Question

I have a ListView in WPF set to GridView, and it has a context menu. How do I only enable the context menu when there is something selected in the ListView?

I want to do all this in XAML to follow the MVVM pattern, so any help would be good.

Answer 1

You should use Triggers. Define the ContextMenu as a resource first.
Here is a short sample:

<Window x:Class="SO.MainWindow"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    Title="MainWindow" Height="350" Width="525">

    <Window.Resources>
        <ContextMenu x:Key="ctxmnu">
            <MenuItem Header="Open" />
            <MenuItem Header="Close" />
        </ContextMenu>
    </Window.Resources>

    <StackPanel>
        <ListView x:Name="lv">
            <ListView.Items>
                <clr:String>Item 1</clr:String>
                <clr:String>Item 2</clr:String>
            </ListView.Items>
            <ListView.View>
                <GridView>
                    <GridViewColumn>
                        <GridViewColumn.CellTemplate>
                            <DataTemplate>
                                <TextBlock Text="{Binding}" />
                            </DataTemplate>
                        </GridViewColumn.CellTemplate>
                    </GridViewColumn>
                </GridView>
            </ListView.View>
            <ListView.Style>
                <Style TargetType="ListView">
                    <Setter Property="ContextMenu" Value="{StaticResource ctxmnu1}" />
                    <Style.Triggers>
                        <Trigger Property="SelectedIndex" Value="-1">
                            <Setter Property="ContextMenu" Value="{x:Null}" />
                        </Trigger>
                    </Style.Triggers>
                </Style>
            </ListView.Style>
        </ListView>
    </StackPanel>
</Window>

Saying all that, I cannot imagine a real scenario when this is what you want to do. First, right clicking on the ListView (to popup the context menu) will select an item. Second – I think this is a bad UI design. It would be better to show the same menu, but disable the items (all the items in your case). This way, it gives the user an indication that a popup menu exists, but its functionality isn’t enabled right now.