windows phone 8 - LongListSelector different item template for first and last item

Question

Im writing my Windows phone 8 app which uses LongListSelector to display some data.

How to set different item template for first and last item in LongListSelector?

Basically I just want to display same information in every item but use little different item "layout" in last and first item.

Answer 1

You could implement some kind of data template selector to help in determining which template to select based on index. You can start off by creating a reusable abstract TemplateSelector class. I used many of the ideas explained in Implementing Windows Phone 7 DataTemplateSelector and CustomDataTemplateSelector but modified implementation to allow for selecting templates based on index instead.

public abstract class TemplateSelector : ContentControl {
  public abstract DataTemplate SelectTemplate(object item, int index, int totalCount, DependencyObject container);

  protected override void OnContentChanged(object oldContent, object newContent) {
    base.OnContentChanged(oldContent, newContent);

    var parent = GetParentByType<LongListSelector>(this);
    var index = parent.ItemsSource.IndexOf(newContent);
    var totalCount = parent.ItemsSource.Count;

    ContentTemplate = SelectTemplate(newContent, index, totalCount, this);
  }

  private static T GetParentByType<T>(DependencyObject element) where T : FrameworkElement {
    T result = null;
    DependencyObject parent = VisualTreeHelper.GetParent(element);

    while (parent != null) {
      result = parent as T;

      if (result != null) {
        return result;
      }

      parent = VisualTreeHelper.GetParent(parent);
    }

    return null;
  }
}

Once you have that class you can add your own data template selector logic. In your case, could be something like this

public class MyTemplateSelector : TemplateSelector {
  public DataTemplate First { get; set; }
  public DataTemplate Default { get; set; }
  public DataTemplate Last { get; set; }

  public override DataTemplate SelectTemplate(object item, int index, int totalCount, DependencyObject container) {
    if (index == 0)
      return First;
    else if (index == totalCount-1)
      return Last;
    else
      return Default;
  }
}

And finally the Xaml

<phone:PhoneApplicationPage.Resources>
    <DataTemplate x:Key="first">
        <TextBlock Text="{Binding Name}" Foreground="Yellow" />
    </DataTemplate>
    <DataTemplate x:Key="default">
        <TextBlock Text="{Binding Name}" />
    </DataTemplate>
    <DataTemplate x:Key="last">
        <TextBlock Text="{Binding Name}" Foreground="Red" />
    </DataTemplate>

    <DataTemplate x:Key="SelectingTemplate">
        <local:MyTemplateSelector Content="{Binding}"
                                First="{StaticResource first}"
                                Default="{StaticResource default}"
                                Last="{StaticResource last}"
                                HorizontalContentAlignment="Stretch" />
    </DataTemplate>
</phone:PhoneApplicationPage.Resources>

<phone:LongListSelector
            ItemTemplate="{StaticResource SelectingTemplate}"
            ItemsSource="{Binding Data}" />