Use different template for last item in a WPF itemscontrol

Question

I'm using a custom template in my itemscontrol to display the following result:

item 1, item 2, item3,

I want to change the template of the last item so the result becomes:

item 1, item2, item3

The ItemsControl:

<ItemsControl ItemsSource="{Binding Path=MyCollection}">

    <ItemsControl.ItemsPanel>
        <ItemsPanelTemplate>
            <StackPanel Orientation="Horizontal" IsItemsHost="True"/>
        </ItemsPanelTemplate>
    </ItemsControl.ItemsPanel>

    <ItemsControl.ItemTemplate>
        <DataTemplate>

            <StackPanel Orientation="Horizontal">
                <TextBlock Text="{Binding Path=Name}"/>
                <TextBlock Text=", "/>
            </StackPanel>

        </DataTemplate>
    </ItemsControl.ItemTemplate>

</ItemsControl>

Is there anyone who can give a solution for my problem? Thank you!

Solution 1

I've found the solution for my problem using only XAML. If there is anybody who needs to do the same, use this:

<ItemsControl ItemsSource="{Binding Path=MyCollection}">

    <ItemsControl.ItemsPanel>
        <ItemsPanelTemplate>
            <StackPanel Orientation="Horizontal" IsItemsHost="True"/>
        </ItemsPanelTemplate>
    </ItemsControl.ItemsPanel>

    <ItemsControl.ItemTemplate>
        <DataTemplate>

            <StackPanel Orientation="Horizontal">
                <TextBlock x:Name="comma" Text=", "/>
                <TextBlock Text="{Binding}"/>
            </StackPanel>

            <DataTemplate.Triggers>
                <DataTrigger Binding="{Binding RelativeSource={RelativeSource PreviousData}}" Value="{x:Null}">
                    <Setter TargetName="comma" Property="Visibility" Value="Collapsed"/>
                </DataTrigger>
            </DataTemplate.Triggers>

        </DataTemplate>
    </ItemsControl.ItemTemplate>

</ItemsControl>

Solution 2

You can use DataTemplateSelector, in SelectTemplate() method you can check whether item is the last and then return an other template.

In XAML:

<ItemsControl.ItemTemplate>     
  <DataTemplate>
      <ContentPresenter 
             ContentTemplateSelector = "{StaticResource MyTemplateSelector}">

In Code behind:

 private sealed class MyTemplateSelector: DataTemplateSelector
 { 

    public override DataTemplate SelectTemplate(
                                      object item, 
                                      DependencyObject container)
    {
        // ...
    }
  }

Solution 3

This solution affects the last row and updates with changes to the underlying collection:

---

CodeBehind

The converter requires 3 parameters to function properly - the current item, the itemscontrol, the itemscount, and returns true if current item is also last item:

  class LastItemConverter : IMultiValueConverter
    {

        public object Convert(object[] values, Type targetType, object parameter, CultureInfo culture)
        {
            int count = (int)values[2];

            if (values != null && values.Length == 3 && count>0)
            {
                System.Windows.Controls.ItemsControl itemsControl = values[0] as System.Windows.Controls.ItemsControl;
                var itemContext = (values[1] as System.Windows.Controls.ContentPresenter).DataContext;
            
                var lastItem = itemsControl.Items[count-1];

                return Equals(lastItem, itemContext);
            }

            return DependencyProperty.UnsetValue;
        }

        public object[] ConvertBack(object value, Type[] targetTypes, object parameter, CultureInfo culture)
        {
            throw new NotImplementedException();
        }
    }

---

XAML

The Data-Trigger for a DataTemplate, that includes a textbox named 'PART_TextBox':

  <DataTemplate.Triggers>
            <DataTrigger Value="True" >
                <DataTrigger.Binding>
                    <MultiBinding Converter="{StaticResource LastItemConverter}">
                        <Binding RelativeSource="{RelativeSource FindAncestor, AncestorType={x:Type ItemsControl}}" />
                        <Binding RelativeSource="{RelativeSource Self}"/>
                        <Binding RelativeSource="{RelativeSource FindAncestor, AncestorType={x:Type ItemsControl}}" Path="Items.Count"/>
                    </MultiBinding>
                </DataTrigger.Binding>
                <Setter Property="Foreground" TargetName="PART_TextBox" Value="Red" />
            </DataTrigger>
 </DataTemplate.Triggers>      

The converter as a static resource in the Xaml

<Window.Resources>
     <local:LastItemConverter x:Key="LastItemConverter" />
</Window.Resources>

---

SnapShot

And a snapshot of it in action

The code has been added to the itemscontrol from this 'codeproject' https://www.codeproject.com/Articles/242628/A-Simple-Cross-Button-for-WPF

Note the last item's text in red

Comments

[Bram W.]

With the supplied parameters (item and container), there is no way that I can determine whether the item is the last one in the collection.

[sll]

You can find parent ItemsControl container usign FindParentOfType<TParent> method (google intrawebs) and then use AlternationIndex, see StackOverflow fo the examples

[Sheridan]

+1 Nice simple solution. However it should be noted that if any changes are made to the data bound collection (ordering, filtering, adding, or removing), the 'DataTrigger` will not be triggered again and the DataTemplate will not be updated accordingly.

[jpwkeeper]

As a note to those coming here looking for an answer based on the initial question (and other similar questions that erroneously link here), this is not what you are looking for. This solution changes the FIRST item's template, not the LAST item template.

[EightyOne Unite]

jpwkeeper is quite right but that's a damn sexy solution for my problem!

[Giedrius]

Note though, that PreviousData turned out to be very slow for controls with lots of items, having it on 1000 items is unusable.

[Skully]

An alternative for using PreviousData is shown here: stackoverflow.com/a/34138980/3792603 - This answer uses AlternationIndex