Avalonia: FindControl returns null for UserControl

[braca]

Hi,

I've updated to the latest CI build that uses XAMLIL.

Now the FindControl if used inside the ctor returns null for UserControl example:

    public ImageColorReplacePage()
    {
        this.InitializeComponent();
        this.Initialized += (s, e) =>
        {
            // FindControl after the Initialization is complete works
            var thisWontBeNull = this.FindControl<KitItemInformationView>("kitView");
        };

        // FindControl within the Constructor won't find anything
        var thisOneWillBeNull = this.FindControl<KitItemInformationView>("kitView");
    }

Repro project: https://github.com/braca/avalonia-findcontrol-bug

[jmacato]

@kekekeks This bug could be similar to what @Kermalis got in https://github.com/AvaloniaUI/Avalonia/issues/2632

[kekekeks]

@grokys Decompiled XAML for https://github.com/braca/avalonia-findcontrol-bug/blob/master/MainWindow.xaml

CompiledAvaloniaXaml.XamlIlContext.Context<MainWindow> context = new CompiledAvaloniaXaml.XamlIlContext.Context<MainWindow>(P_0, new object[1]
{
(object)CompiledAvaloniaXaml.!AvaloniaResources.NamespaceInfo:/MainWindow.xaml.Singleton
}, "avares://AvaloniaFindControl/MainWindow.xaml");
context.RootObject = P_1;
((ISupportInitialize)P_1).BeginInit();
P_1.Title = "AvaloniaFindControl";
Grid grid;
Grid grid2 = grid = new Grid();
((ISupportInitialize)grid2).BeginInit();
P_1.Content = grid2;
Grid grid3 = grid;
TextBlock textBlock;
TextBlock obj = textBlock = new TextBlock();
((ISupportInitialize)obj).BeginInit();
IControl control = obj;
Controls children = grid3.Children;
control = control;
((AvaloniaList<IControl>)children).Add(control);
TextBlock obj2 = textBlock;
((StyledElement)obj2).Name = "textBlock";
object obj3 = obj2;
((ILogical)obj3).FindNameScope()?.Register("textBlock", obj3);
obj2.Text = "Hello text block";
((ISupportInitialize)obj2).EndInit();
SampleUserControl sampleUserControl;
SampleUserControl obj4 = sampleUserControl = new SampleUserControl();
((ISupportInitialize)obj4).BeginInit();
control = obj4;
Controls children2 = grid3.Children;
control = control;
((AvaloniaList<IControl>)children2).Add(control);
SampleUserControl obj5 = sampleUserControl;
((StyledElement)obj5).Name = "sampleUserControl";
obj3 = obj5;
((ILogical)obj3).FindNameScope()?.Register("sampleUserControl", obj3);
((ISupportInitialize)obj5).EndInit();
((ISupportInitialize)grid3).EndInit();
((ISupportInitialize)P_1).EndInit();

As you can see both TextBlock and the user control get their name initialized in the same way:

((StyledElement)obj2).Name = "textBlock";
object obj3 = obj2;
((ILogical)obj3).FindNameScope()?.Register("textBlock", obj3);
((ISupportInitialize)obj2).EndInit();

((StyledElement)obj5).Name = "sampleUserControl";
obj3 = obj5;
((ILogical)obj3).FindNameScope()?.Register("sampleUserControl", obj3);
((ISupportInitialize)obj5).EndInit();

Not sure what is wrong here

[Kermalis]

My constructor is also trying to FindControl() a UserControl. The Avalonia controls (TabControl, Button, TextBox, NumericUpDown) are all working with FindControl() within the same constructor:

        public MainView()
        {
            AvaloniaXamlLoader.Load(this);
            DataContext = this;

            tabs = this.FindControl<TabControl>("Tabs");
            teamBuilder = this.FindControl<TeamBuilderView>("TeamBuilder");
            ip = this.FindControl<TextBox>("IP");
            port = this.FindControl<NumericUpDown>("Port");
            connect = this.FindControl<Button>("Connect");
            connect.Command = ReactiveCommand.Create(Connect);
            teamBuilder.Load(); // Crash here because teamBuilder is null (It inherits UserControl)
        }

This happens in every constructor of mine that tries to FindControl() a UserControl, not just this specific one. Below is an example where I have the view constructed within my code [var bv = new BattleView(client);]

        public BattleView()
        {
            // This constructor only exists so xaml compiles, I did not need it for stable 0.8.0
            AvaloniaXamlLoader.Load(this);
        }
        public BattleView(BattleClient client)
        {
            AvaloniaXamlLoader.Load(this);
            Client = client;
            Client.BattleView = this;
            Field = this.FindControl<FieldView>("Field");
            Field.SetBattleView(this); // Crash here because Field is null (It inherits UserControl)
            Actions = this.FindControl<ActionsView>("Actions");
            Actions.BattleView = this;
            messages = this.FindControl<MessageView>("Messages");
        }

All of these examples were working in 0.8.0.

[Kermalis]

The Initialized workaround no longer works, as the FindControl() will return null in there now as well. It is now impossible to get the UserControls.

[kekekeks]

XamlIl might be registering the user control in its own name scope, which might be the issue here.

[Kermalis]

For anyone who wants a workaround, here's a method you can use:

        private void Find()
        {
            //var thing = this.FindControl<MyUserControl>("TheName");
            var thing = this.TemporaryFix<MyUserControl>("TheName");
        }

        // Temporary fix for https://github.com/AvaloniaUI/Avalonia/issues/2562
        private T TemporaryFix<T>(string name) where T : UserControl
        {
            T Recursion(System.Collections.Generic.IEnumerable<Avalonia.LogicalTree.ILogical> list)
            {
                foreach (Avalonia.LogicalTree.ILogical i in list)
                {
                    if (i is Avalonia.INamed named && named is T ret && ret.Name == name)
                    {
                        return ret;
                    }
                    else
                    {
                        T r = Recursion(i.LogicalChildren);
                        if (r != null)
                        {
                            return r;
                        }
                    }
                }
                return null;
            }
            return Recursion(this.LogicalChildren);
        }

You would put TemporaryFix() in your class since this.LogicalChildren is actually protected for UserControls. You could put it in some utils class if you pass this.LogicalChildren as another parameter instead.

[kekekeks]

Should be fixed by https://github.com/AvaloniaUI/Avalonia/pull/2705