UniformGrid does not adjust layout when Columns property changes.

[DanWatkins]

Changes to the Columns property do not appear to trigger a layout recalculation for the UniformGrid.

In the following example, moving the slider changes the SliderValue VM property, but the changes are not reflected in the UniformGrid (the rendered columns are always at the default of 7):

<DockPanel>
    <Slider Name="slider1" DockPanel.Dock="Top" IsSnapToTickEnabled="True" Minimum="1" Maximum="10" Value="{Binding SliderValue}" TickFrequency="1"/>
    <ItemsControl Grid.Row="1" Items="{Binding TestItems}">
        <ItemsControl.ItemTemplate>
            <DataTemplate>
                <Grid Background="LightGray" Margin="5,5,5,0">
                    <TextBlock Text="{Binding .}" HorizontalAlignment="Center" VerticalAlignment="Center"/>
                </Grid>
            </DataTemplate>
        </ItemsControl.ItemTemplate>
        <ItemsControl.ItemsPanel>
            <ItemsPanelTemplate>
                <UniformGrid Columns="{Binding SliderValue}"/>
            </ItemsPanelTemplate>
        </ItemsControl.ItemsPanel>
    </ItemsControl>
</DockPanel>

public class MainWindowViewModel : ViewModelBase
{
    public List<string> TestItems { get; }

    private int _SliderValue = 7;
    public int SliderValue
    {
        get => _SliderValue;
        set => this.RaiseAndSetIfChanged(ref _SliderValue, value);
    }

    public MainWindowViewModel()
    {
        this.TestItems = new List<string>
        {
            "Test Item 1",
            "Test Item 2",
            "Test Item 3",
            "Test Item 4",
            "Test Item 5"
        };
    }
}

[jp2masa]

I guess it's lacking AffectsRenderAffectsMeasures. I'll fix this.

[cbagpipe]

Experiencing this problem too, but with different layout:

public ObservableCollection<ShellPage>? Items { get; set; }

<ItemsControl.ItemsPanel>
   <ItemsPanelTemplate>
      <UniformGrid Rows="1" Columns="{Binding Items, Converter={StaticResource CollectionToItemsCount}}"/>
   </ItemsPanelTemplate>
</ItemsControl.ItemsPanel>

Workaround:

// Fody.PropertyChanged delegate
 public void OnPropertyChanged(string propertyName, object before, object after)
 {
  if (propertyName == nameof(Items))
     {
         if (before != null && before is ObservableCollection<ShellPage> bItems)
             bItems.CollectionChanged -= ItemsChanged;

         if (after != null && after is ObservableCollection<ShellPage> aItems)
             aItems.CollectionChanged += ItemsChanged;
     }

     PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
 }

 private void ItemsChanged(object? sender, NotifyCollectionChangedEventArgs e)
 {
     switch (e.Action)
     {
         case NotifyCollectionChangedAction.Add:
         case NotifyCollectionChangedAction.Remove:
         case NotifyCollectionChangedAction.Reset:
             OnPropertyChanged(nameof(Items));
             break;
         case NotifyCollectionChangedAction.Move:
         case NotifyCollectionChangedAction.Replace:
         default:
             break;
     }
 }