DataGrid数据源和滚动条在同时使用时有崩溃风险

[SagapoSheepL]

Describe the bug

构建一个DataGrid并且使用根据数据源自动生成数据的功能，然后频繁更新数据源，同时频繁拖动滚动条，DataGrid.ComputeDisplayedColumns方法会提示引用空对象的错误。应该是多线程处理了Column对象导致的。

To Reproduce

构建一个DataGrid，将它的AutoGenerateColumns属性打开，并且创建后台ViewModel对象绑定一个数组类型数据源，接下来构建一个线程为数据生成新的数组数据，打开界面，调整宽度使得表格出现横向的滚动条，然后伴随着数据刷新，左右快速的拖动滚动条，持续大约一分钟，有概率提示错误信息空对象的引用。

Expected behavior

No response

Avalonia version

11.1.0-beta2

OS

Windows, Linux

Additional context

No response

[MikeCodesDotNET]

We kindly request that all issues be reported in English. This helps ensure clear communication and efficient handling of your concerns.

[SagapoSheepL]

We kindly request that all issues be reported in English. This helps ensure clear communication and efficient handling of your concerns.

I'm sorry about that. I encountered some issues while using the DataGrid, I quickly shake its horizontal scrollbar left and right when the data source of the DataGrid is frequently updated, the DataGrid throws an exception and cannot capture it, causing the program to end. I suspect there may be issues with multi-threaded processing but I am not capable of resolving them.

---

 System.NullReferenceException: Object reference not set to an instance of an object.
   at Avalonia.Controls.DataGrid.ComputeDisplayedColumns()
   at Avalonia.Controls.DataGrid.ComputeScrollBarsLayout()
   at Avalonia.Controls.DataGrid.ClearRows(Boolean recycle)
   at Avalonia.Controls.DataGrid.OnItemsSourcePropertyChanged(AvaloniaPropertyChangedEventArgs e)
   at Avalonia.Controls.DataGrid.<>c.<.cctor>b__233_0(DataGrid x, AvaloniaPropertyChangedEventArgs e)
   at Avalonia.AvaloniaObjectExtensions.ClassHandlerObserver`1.OnNext(AvaloniaPropertyChangedEventArgs value)
   at Avalonia.Reactive.LightweightObservableBase`1.PublishNext(T value)
   at Avalonia.Reactive.LightweightSubject`1.OnNext(T value)
   at Avalonia.AvaloniaProperty`1.NotifyChanged(AvaloniaPropertyChangedEventArgs`1 e)
   at Avalonia.AvaloniaObject.RaisePropertyChanged[T](AvaloniaProperty`1 property, Optional`1 oldValue, BindingValue`1 newValue, BindingPriority priority, Boolean isEffectiveValue)
   at Avalonia.PropertyStore.EffectiveValue`1.SetAndRaiseCore(ValueStore owner, StyledProperty`1 property, T value, BindingPriority priority, Boolean isOverriddenCurrentValue, Boolean isCoercedDefaultValue)
   at Avalonia.PropertyStore.EffectiveValue`1.SetLocalValueAndRaise(ValueStore owner, StyledProperty`1 property, T value)
   at Avalonia.PropertyStore.EffectiveValue`1.SetLocalValueAndRaise(ValueStore owner, AvaloniaProperty property, Object value)
   at Avalonia.PropertyStore.ValueStore.SetLocalValue(AvaloniaProperty property, Object value)
   at Avalonia.PropertyStore.ValueStore.Avalonia.Data.Core.IBindingExpressionSink.OnChanged(UntypedBindingExpressionBase instance, Boolean hasValueChanged, Boolean hasErrorChanged, Object value, BindingError error)
   at Avalonia.Data.Core.UntypedBindingExpressionBase.PublishValue(Object value, BindingError error)
   at Avalonia.Data.Core.BindingExpression.ConvertAndPublishValue(Object value, BindingError error)
   at Avalonia.Data.Core.BindingExpression.OnNodeError(Int32 nodeIndex, String error)
   at Avalonia.Data.Core.ExpressionNodes.ExpressionNode.SetError(String message)
   at Avalonia.Data.Core.ExpressionNodes.ExpressionNode.SetError(Exception e)
   at Avalonia.Data.Core.ExpressionNodes.ExpressionNode.SetValue(Object valueOrNotification)
   at Avalonia.Data.Core.ExpressionNodes.PropertyAccessorNode.OnValueChanged(Object newValue)
   at Avalonia.Data.Core.Plugins.PropertyAccessorBase.PublishValue(Object value)
   at Avalonia.Markup.Xaml.MarkupExtensions.CompiledBindings.InpcPropertyAccessor.SendCurrentValue()
   at Avalonia.Markup.Xaml.MarkupExtensions.CompiledBindings.InpcPropertyAccessor.OnEvent(Object sender, WeakEvent ev, PropertyChangedEventArgs e)
  at Avalonia.Utilities.WeakEvent`2.Subscription.OnEvent(Object sender, TEventArgs eventArgs)
   at Avalonia.Utilities.WeakEvents.<>c__DisplayClass5_2.<.cctor>b__9()
   at Avalonia.Threading.DispatcherOperation.InvokeCore()
   at Avalonia.Threading.DispatcherOperation.Execute()
   at Avalonia.Threading.Dispatcher.ExecuteJob(DispatcherOperation job)
   at Avalonia.Threading.Dispatcher.ExecuteJobsCore(Boolean fromExplicitBackgroundProcessingCallback)
   at Avalonia.Threading.Dispatcher.Signaled()
   at Avalonia.Win32.Win32DispatcherImpl.DispatchWorkItem()
   at Avalonia.Win32.Win32Platform.WndProc(IntPtr hWnd, UInt32 msg, IntPtr wParam, IntPtr lParam)
   at Avalonia.Win32.Interop.UnmanagedMethods.DispatchMessage(MSG& lpmsg)
   at Avalonia.Win32.Win32DispatcherImpl.RunLoop(CancellationToken cancellationToken)
   at Avalonia.Threading.DispatcherFrame.Run(IControlledDispatcherImpl impl)
   at Avalonia.Threading.Dispatcher.PushFrame(DispatcherFrame frame)
   at Avalonia.Threading.Dispatcher.MainLoop(CancellationToken cancellationToken)
   at Avalonia.Controls.ApplicationLifetimes.ClassicDesktopStyleApplicationLifetime.Start(String[] args)
   at Avalonia.ClassicDesktopStyleApplicationLifetimeExtensions.StartWithClassicDesktopLifetime(AppBuilder builder, String[] args, Action`1 lifetimeBuilder)

    public partial class MainWindowViewModel : ObservableObject
    {
        [ObservableProperty]
        private CodeList[] _dataSource = Array.Empty<CodeList>();

        public MainWindowViewModel()
        {
            Task.Run(async () =>
            {
                while (true)
                {
                    var len = Random.Shared.Next(20, 100);
                    var test = new CodeList[len];
                    for (var i = 0; i < len; i++)
                    {
                        test[i] = new CodeList()
                        {
                            Code1 = Random.Shared.Next(int.MinValue, int.MaxValue).ToString("D22"),
                            Code2 = Random.Shared.Next(int.MinValue, int.MaxValue).ToString("D22"),
                            Code3 = Random.Shared.Next(int.MinValue, int.MaxValue).ToString("D22"),
                            Code4 = Random.Shared.Next(int.MinValue, int.MaxValue).ToString("D22"),
                            Code5 = Random.Shared.Next(int.MinValue, int.MaxValue).ToString("D22"),
                            Code6 = Random.Shared.Next(int.MinValue, int.MaxValue).ToString("D22"),
                            Code7 = Random.Shared.Next(int.MinValue, int.MaxValue).ToString("D22"),
                            Code8 = Random.Shared.Next(int.MinValue, int.MaxValue).ToString("D22")
                        };
                    }
                    DataSource = test;
                    await Task.Delay(1000);
                }
            });
        }
    }

    public class CodeList
    {
        public string Code1 { get; set; } = string.Empty;
        public string Code2 { get; set; } = string.Empty;
        public string Code3 { get; set; } = string.Empty;
        public string Code4 { get; set; } = string.Empty;
        public string Code5 { get; set; } = string.Empty;
        public string Code6 { get; set; } = string.Empty;
        public string Code7 { get; set; } = string.Empty;
        public string Code8 { get; set; } = string.Empty;
    }

	<DataGrid Margin="5"
			  AutoGenerateColumns="True"
			  ItemsSource="{Binding DataSource}"
			  IsReadOnly="True"
			  RowHeaderWidth="50"
			  Padding="0"
			  FontSize="25"
			  HeadersVisibility="All"
			  SelectionMode="Extended"
			  CanUserResizeColumns="False"
			  CanUserSortColumns="False"/>

[maxkatz6]

@SagapoSheepL any manipulation with UI elements should happen on UI thread.
On line DataSource = test; you change UI-bound property from non-UI thread, which might break the control.

Consider wrapping it into Dispatcher call:
Dispatcher.UIThread.InvokeAsync(() => DataSource = test);

Or reworking how you do threading.

[SagapoSheepL]

Perhaps you can try to reproduce this issue. I can also write the DataSource = test; on another thread because I used the MVVM design pattern, and it still throws exceptions even with UIThread.

[SagapoSheepL]

@maxkatz6 Hello, I have tried updating the DataSource on UIThread, but there are still issues. I think the updating of the DataSource and the triggering of UI updates by the scrollbar are handled on different threads when Avalonia was written. I cannot separate these two logics outside, which means that when the DataSource is updated and the scrollbar is triggered at the same time, the program will definitely crash.

[zhaoyushun1999]

i meet the same question,so,i used a list which made by myself.here you are the code. maybe helpful for you.using AsyncObservableCollection instade of ObservableCollection.
`using System;
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.Collections.Specialized;
using System.ComponentModel;
using System.Linq;
using System.Text;
using System.Threading;
using System.Threading.Tasks;

namespace AvaloniaRiderDemo.Common
{
[Serializable]
public class AsyncObservableCollection:ObservableCollection
{
[NonSerialized]
private SynchronizationContext _synchronizationContext = SynchronizationContext.Current;
public AsyncObservableCollection()
{
if (_synchronizationContext == null)
{
_synchronizationContext = SynchronizationContext.Current;
}
}
public AsyncObservableCollection(IEnumerable list) : base(list) { }
protected override void OnCollectionChanged(NotifyCollectionChangedEventArgs e)
{
if (_synchronizationContext == null)
{
_synchronizationContext = SynchronizationContext.Current;
}
if (SynchronizationContext.Current == _synchronizationContext)
{
RaiseCollectionChanged(e);
}
else
{
_synchronizationContext.Post(RaiseCollectionChanged, e);
}

    }

    private void RaiseCollectionChanged(object param)
    {
        try
        {
            // 执行         
            base.OnCollectionChanged((NotifyCollectionChangedEventArgs)param);
        }
        catch
        { }
    }

    protected override void OnPropertyChanged(PropertyChangedEventArgs e)
    {
        if (_synchronizationContext == null)
        {
            _synchronizationContext = SynchronizationContext.Current;
        }
        if (SynchronizationContext.Current == _synchronizationContext)
        {  
            RaisePropertyChanged(e);
        }

        else
        {     
            _synchronizationContext.Post(RaisePropertyChanged, e);
        }

    }

    private void RaisePropertyChanged(object param)
    {
        base.OnPropertyChanged((PropertyChangedEventArgs)param);
    }

}

}
`

[SagapoSheepL]

This method is very effective, thank you very much. I think the official should modify the source code to support this situation and this exception cannot be catch, that is bad experience.