New API on TreeListView to retrieve parent item (#3355)

Fixing binding error on attached property

Author: Keboo

MaterialDesignThemes.Wpf.Tests/Internal/TreeListViewItemsCollectionTests.cs

@@ -591,6 +591,58 @@ public void Replace_TopLevelItem_IsReplaced(int indexToReplace)
         Assert.Equal(expectedExpanded, treeListViewItemsCollection.GetAllIsExpanded());
     }
 
+    [Theory]
+    [InlineData(-1)]
+    [InlineData(3)]
+    public void GetParent_WithInvalidIndex_ThrowsOutOfRangeException(int index)
+    {
+        //Arrange
+        ObservableCollection<string> boundCollection = new() { "0", "1", "2" };
+        TreeListViewItemsCollection<string> treeListViewItemsCollection = new(boundCollection);
+
+        //Act/Assert
+        var ex = Assert.Throws<ArgumentOutOfRangeException>(() => treeListViewItemsCollection.GetParent(index));
+        Assert.Equal("index", ex.ParamName);
+    }
+
+    [Fact]
+    public void GetParent_WithNestedItem_ReturnsParent()
+    {
+        //Arrange
+        ObservableCollection<string> boundCollection = new() { "0", "1", "2" };
+        TreeListViewItemsCollection<string> treeListViewItemsCollection = new(boundCollection);
+        treeListViewItemsCollection.InsertWithLevel(2, "1_0", 1);
+        treeListViewItemsCollection.InsertWithLevel(3, "1_1", 1);
+        treeListViewItemsCollection.InsertWithLevel(4, "1_2", 1);
+        treeListViewItemsCollection.InsertWithLevel(5, "1_2_0", 2);
+        treeListViewItemsCollection.InsertWithLevel(6, "1_2_1", 2);
+        treeListViewItemsCollection.InsertWithLevel(7, "1_2_2", 2);
+
+        /*
+         * 0. 0
+         * 1. 1
+         * 2.  1_0
+         * 3.  1_1
+         * 4.  1_2
+         * 5.    1_2_0
+         * 6.    1_2_1
+         * 7.    1_2_2
+         * 8. 2
+         */
+
+
+        //Act/Assert
+        Assert.Null(treeListViewItemsCollection.GetParent(0));
+        Assert.Null(treeListViewItemsCollection.GetParent(1));
+        Assert.Equal("1", treeListViewItemsCollection.GetParent(2));
+        Assert.Equal("1", treeListViewItemsCollection.GetParent(3));
+        Assert.Equal("1", treeListViewItemsCollection.GetParent(4));
+        Assert.Equal("1_2", treeListViewItemsCollection.GetParent(5));
+        Assert.Equal("1_2", treeListViewItemsCollection.GetParent(6));
+        Assert.Equal("1_2", treeListViewItemsCollection.GetParent(7));
+        Assert.Null(treeListViewItemsCollection.GetParent(8));
+    }
+
     private class TestableCollection<T> : ObservableCollection<T>
     {
         private int _blockCollectionChanges;

MaterialDesignThemes.Wpf/Internal/TreeListViewItemsCollection.cs

@@ -82,6 +82,21 @@ public void InsertWithLevel(int index, T item, int level)
         }
     }
 
+    public object? GetParent(int index)
+    {
+        if (index < 0 || index >= Count) throw new ArgumentOutOfRangeException(nameof(index));
+        int level = ItemLevels[index];
+        if (level == 0) return null;
+        for (int i = index - 1; i >= 0; i--)
+        {
+            if (ItemLevels[i] == level - 1)
+            {
+                return this[i];
+            }
+        }
+        return null;
+    }
+
     protected override void RemoveItem(int index)
     {
         int priorNonRootLevelItems = GetPriorNonRootLevelItemsCount(index);

MaterialDesignThemes.Wpf/Themes/MaterialDesignTheme.TreeListView.xaml

@@ -326,7 +326,7 @@
     </Setter>
     <Setter Property="VerticalContentAlignment" Value="{Binding VerticalContentAlignment, RelativeSource={RelativeSource AncestorType={x:Type ItemsControl}}}" />
     <Setter Property="wpf:TreeViewAssist.ExpanderSize" Value="16" />
-    <Setter Property="wpf:TreeViewAssist.HasNoItemsExpanderVisibility" Value="{Binding RelativeSource={RelativeSource AncestorType=TreeView}, Path=(wpf:TreeViewAssist.HasNoItemsExpanderVisibility)}" />
+    <Setter Property="wpf:TreeViewAssist.HasNoItemsExpanderVisibility" Value="{Binding RelativeSource={RelativeSource AncestorType=wpf:TreeListView}, Path=(wpf:TreeViewAssist.HasNoItemsExpanderVisibility)}" />
     <Setter Property="wpf:TreeViewAssist.ShowSelection" Value="True" />
   </Style>
 

MaterialDesignThemes.Wpf/TreeListView.cs

@@ -202,6 +202,18 @@ static int GetChildrenAndGrandChildrenCountOfPriorSiblings(TreeListViewItemsColl
         }
     }
 
+    public object? GetParent(object? item)
+    {
+        if (InternalItemsSource is { } itemSource &&
+            ItemContainerGenerator.ContainerFromItem(item) is { } container &&
+            ItemContainerGenerator.IndexFromContainer(container) is var index &&
+            index >= 0)
+        {
+            return itemSource.GetParent(index);
+        }
+        return null;
+    }
+
     private List<object?> GetExpandedChildrenAndGrandChildren(object? dataItem)
     {
         List<object?> expandedChildren = new();

MaterialDesignThemes.Wpf/TreeListViewItem.cs

@@ -112,12 +112,6 @@ internal void PrepareTreeListViewItem(object? item, TreeListView treeListView, i
         }
     }
 
-    protected override void OnContentChanged(object oldContent, object newContent)
-        => base.OnContentChanged(oldContent, newContent);
-
-    protected override void OnContentTemplateChanged(DataTemplate oldContentTemplate, DataTemplate newContentTemplate)
-        => base.OnContentTemplateChanged(oldContentTemplate, newContentTemplate);
-
     public override void OnApplyTemplate()
     {
         base.OnApplyTemplate();