How to align items in Non Uniform Layout in WinUI3

Question

How to align items using ItemRepeater in a non uniform layout in Winui3.

Here i need some of my tile to take 2 times the width

Answer 1

Not sure if it is what you want to get, but you can change width in ElementPrepared

A test by changing width from 100 to 200 for items 2 and 6 in 10 items :

    <Grid Background="{ThemeResource ApplicationPageBackgroundThemeBrush}">
        <Grid.RowDefinitions>
            <RowDefinition Height="50"></RowDefinition>
            <RowDefinition Height="*"></RowDefinition>
            <RowDefinition Height="Auto"></RowDefinition>
        </Grid.RowDefinitions>

        <Button x:Name="myButton" Grid.Row="0" Click="MyButton_Click">Click Me</Button>

        <ScrollViewer Grid.Row="1" HorizontalScrollBarVisibility="Disabled" VerticalScrollBarVisibility="Auto">
            <ItemsRepeater x:Name="ir1" ItemsSource="{x:Bind MyItems}">
                <ItemsRepeater.Layout>
                    <LinedFlowLayout/>
                </ItemsRepeater.Layout>

                <ItemsRepeater.ItemTemplate>
                    <DataTemplate x:DataType="x:String">
                        <Border x:Name="ItemBorder"
                            Width="100"
                            Height="100"
                            Margin="5"
                            Background="Blue"/>
                    </DataTemplate>
                </ItemsRepeater.ItemTemplate>
            </ItemsRepeater>
        </ScrollViewer>
    </Grid>

   public ObservableCollection<string> MyItems { get; } = new();

  private async void MyButton_Click(object sender, RoutedEventArgs e)
  {      
      {
          for (int i = 0; i < 10; i++)
          {
              MyItems.Add($"Item {i}");
          }

          ir1.ElementPrepared += ir1_ElementPrepared;
          return;
      }
  }
  
  private void ir1_ElementPrepared(ItemsRepeater sender, ItemsRepeaterElementPreparedEventArgs args)
  {
      int nIndex = sender.GetElementIndex(args.Element);
      if (args.Element is FrameworkElement element)
      {
          if (element.FindName("ItemBorder") is Border border)
          {
              Test items 2 and 6 with Width = 200 and in Red
              if (nIndex == 2 || nIndex == 6)
              {
                  border.Width = 200;
                  border.Background = new SolidColorBrush(Microsoft.UI.Colors.Red);
              }
              else
              {
                  border.Width = 100;
                  border.Background = new SolidColorBrush(Microsoft.UI.Colors.Blue);
               }
          }
      }
  }