Get X position from Columns.

For columnar layouts, there should usually be be no need to estimate the x position of the column start in the viewport, as this information can be queried from `IColumns`. Make a new `GetOrEstimateAnchorElementForViewport` virtual method and override its behavior for columnar presenters. Fixes #414
AvaloniaUI · Nov 27, 2024 · fed5361 · fed5361
1 parent 7b9571a
commit fed5361
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Showing 2 changed files with 25 additions and 5 deletions.
diff --git a/src/Avalonia.Controls.TreeDataGrid/Primitives/TreeDataGridColumnarPresenterBase.cs b/src/Avalonia.Controls.TreeDataGrid/Primitives/TreeDataGridColumnarPresenterBase.cs
@@ -23,6 +23,16 @@ protected sealed override Size GetInitialConstraint(Control element, int index,
             return new Size(Math.Min(availableSize.Width, column.MaxActualWidth), availableSize.Height);
         }
 
+        protected override (int index, double position) GetOrEstimateAnchorElementForViewport(
+            double viewportStart,
+            double viewportEnd,
+            int itemCount)
+        {
+            if (Columns?.GetColumnAt(viewportStart) is var (index, position) && index >= 0)
+                return (index, position);
+            return base.GetOrEstimateAnchorElementForViewport(viewportStart, viewportEnd, itemCount);
+        }
+
         protected sealed override bool NeedsFinalMeasurePass(int firstIndex, IReadOnlyList<Control?> elements)
         {
             var columns = Columns!;

diff --git a/src/Avalonia.Controls.TreeDataGrid/Primitives/TreeDataGridPresenterBase.cs b/src/Avalonia.Controls.TreeDataGrid/Primitives/TreeDataGridPresenterBase.cs
@@ -397,6 +397,20 @@ protected override Size ArrangeOverride(Size finalSize)
             }
         }
 
+        protected virtual (int index, double position) GetOrEstimateAnchorElementForViewport(
+            double viewportStart,
+            double viewportEnd,
+            int itemCount)
+        {
+            Debug.Assert(_realizedElements is not null);
+
+            return _realizedElements.GetOrEstimateAnchorElementForViewport(
+                viewportStart,
+                viewportEnd,
+                itemCount,
+                ref _lastEstimatedElementSizeU);
+        }
+
         protected override void OnAttachedToVisualTree(VisualTreeAttachmentEventArgs e)
         {
             base.OnAttachedToVisualTree(e);
@@ -539,11 +553,7 @@ private MeasureViewport CalculateMeasureViewport(IReadOnlyList<TItem> items, Siz
 
             // Get or estimate the anchor element from which to start realization.
             var itemCount = items.Count;
-            var (anchorIndex, anchorU) = _realizedElements.GetOrEstimateAnchorElementForViewport(
-                viewportStart,
-                viewportEnd,
-                itemCount,
-                ref _lastEstimatedElementSizeU);
+            var (anchorIndex, anchorU) = GetOrEstimateAnchorElementForViewport(viewportStart, viewportEnd, itemCount);
 
             // Check if the anchor element is not within the currently realized elements.
             var disjunct = anchorIndex < _realizedElements.FirstIndex ||