The following approach is the same as Helge Klein's, except that the popup closes automatically when you click anywhere outside the Popup (including the ToggleButton itself):
<ToggleButton x:Name="Btn" IsHitTestVisible="{Binding ElementName=Popup, Path=IsOpen, Mode=OneWay, Converter={local:BoolInverter}}">
<TextBlock Text="Click here for popup!"/>
</ToggleButton>
<Popup IsOpen="{Binding IsChecked, ElementName=Btn}" x:Name="Popup" StaysOpen="False">
<Border BorderBrush="Black" BorderThickness="1" Background="LightYellow">
<CheckBox Content="This is a popup"/>
</Border>
</Popup>
"BoolInverter" is used in the IsHitTestVisible binding so that when you click the ToggleButton again, the popup closes:
public class BoolInverter : MarkupExtension, IValueConverter
{
public override object ProvideValue(IServiceProvider serviceProvider)
{
return this;
}
public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
{
if (value is bool)
return !(bool)value;
return value;
}
public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
{
return Convert(value, targetType, parameter, culture);
}
}
...which shows the handy technique of combining IValueConverter and MarkupExtension in one.
I did discover one problem with this technique: WPF is buggy when two popups are on the screen at the same time. Specifically, if your toggle button is on the "overflow popup" in a toolbar, then there will be two popups open after you click it. You may then find that the second popup (your popup) will stay open when you click anywhere else on your window. At that point, closing the popup is difficult. The user cannot click the ToggleButton again to close the popup because IsHitTestVisible is false because the popup is open! In my app I had to use a few hacks to mitigate this problem, such as the following test on the main window, which says (in the voice of Louis Black) "if the popup is open and the user clicks somewhere outside the popup, close the friggin' popup.":
PreviewMouseDown += (s, e) =>
{
if (Popup.IsOpen)
{
Point p = e.GetPosition(Popup.Child);
if (!IsInRange(p.X, 0, ((FrameworkElement)Popup.Child).ActualWidth) ||
!IsInRange(p.Y, 0, ((FrameworkElement)Popup.Child).ActualHeight))
Popup.IsOpen = false;
}
};
// Elsewhere...
public static bool IsInRange(int num, int lo, int hi) =>
num >= lo && num <= hi;
