How to enable a button when a treeview-item has selected?

I have a treeview and a button.

I want to disable the button (IsEnabled=false) when there is NO item selected in the treeview (and I want to enable the button when there is an 开发者_高级运维item selected...).

How can I do this?

Here is my XAML:

  <Window
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:i="http://schemas.microsoft.com/expression/2010/interactivity" xmlns:ei="http://schemas.microsoft.com/expression/2010/interactions"
    x:Class="WpfApplicationTreeViewTest.MainWindow"
    x:Name="Window"
    Title="MainWindow"
    Width="640" Height="480" WindowStartupLocation="CenterScreen" Margin="40" >
    <StackPanel> 
        <TreeView x:Name="strategyTreeView" Margin="10 40 10 10">       
            <TreeViewItem Header="Test"></TreeViewItem> 
            <TreeViewItem Header="Test"></TreeViewItem> 
            <TreeViewItem Header="Test"></TreeViewItem> 
            <TreeViewItem Header="Test"></TreeViewItem> 
        </TreeView>     
        <Button Name="Panel" Content="Selected" Height="40" Width="100" Margin="10"/>   
    </StackPanel>       
</Window>

---

You can achieve this with a trigger on the button like this:

<StackPanel>
    <TreeView x:Name="strategyTreeView" Margin="10 40 10 10">
        <TreeViewItem Header="Test"></TreeViewItem>
        <TreeViewItem Header="Test"></TreeViewItem>
        <TreeViewItem Header="Test"></TreeViewItem>
        <TreeViewItem Header="Test"></TreeViewItem>
    </TreeView>
    <Button Name="Panel" Content="Selected" Height="40" Width="100" Margin="10">
        <Button.Style>
            <Style TargetType="{x:Type Button}">
                <Style.Triggers>
                    <DataTrigger Binding="{Binding ElementName=strategyTreeView, Path=SelectedItem}" Value="{x:Null}">
                        <Setter Property="IsEnabled" Value="False"/>
                    </DataTrigger>
                </Style.Triggers>
            </Style>
        </Button.Style>
    </Button>
</StackPanel>

---

Initially you have to disable the Button as after being loaded, the control will have no selection, by using this XAML...

<Button Name="Panel" Content="Selected" Height="40" Width="100" Margin="10" IsEnabled="False"/>

After this you can handle the SelectedItemChanged of the TreeView and enable or disable the button from the method, like this: XAML:

<TreeView x:Name="strategyTreeView" Margin="10 40 10 10" SelectedItemChanged="strategyTreeView_SelectedItemChanged">

Code behind:

private void strategyTreeView_SelectedItemChanged(object sender, RoutedPropertyChangedEventArgs<object> e)
{
    if (e.NewValue != null)
        Panel.IsEnabled = true;
}