
+                                            this.SelectedItems.Insert(position, item);
+
+                                            foundItem = true;
+                                            position++;
+                                        }
+                                        else if (oldPosition == position)
+                                        {
+                                            foundItem = true;
+                                            position++;
+                                        }
                                     }
                                 }
                             }
@@ -772,7 +803,8 @@ private void UpdateSelectedItemsFromTextTimer_Tick(object sender, EventArgs e)
                             {
                                 if (this.shouldAddItems && this.TryAddObjectFromString(stringObject, out var result))
                                 {
-                                    this.SelectedItems?.Add(result);
+                                    this.SelectedItems.Insert(position,result);
+                                    position++;
                                 }
                                 else
                                 {
@@ -782,6 +814,12 @@ private void UpdateSelectedItemsFromTextTimer_Tick(object sender, EventArgs e)
                         }
                     }
 
+                    // Remove Items if needed.
+                    while (this.SelectedItems.Count > position)
+                    {
+                        this.SelectedItems.RemoveAt(position);
+                    }
+
                     break;
 
                 default:
@@ -865,9 +903,9 @@ private bool TryAddObjectFromString(string? input, out object? result)
             }
         }
 
-        #endregion
+#endregion
 
-        #region Commands
+#region Commands
 
         // Clear Text Command
         public static RoutedUICommand ClearContentCommand { get; } = new RoutedUICommand("ClearContent", nameof(ClearContentCommand), typeof(MultiSelectionComboBox));
@@ -935,9 +973,9 @@ private static void RemoveItemCommand_CanExecute(object sender, CanExecuteRouted
             }
         }
 
-        #endregion
+#endregion
 
-        #region Overrides
+#region Overrides
 
         public override void OnApplyTemplate()
         {
@@ -966,6 +1004,8 @@ public override void OnApplyTemplate()
             {
                 selectedItemsCollection.CollectionChanged -= this.PART_PopupListBox_SelectedItems_CollectionChanged;
                 selectedItemsCollection.CollectionChanged += this.PART_PopupListBox_SelectedItems_CollectionChanged;
+
+                PART_PopupListBox.Unloaded += (s, e) => { selectedItemsCollection.CollectionChanged -= this.PART_PopupListBox_SelectedItems_CollectionChanged; };
             }
 
             // Do update the text 
@@ -985,8 +1025,8 @@ private void PART_PopupListBox_SelectedItems_CollectionChanged(object sender, No
         protected override void OnSelectionChanged(SelectionChangedEventArgs e)
         {
             base.OnSelectionChanged(e);
-            this.UpdateEditableText();
             this.UpdateDisplaySelectedItems();
+            this.UpdateEditableText();
         }
 
         private void MultiSelectionComboBox_Loaded(object sender, EventArgs e)
@@ -1112,7 +1152,7 @@ private void MoveFocusToDropDown()
             }
 
             var index = this.PART_PopupListBox.SelectedIndex;
-            if (index < 0)
+            if (index < 0 && this.PART_PopupListBox.Items.Count > 0)
             {
                 index = 0;
             }
@@ -1527,16 +1567,21 @@ private bool IsSelectableHelper(object o)
             return (bool)d.GetValue(IsEnabledProperty);
         }
 
-        #endregion
+#endregion
 
-        #region Events
+#region Events
 
 #if NET5_0_OR_GREATER
         private void SelectedItemsImpl_CollectionChanged(object? sender, NotifyCollectionChangedEventArgs e)
 #else
         private void SelectedItemsImpl_CollectionChanged(object sender, NotifyCollectionChangedEventArgs e)
 #endif
         {
+            if (this.PART_PopupListBox is null)
+            {
+                this.ApplyTemplate();
+            }
+
             this.SyncSelectedItems(sender as IList, this.PART_PopupListBox?.SelectedItems, e);
         }
 
@@ -1672,7 +1717,7 @@ private static void UpdateText(DependencyObject d, DependencyPropertyChangedEven
 
         private static void OnTextChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
         {
-            if (d is MultiSelectionComboBox multiSelectionComboBox)
+            if (d is MultiSelectionComboBox multiSelectionComboBox && !multiSelectionComboBox.isTextChanging)
             {
                 multiSelectionComboBox.UpdateHasCustomText(null);
                 multiSelectionComboBox.isUserdefinedTextInputPending = true;
@@ -1720,6 +1765,6 @@ public event AddedItemEventArgsHandler AddedItem
             remove => this.RemoveHandler(AddedItemEvent, value);
         }
 
-        #endregion
+#endregion
     }
 }