WPF: How to enable a Command?

I don't know why the Add item in my context menu is only enabled when there is an item selected in the ListView. Does anybody knows why?

Here's my XAML code

    <Window x:Class="Vokabular1.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">
    <Grid>
        <Grid HorizontalAlignment="Stretch" Name="grid" VerticalAlignment="Stretch">
            <Grid.ColumnDefinitions>
                <ColumnDefinition />
                <ColumnDefinition />
            </Grid.ColumnDefinitions>

            <ListView Grid.Column="0" HorizontalAlignment="Stretch" Margin="10,10,10,10" Name="listView" VerticalAlignment="Stretch">
                <ListView.View>
                    <GridView />
                </ListView.View>
                <ListView.CommandBindings>
                    <CommandBinding Command="New" 
                        Executed="CommandBinding_Executed" 
                        CanExecute="CommandBinding_CanExecute" />
                </ListView.CommandBindings>
                <ListView.ContextMenu>
                    <ContextMenu>
                        <MenuItem Name="Add" Header="_Add"    Command="New" />
                        <MenuItem Header="Delete" Command="Delete" IsEnabled="True" />
                    </ContextMenu>
                </ListView.ContextMenu>
                <ListViewItem />  
            </ListView>            
        </Grid>
    </Grid>
</Window>

The methods for the window are:

private void CommandBinding_Executed(object sender, ExecutedRoutedEventArgs e)
{
    MessageBox.Show("ok");
}

priv开发者_运维问答ate void CommandBinding_CanExecute(object sender, CanExecuteRoutedEventArgs e)
{
    e.CanExecute = true;
    e.Handled = true;
}

Focus is required for the CommandBinding.CanExecute to be called. Since selecting an item in the ListView forces the focus to shift to the ListView; the evaluation can occur.

If you were to place listView.Focus(); within your Window constructor you would note that CommandBinding.CanExecute is now called as expected and therefore enabled without an item being contained or selected within the ListView.

Moving the binding to the Window will still require the focus to get set within the Window; either via an explicit call within the constructor or by another means; ex... selecting an item in the ListView or other control within the Window which can receive focus.