C#•16mo ago

✅ WPF thinks my collection has no items

It's a bit much to explain with full context, but the gist is: An Action has a Fields which has a list of Field.

public partial class ActionViewModel : ViewModelBase
{
    [ObservableProperty] private FieldsViewModel _fields1;

    public ActionViewModel(FxrModel.Action action)
    {
        _fields1 = new FieldsViewModel(action.Fields1);

public partial class ActionViewModel : ViewModelBase
{
    [ObservableProperty] private FieldsViewModel _fields1;

    public ActionViewModel(FxrModel.Action action)
    {
        _fields1 = new FieldsViewModel(action.Fields1);

public partial class FieldsViewModel : ViewModelBase
{
    [ObservableProperty] private ObservableCollection<FieldViewModel> _fields;

    public FieldsViewModel(List<FxrModel.Field> fields)
    {
        _fields = new ObservableCollection<FieldViewModel>();

public partial class FieldsViewModel : ViewModelBase
{
    [ObservableProperty] private ObservableCollection<FieldViewModel> _fields;

    public FieldsViewModel(List<FxrModel.Field> fields)
    {
        _fields = new ObservableCollection<FieldViewModel>();

public partial class FieldViewModel : ViewModelBase
{
    [ObservableProperty] private FxrModel.Field _field;

    public Fxr3.FieldType Type => _field.Type;

    public object Value
    {
        get => _field.Value;
        set
        {
            OnPropertyChanging();
            _field.Value = value;
            OnPropertyChanged();
        }
    }

    public FieldViewModel(FxrModel.Field field)
    {
        _field = field;
    }
}

public partial class FieldViewModel : ViewModelBase
{
    [ObservableProperty] private FxrModel.Field _field;

    public Fxr3.FieldType Type => _field.Type;

    public object Value
    {
        get => _field.Value;
        set
        {
            OnPropertyChanging();
            _field.Value = value;
            OnPropertyChanged();
        }
    }

    public FieldViewModel(FxrModel.Field field)
    {
        _field = field;
    }
}

Each of the viewmodels is bound to a View. ActionView has:

        <Label Content="{Binding Fields1.Fields.Count}" ContentStringFormat="Fields1: {0}" />
        <local:RawFieldsView DataContext="{Binding Fields1}" />

        <Label Content="{Binding Fields1.Fields.Count}" ContentStringFormat="Fields1: {0}" />
        <local:RawFieldsView DataContext="{Binding Fields1}" />

RawFieldsView has:

    <StackPanel>
        <Label Content="{Binding Fields.Count}" />
        <ItemsControl ItemsSource="{Binding Fields}">
        <ItemsControl.ItemTemplate>
                <DataTemplate>
                    <WrapPanel>
                        <Label HorizontalAlignment="Right" Margin="{adonisUi:Space 0, 1.3, 1, 0}"
                               Content="{Binding Type}" />
                        <TextBox Margin="{adonisUi:Space 0, 1, 0, 0}" Text="{Binding Value }" />
                    </WrapPanel>
                </DataTemplate>
            </ItemsControl.ItemTemplate>
        </ItemsControl>
    </StackPanel>

    <StackPanel>
        <Label Content="{Binding Fields.Count}" />
        <ItemsControl ItemsSource="{Binding Fields}">
        <ItemsControl.ItemTemplate>
                <DataTemplate>
                    <WrapPanel>
                        <Label HorizontalAlignment="Right" Margin="{adonisUi:Space 0, 1.3, 1, 0}"
                               Content="{Binding Type}" />
                        <TextBox Margin="{adonisUi:Space 0, 1, 0, 0}" Text="{Binding Value }" />
                    </WrapPanel>
                </DataTemplate>
            </ItemsControl.ItemTemplate>
        </ItemsControl>
    </StackPanel>

But no matter what, Fields.Count always displays 0, and the ItemsControl is empty. I have confirmed that the underlying ViewModels definitely have filled collections with stuff in them. There are definitely not 0 Fields in the Action. And yet, that's what WPF says! Any clues?

1 Reply

iviOP•16mo ago

Resolved by myself; caused by "intended" behavior. I had this combobox hooked up to replace the existing Action with a brandnew one when changed, but that change event fired immediately, causing them all to be replaced by new empty husks immediately. So all the binding was working fine.

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✅ WPF thinks my collection has no items