How to change itemsControl stackpanel background color

Question

Says I have a list of 10 items someList, I will show them on my page via itemsControl like below:

<ItemsControl DataContext="{Binding [someViewModel]}" 
              BorderBrush="Black" 
              ItemSource="{Binding someList}">
    <ItemsControl.ItemTemplate>
        <DataTemplate>
            <Border BorderThickness="1" Background="Green">
                <StackPanel MouseDown="{Binding Path=DataContext.someCommand,   
                                        RelativeSource={RelativeSource FindAncestor,AncestorType={x:Type ItemsControl}}}" 
                                        Command Parameter="{Binding someID}">
                    <TextBlock Text="{Binding something}">
                </StackPanel>
            </Border>
        </DataTemplate>
    </ItemsControl.ItemTemplate>
</ItemsControl>

I do able to trigger someCommand method and I do able to pass in someID as input parameter. Now I'm wondering how to update the stackPanel background color, making it looks like "selected". Meaning now all item will have a green background, when I click on one of the stackpanel, that stackpanel should change background to red and change others back to green

Answer 1

If you want to use ItemsControl you can change ItemTemplate to RadioButton with custom ControlTemplate that will include Border which Background would change to Red when IsChecked == true:

<ItemsControl DataContext="{Binding [someViewModel]}" BorderBrush="Black" ItemSource="{Binding someList}">
    <ItemsControl.ItemTemplate>
        <DataTemplate>
            <RadioButton Content="{Binding something}" GroupName="radioGroup">
                <RadioButton.Template>
                    <ControlTemplate TargetType="{x:Type RadioButton}">
                        <Border Background="Green" x:Name="PART_Border">
                            <ContentPresenter/>
                        </Border>
                        <ControlTemplate.Triggers>
                            <Trigger Property="IsChecked" Value="True">
                                <Setter TargetName="PART_Border" Property="Background" Value="Red"/>
                            </Trigger>
                        </ControlTemplate.Triggers>
                    </ControlTemplate>
                </RadioButton.Template>
            </RadioButton>
        </DataTemplate>
    </ItemsControl.ItemTemplate>
</ItemsControl>

However I don't see a reason why you cannot use ListBox with SelectionMode=Single (default value) and change Template of ListBoxItem:

<ListBox DataContext="{Binding [someViewModel]}" BorderBrush="Black" ItemSource="{Binding someList}">
    <ListBox.ItemContainerStyle>
        <Style TargetType="{x:Type ListBoxItem}">
            <Setter Property="Template">
                <Setter.Value>
                    <ControlTemplate TargetType="{x:Type ListBoxItem}">
                        <Border Background="Green" x:Name="PART_Border">
                            <ContentPresenter/>
                        </Border>
                        <ControlTemplate.Triggers>
                            <Trigger Property="IsSelected" Value="True">
                                <Setter TargetName="PART_Border" Property="Background" Value="Red"/>
                            </Trigger>
                        </ControlTemplate.Triggers>
                    </ControlTemplate>
                </Setter.Value>
            </Setter>
        </Style>
    </ListBox.ItemContainerStyle>
</ListBox>

or even do something like this, without changing Template:

<ListBox DataContext="{Binding [someViewModel]}" BorderBrush="Black" ItemSource="{Binding someList}">
    <ListBox.Resources>
        <SolidColorBrush x:Key="{x:Static SystemColors.HighlightBrushKey}" Color="Red"/>
    </ListBox.Resources>
    <ListBox.ItemContainerStyle>
        <Style TargetType="{x:Type ListBoxItem}">
            <Setter Property="Background" Value="Green"/>
        </Style>
    </ListBox.ItemContainerStyle>
</ListBox>

In WPF it's generally much easier to pick a control that has functionality that you need and style it to look like you want then do this the other way round

Answer 2

why not do something like this

<DataTemplate>
    <Border BorderThickness="1" Background="Green" x:Name="MyBorder">
        <StackPanel MouseDown="{Binding Path=DataContext.someCommand,   
            RelativeSource={RelativeSource FindAncestor,AncestorType={x:Type ItemsControl}}}" 
            Command Parameter="{Binding someID}">
            <TextBlock Text="{Binding something}">
        </StackPanel>
    </Border>
    <DataTemplate.Triggers>
        <DataTrigger Binding="{Binding Path=IsSelected}" Value="true">
                    <Setter TargetName="MyBorder" Property="Background" Value="Black" />
            </DataTrigger>
    </DataTemplate.Triggers>
</DataTemplate>