Question

I am wanting to receive keyboard input from a Popup control that acts as the root visual for a touch screen keyboard control. I’m wanting the control to support keyboard input as well as touch screen input. I hook up the events (PreviewKeyDown and KeyDown) and they are never fired.

Answer 1

A Popup is not focusable by default and even if it is focusable, you have to have something else focusable on the popup and then get it focused or give it the focus in order for it to receive keyboard event.

In other words, if you want keyboard event from the Popup use Focusable="True" and put a focusable control like a TextBox or a Button or a ListBox and either let the user give it the focus by clicking on it or manually use Focus() from code. If you do all these things then PreviewKeyDown should fire for the Popup.

Here is a little demonstration program with a toggle button that opens a Popup and that shows a slider increasing whenever we get a PreviewKeyDown event on a Popup:

<Grid>
    <StackPanel>
        <Slider Name="slider1"/>
        <ToggleButton x:Name="toggleButton1" 
                      Content="Open Popup"/>
    </StackPanel>
    <Popup PlacementTarget="{Binding ElementName=toggleButton1}" 
           IsOpen="{Binding IsChecked, ElementName=toggleButton1, Mode=OneWay}" 
           Focusable="True">
        <i:Interaction.Triggers>
            <i:EventTrigger EventName="PreviewKeyDown">
                <ei:ChangePropertyAction TargetObject="{Binding ElementName=slider1}" 
                                         PropertyName="Value" 
                                         Value="1" 
                                         Increment="True"/>
            </i:EventTrigger>
        </i:Interaction.Triggers>
        <TextBox Background="White" 
                 Focusable="True">
            <TextBox.Text>Sample Popup content.</TextBox.Text>
        </TextBox>
    </Popup>
</Grid>