A bug with Grid and InvalidateArrange call (which probably cause problems in TransitioningContentControl)

[deryaza]

If you take ReactiveUIDemo and apply this patch
0002-bug.patch

This fill fail with the following exception:

Details

System.NullReferenceException: Object reference not set to an instance of an object.
   at Avalonia.Controls.Grid.ArrangeOverride(Size arrangeSize) in C:\Users\デリャザ\source\repos\Avalonia\src\Avalonia.Controls\Grid.cs:line 526
   at Avalonia.Layout.Layoutable.ArrangeCore(Rect finalRect) in C:\Users\デリャザ\source\repos\Avalonia\src\Avalonia.Base\Layout\Layoutable.cs:line 669
   at Avalonia.Layout.Layoutable.Arrange(Rect rect) in C:\Users\デリャザ\source\repos\Avalonia\src\Avalonia.Base\Layout\Layoutable.cs:line 418
   at Avalonia.Controls.Presenters.ContentPresenter.ArrangeOverrideImpl(Size finalSize, Vector offset) in C:\Users\デリャザ\source\repos\Avalonia\src\Avalonia.Controls\Presenters\ContentPresenter.cs:line 660
   at Avalonia.Controls.Presenters.ContentPresenter.ArrangeOverride(Size finalSize) in C:\Users\デリャザ\source\repos\Avalonia\src\Avalonia.Controls\Presenters\ContentPresenter.cs:line 589
   at Avalonia.Layout.Layoutable.ArrangeCore(Rect finalRect) in C:\Users\デリャザ\source\repos\Avalonia\src\Avalonia.Base\Layout\Layoutable.cs:line 669
   at Avalonia.Layout.Layoutable.Arrange(Rect rect) in C:\Users\デリャザ\source\repos\Avalonia\src\Avalonia.Base\Layout\Layoutable.cs:line 418
   at Avalonia.Layout.Layoutable.ArrangeOverride(Size finalSize) in C:\Users\デリャザ\source\repos\Avalonia\src\Avalonia.Base\Layout\Layoutable.cs:line 721
   at Avalonia.Layout.Layoutable.ArrangeCore(Rect finalRect) in C:\Users\デリャザ\source\repos\Avalonia\src\Avalonia.Base\Layout\Layoutable.cs:line 669
   at Avalonia.Layout.Layoutable.Arrange(Rect rect) in C:\Users\デリャザ\source\repos\Avalonia\src\Avalonia.Base\Layout\Layoutable.cs:line 418
   at Avalonia.Controls.Presenters.ContentPresenter.ArrangeOverrideImpl(Size finalSize, Vector offset) in C:\Users\デリャザ\source\repos\Avalonia\src\Avalonia.Controls\Presenters\ContentPresenter.cs:line 660
   at Avalonia.Controls.Presenters.ContentPresenter.ArrangeOverride(Size finalSize) in C:\Users\デリャザ\source\repos\Avalonia\src\Avalonia.Controls\Presenters\ContentPresenter.cs:line 589
   at Avalonia.Layout.Layoutable.ArrangeCore(Rect finalRect) in C:\Users\デリャザ\source\repos\Avalonia\src\Avalonia.Base\Layout\Layoutable.cs:line 669
   at Avalonia.Layout.Layoutable.Arrange(Rect rect) in C:\Users\デリャザ\source\repos\Avalonia\src\Avalonia.Base\Layout\Layoutable.cs:line 418
   at Avalonia.Layout.Layoutable.ArrangeOverride(Size finalSize) in C:\Users\デリャザ\source\repos\Avalonia\src\Avalonia.Base\Layout\Layoutable.cs:line 721
   at Avalonia.Layout.Layoutable.ArrangeCore(Rect finalRect) in C:\Users\デリャザ\source\repos\Avalonia\src\Avalonia.Base\Layout\Layoutable.cs:line 669
   at Avalonia.Layout.Layoutable.Arrange(Rect rect) in C:\Users\デリャザ\source\repos\Avalonia\src\Avalonia.Base\Layout\Layoutable.cs:line 418
   at Avalonia.Layout.Layoutable.ArrangeOverride(Size finalSize) in C:\Users\デリャザ\source\repos\Avalonia\src\Avalonia.Base\Layout\Layoutable.cs:line 721
   at Avalonia.Controls.TransitioningContentControl.ArrangeOverride(Size finalSize) in C:\Users\デリャザ\source\repos\Avalonia\src\Avalonia.Controls\TransitioningContentControl.cs:line 59
   at Avalonia.Layout.Layoutable.ArrangeCore(Rect finalRect) in C:\Users\デリャザ\source\repos\Avalonia\src\Avalonia.Base\Layout\Layoutable.cs:line 669
   at Avalonia.Layout.Layoutable.Arrange(Rect rect) in C:\Users\デリャザ\source\repos\Avalonia\src\Avalonia.Base\Layout\Layoutable.cs:line 418
   at Avalonia.Controls.StackPanel.ArrangeChild(Control child, Rect rect, Size panelSize, Orientation orientation) in C:\Users\デリャザ\source\repos\Avalonia\src\Avalonia.Controls\StackPanel.cs:line 355
   at Avalonia.Controls.StackPanel.ArrangeOverride(Size finalSize) in C:\Users\デリャザ\source\repos\Avalonia\src\Avalonia.Controls\StackPanel.cs:line 341
   at Avalonia.Layout.Layoutable.ArrangeCore(Rect finalRect) in C:\Users\デリャザ\source\repos\Avalonia\src\Avalonia.Base\Layout\Layoutable.cs:line 669
   at Avalonia.Layout.Layoutable.Arrange(Rect rect) in C:\Users\デリャザ\source\repos\Avalonia\src\Avalonia.Base\Layout\Layoutable.cs:line 418
   at Avalonia.Controls.Presenters.ContentPresenter.ArrangeOverrideImpl(Size finalSize, Vector offset) in C:\Users\デリャザ\source\repos\Avalonia\src\Avalonia.Controls\Presenters\ContentPresenter.cs:line 660
   at Avalonia.Controls.Presenters.ScrollContentPresenter.ArrangeWithAnchoring(Size finalSize) in C:\Users\デリャザ\source\repos\Avalonia\src\Avalonia.Controls\Presenters\ScrollContentPresenter.cs:line 472
   at Avalonia.Controls.Presenters.ScrollContentPresenter.ArrangeOverride(Size finalSize) in C:\Users\デリャザ\source\repos\Avalonia\src\Avalonia.Controls\Presenters\ScrollContentPresenter.cs:line 401
   at Avalonia.Layout.Layoutable.ArrangeCore(Rect finalRect) in C:\Users\デリャザ\source\repos\Avalonia\src\Avalonia.Base\Layout\Layoutable.cs:line 669
   at Avalonia.Layout.Layoutable.Arrange(Rect rect) in C:\Users\デリャザ\source\repos\Avalonia\src\Avalonia.Base\Layout\Layoutable.cs:line 418
   at Avalonia.Controls.Grid.ArrangeOverride(Size arrangeSize) in C:\Users\デリャザ\source\repos\Avalonia\src\Avalonia.Controls\Grid.cs:line 549
   at Avalonia.Layout.Layoutable.ArrangeCore(Rect finalRect) in C:\Users\デリャザ\source\repos\Avalonia\src\Avalonia.Base\Layout\Layoutable.cs:line 669
   at Avalonia.Layout.Layoutable.Arrange(Rect rect) in C:\Users\デリャザ\source\repos\Avalonia\src\Avalonia.Base\Layout\Layoutable.cs:line 418
   at Avalonia.Layout.Layoutable.ArrangeOverride(Size finalSize) in C:\Users\デリャザ\source\repos\Avalonia\src\Avalonia.Base\Layout\Layoutable.cs:line 721
   at Avalonia.Layout.Layoutable.ArrangeCore(Rect finalRect) in C:\Users\デリャザ\source\repos\Avalonia\src\Avalonia.Base\Layout\Layoutable.cs:line 669
   at Avalonia.Layout.Layoutable.Arrange(Rect rect) in C:\Users\デリャザ\source\repos\Avalonia\src\Avalonia.Base\Layout\Layoutable.cs:line 418
   at Avalonia.Controls.Presenters.ContentPresenter.ArrangeOverrideImpl(Size finalSize, Vector offset) in C:\Users\デリャザ\source\repos\Avalonia\src\Avalonia.Controls\Presenters\ContentPresenter.cs:line 660
   at Avalonia.Controls.Presenters.ContentPresenter.ArrangeOverride(Size finalSize) in C:\Users\デリャザ\source\repos\Avalonia\src\Avalonia.Controls\Presenters\ContentPresenter.cs:line 589
   at Avalonia.Layout.Layoutable.ArrangeCore(Rect finalRect) in C:\Users\デリャザ\source\repos\Avalonia\src\Avalonia.Base\Layout\Layoutable.cs:line 669
   at Avalonia.Layout.Layoutable.Arrange(Rect rect) in C:\Users\デリャザ\source\repos\Avalonia\src\Avalonia.Base\Layout\Layoutable.cs:line 418
   at Avalonia.Layout.LayoutHelper.ArrangeChildInternal(Layoutable child, Size availableSize, Thickness padding) in C:\Users\デリャザ\source\repos\Avalonia\src\Avalonia.Base\Layout\LayoutHelper.cs:line 91
   at Avalonia.Layout.LayoutHelper.ArrangeChild(Layoutable child, Size availableSize, Thickness padding) in C:\Users\デリャザ\source\repos\Avalonia\src\Avalonia.Base\Layout\LayoutHelper.cs:line 86
   at Avalonia.Controls.Decorator.ArrangeOverride(Size finalSize) in C:\Users\デリャザ\source\repos\Avalonia\src\Avalonia.Controls\Decorator.cs:line 60
   at Avalonia.Controls.Primitives.VisualLayerManager.ArrangeOverride(Size finalSize) in C:\Users\デリャザ\source\repos\Avalonia\src\Avalonia.Controls\Primitives\VisualLayerManager.cs:line 161
   at Avalonia.Layout.Layoutable.ArrangeCore(Rect finalRect) in C:\Users\デリャザ\source\repos\Avalonia\src\Avalonia.Base\Layout\Layoutable.cs:line 669
   at Avalonia.Layout.Layoutable.Arrange(Rect rect) in C:\Users\デリャザ\source\repos\Avalonia\src\Avalonia.Base\Layout\Layoutable.cs:line 418
   at Avalonia.Layout.Layoutable.ArrangeOverride(Size finalSize) in C:\Users\デリャザ\source\repos\Avalonia\src\Avalonia.Base\Layout\Layoutable.cs:line 721
   at Avalonia.Layout.Layoutable.ArrangeCore(Rect finalRect) in C:\Users\デリャザ\source\repos\Avalonia\src\Avalonia.Base\Layout\Layoutable.cs:line 669
   at Avalonia.Layout.Layoutable.Arrange(Rect rect) in C:\Users\デリャザ\source\repos\Avalonia\src\Avalonia.Base\Layout\Layoutable.cs:line 418
   at Avalonia.Layout.Layoutable.ArrangeOverride(Size finalSize) in C:\Users\デリャザ\source\repos\Avalonia\src\Avalonia.Base\Layout\Layoutable.cs:line 721
   at Avalonia.Controls.WindowBase.ArrangeCore(Rect finalRect) in C:\Users\デリャザ\source\repos\Avalonia\src\Avalonia.Controls\WindowBase.cs:line 296
   at Avalonia.Layout.Layoutable.Arrange(Rect rect) in C:\Users\デリャザ\source\repos\Avalonia\src\Avalonia.Base\Layout\Layoutable.cs:line 418
   at Avalonia.Layout.LayoutManager.Arrange(Layoutable control) in C:\Users\デリャザ\source\repos\Avalonia\src\Avalonia.Base\Layout\LayoutManager.cs:line 334
   at Avalonia.Layout.LayoutManager.Arrange(Layoutable control) in C:\Users\デリャザ\source\repos\Avalonia\src\Avalonia.Base\Layout\LayoutManager.cs:line 322
   at Avalonia.Layout.LayoutManager.Arrange(Layoutable control) in C:\Users\デリャザ\source\repos\Avalonia\src\Avalonia.Base\Layout\LayoutManager.cs:line 322
   at Avalonia.Layout.LayoutManager.Arrange(Layoutable control) in C:\Users\デリャザ\source\repos\Avalonia\src\Avalonia.Base\Layout\LayoutManager.cs:line 322
   at Avalonia.Layout.LayoutManager.Arrange(Layoutable control) in C:\Users\デリャザ\source\repos\Avalonia\src\Avalonia.Base\Layout\LayoutManager.cs:line 322
   at Avalonia.Layout.LayoutManager.Arrange(Layoutable control) in C:\Users\デリャザ\source\repos\Avalonia\src\Avalonia.Base\Layout\LayoutManager.cs:line 322
   at Avalonia.Layout.LayoutManager.Arrange(Layoutable control) in C:\Users\デリャザ\source\repos\Avalonia\src\Avalonia.Base\Layout\LayoutManager.cs:line 322
   at Avalonia.Layout.LayoutManager.Arrange(Layoutable control) in C:\Users\デリャザ\source\repos\Avalonia\src\Avalonia.Base\Layout\LayoutManager.cs:line 322
   at Avalonia.Layout.LayoutManager.Arrange(Layoutable control) in C:\Users\デリャザ\source\repos\Avalonia\src\Avalonia.Base\Layout\LayoutManager.cs:line 322
   at Avalonia.Layout.LayoutManager.Arrange(Layoutable control) in C:\Users\デリャザ\source\repos\Avalonia\src\Avalonia.Base\Layout\LayoutManager.cs:line 322
   at Avalonia.Layout.LayoutManager.ExecuteArrangePass() in C:\Users\デリャザ\source\repos\Avalonia\src\Avalonia.Base\Layout\LayoutManager.cs:line 272
   at Avalonia.Layout.LayoutManager.InnerLayoutPass() in C:\Users\デリャザ\source\repos\Avalonia\src\Avalonia.Base\Layout\LayoutManager.cs:line 240
   at Avalonia.Layout.LayoutManager.ExecuteLayoutPass() in C:\Users\デリャザ\source\repos\Avalonia\src\Avalonia.Base\Layout\LayoutManager.cs:line 151
   at Avalonia.Layout.LayoutManager.ExecuteQueuedLayoutPass() in C:\Users\デリャザ\source\repos\Avalonia\src\Avalonia.Base\Layout\LayoutManager.cs:line 111
   at Avalonia.Media.MediaContext.FireInvokeOnRenderCallbacks() in C:\Users\デリャザ\source\repos\Avalonia\src\Avalonia.Base\Media\MediaContext.cs:line 198
   at Avalonia.Media.MediaContext.RenderCore() in C:\Users\デリャザ\source\repos\Avalonia\src\Avalonia.Base\Media\MediaContext.cs:line 135
   at Avalonia.Media.MediaContext.Render() in C:\Users\デリャザ\source\repos\Avalonia\src\Avalonia.Base\Media\MediaContext.cs:line 116
   at Avalonia.Threading.DispatcherOperation.InvokeCore() in C:\Users\デリャザ\source\repos\Avalonia\src\Avalonia.Base\Threading\DispatcherOperation.cs:line 274

Basically, exception happens like this:

1. MeasureOverride happens. Since extData is null, it doesn't call ValidateDefinitionsUStructure that creates DefinitionsU.
2. OnLoaded event happens where access to RowDefinitions creates _extData
3. ArrangeOverride happens and now it falls into different branch of if (_extData is null) where it expects to have Debug.Assert(DefinitionsU.Count > 0 && DefinitionsV.Count > 0); initialized from MeasureOverride call.

[timunie]

@deryaza can you check with the recent build from #13518 ? The build ID should be 41664 of the avalonia-all feed.

[timunie]

/cc @laolarou726

[deryaza]

@timunie no, I think I have a different issue (tested, doesn't fix it)

[deryaza]

A bit different, but a smaller repro (I guess InvalidateArrange is culprit in TransitioningContentControl):

using Avalonia.Controls;
using Avalonia.Markup.Xaml;

namespace ReactiveUIDemo
{
    public class MainWindow : Window
    {
        public MainWindow()
        {
            this.InitializeComponent();
            var panel = this.FindControl<StackPanel>("Panel");
            var button = this.FindControl<Button>("Button");
            var button2 = this.FindControl<Button>("Button2");
            var grid = new Grid();
            grid.Loaded += (sender, args) => _ = ((Grid)sender).RowDefinitions;
            button.Click += (sender, args) =>
            {
                panel.Children.Add(grid);
            };
            button2.Click += (sender, args) =>
            {
                grid.InvalidateArrange();
            };
        }

        private void InitializeComponent()
        {
            AvaloniaXamlLoader.Load(this);
        }
    }
}

<Window
    Title="AvaloniaUI ReactiveUI Demo"
    x:Class="ReactiveUIDemo.MainWindow"
    x:DataType="vm:MainWindowViewModel"
    xmlns="https://github.com/avaloniaui"
    xmlns:rxui="using:Avalonia.ReactiveUI"
    xmlns:vm="using:ReactiveUIDemo.ViewModels"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
    <StackPanel x:Name="Panel">
        <Button x:Name="Button">crash</Button>
        <Button x:Name="Button2">crash2</Button>
    </StackPanel>
</Window>

[laolarou726]

A bit different, but a smaller repro (I guess InvalidateArrange is culprit in TransitioningContentControl):

using Avalonia.Controls;

using Avalonia.Markup.Xaml;



namespace ReactiveUIDemo

{

    public class MainWindow : Window

    {

        public MainWindow()

        {

            this.InitializeComponent();

            var panel = this.FindControl<StackPanel>("Panel");

            var button = this.FindControl<Button>("Button");

            var button2 = this.FindControl<Button>("Button2");

            var grid = new Grid();

            grid.Loaded += (sender, args) => _ = ((Grid)sender).RowDefinitions;

            button.Click += (sender, args) =>

            {

                panel.Children.Add(grid);

            };

            button2.Click += (sender, args) =>

            {

                grid.InvalidateArrange();

            };

        }



        private void InitializeComponent()

        {

            AvaloniaXamlLoader.Load(this);

        }

    }

}

<Window

    Title="AvaloniaUI ReactiveUI Demo"

    x:Class="ReactiveUIDemo.MainWindow"

    x:DataType="vm:MainWindowViewModel"

    xmlns="https://github.com/avaloniaui"

    xmlns:rxui="using:Avalonia.ReactiveUI"

    xmlns:vm="using:ReactiveUIDemo.ViewModels"

    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">

    <StackPanel x:Name="Panel">

        <Button x:Name="Button">crash</Button>

        <Button x:Name="Button2">crash2</Button>

    </StackPanel>

</Window>

In your repro it doesn't involve with TCC, so this is a bug from Grid not TCC right?

[deryaza]

@laolarou726 it is, but the flow is kind of weird so I can only imagine it in TransitioningContentControl. Maybe it is part of bigger problem like "is it a correct assumption that MeasureOverride always follows by ArrangeOverride and ArrangeOverride always preceeds MeasureOverride (which brings problems in this example)" but idk, not really into inners of avalonia itself.

[electro-logic]

We hit this class of crash in production on 12.1.1 and can answer the open question above concretely: arrange without a preceding measure is reachable from ordinary user code plus a window resize — no InvalidateArrange call involved. The arming sequence is deterministic:

1. A Grid that has no row/column definitions gets measured — MeasureOverride takes the _extData == null simple path, so the definition caches are never populated.
2. User code then calls grid.RowDefinitions.Clear() (a natural "reset the table" idiom when the row source is empty). The property getter lazily creates _extData, and AvaloniaList<T>.Clear() on an already-empty list is guarded by if (Count > 0) — it raises no CollectionChanged, so nothing calls InvalidateMeasure.
3. The grid is now measure-valid with _extData != null but _extData.DefinitionsU/V still null (only MeasureOverride's ValidateDefinitionsUStructure/ValidateDefinitionsVStructure populate them).
4. Any later arrange with changed bounds enters the _extData != null branch of ArrangeOverride and throws NRE at the first DefinitionsV.Count. A window resize is exactly such an arrange: under a ScrollViewer the grid's measure constraint is (Infinity, Infinity) and never changes, so resizes re-arrange it without ever re-measuring — the state never heals.

In an app this looks like: a panel builds its Grid empty, the first data tick finds no rows and calls RowDefinitions.Clear(), and the next window resize kills the process. Reproduced on both the X11 and the native Wayland backend (Wayland trips it spontaneously because compositor configure batches run a synchronous layout pass via HandleResized; X11 needs a manual resize in the armed state).

Two fix directions that would close this particular path, in case they help:

• have the RowDefinitions/ColumnDefinitions getters call InvalidateMeasure() when they lazily create _extData on a grid that has already been measured; or
• have ArrangeOverride detect _extData.DefinitionsU/V == null (created-but-never-measured) and fall back to the simple path / trigger a measure instead of dereferencing.

Workaround for anyone else hitting it: never let a Grid be measured while definition-less and then touch its definition collections without actually changing them — e.g. build columns/header before first layout and grow/shrink rows incrementally instead of Clear()-and-rebuild.