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How to dynamically change panel of ItemsControl?
Let's say I have some collection of data. My goal is to provide different kind of view of ItemsControl
depending on user`s preference.
For simplicity, we can assume that user can select only between two states - horizontal & vertical.
MCVE
public enum ViewType { H, V }
public class MainWindowViewModel : ViewModelBase
{
private ViewType _viewType;
public MainWindowViewModel()
{
Values = Enumerable.Range(0, 20).Select(v => v.ToString());
ViewTypes = new[] { ViewType.H, ViewType.V };
ViewType = ViewTypes[0];
}
public ViewType ViewType
{
get => _viewType;
set => this.RaiseAndSetIfChanged(ref _viewType, value);
}
public IEnumerable<string> Values { get; }
public ViewType[] ViewTypes { get; }
}
<Grid RowDefinitions="*,Auto">
<ItemsControl Items="{Binding Values}"
Grid.Row="0" />
<ComboBox Items="{Binding ViewTypes}"
Grid.Row="1"
SelectedItem="{Binding ViewType}"/>
</Grid>
But I wasn't able to find a way to define selector for ItemsPanelTemplate
.
When I tried to use converter:
ItemsPanel="{Binding ViewType, Converter={StaticResource ResourceKey=converter}}"
public class ViewTypePanelConverter : IValueConverter
{
public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
{
var template = new ItemsPanelTemplate()
{
Content = new Func<IServiceProvider, ControlTemplateResult>( _ => {
var content =
value switch
{
ViewType.V => new StackPanel { Orientation = Orientation.Vertical },
ViewType.H => new StackPanel { Orientation = Orientation.Horizontal },
_ => throw new NotImplementedException(),
};
return new ControlTemplateResult(content, new NameScope());
})
};
return template;
}
public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
{
throw new NotImplementedException();
}
}
it has zero effect.
This Q is inspired by Use DataTemplate for ItemsControl.ItemsPanel
#7268 discussion from Avalonia
project repo.
1 answer
This isn't the cleanest approach but at least it works.
One can define two different templates (each of them contains ItemsControl
with single difference in ItemsPanelTemplate
) and switch between them as needed with a simple "selector":
C#:
public class ViewTypeTemplateSelector : IDataTemplate
{
[Content]
public Dictionary<ViewType, IDataTemplate> Templates { get; }
= new Dictionary<ViewType, IDataTemplate>();
public IControl Build(object data) => Templates[(ViewType)data].Build(data);
public bool Match(object data) => data is ViewType;
}
xaml:
<ContentControl Grid.Row="0" Content="{Binding ViewType}">
<ContentControl.Resources>
<DataTemplate x:Key="itemTemplate">
<TextBlock Text="{Binding}" Margin="2" Padding="2"/>
</DataTemplate>
</ContentControl.Resources>
<ContentControl.DataTemplates>
<views:ViewTypeTemplateSelector>
<DataTemplate x:Key="H">
<ItemsControl ItemTemplate="{StaticResource ResourceKey=itemTemplate}" Items="{Binding Values}" DataContext="{Binding $parent[Window].DataContext}">
<ItemsControl.ItemsPanel>
<ItemsPanelTemplate>
<StackPanel Orientation="Horizontal"/>
</ItemsPanelTemplate>
</ItemsControl.ItemsPanel>
</ItemsControl>
</DataTemplate>
<DataTemplate x:Key="V">
<ItemsControl ItemTemplate="{StaticResource ResourceKey=itemTemplate}" Items="{Binding Values}" DataContext="{Binding $parent[Window].DataContext}">
<ItemsControl.ItemsPanel>
<ItemsPanelTemplate>
<StackPanel Orientation="Vertical"/>
</ItemsPanelTemplate>
</ItemsControl.ItemsPanel>
</ItemsControl>
</DataTemplate>
</views:ViewTypeTemplateSelector>
</ContentControl.DataTemplates>
</ContentControl>
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