wpfevent-handlinglistboxscrollviewermousewheel

Child elements of scrollviewer preventing scrolling with mouse wheel?


I'm having a problem getting mouse wheel scrolling to work in the following XAML, which I have simplified for clarity:

<ScrollViewer
HorizontalScrollBarVisibility="Visible"
VerticalScrollBarVisibility="Visible"
CanContentScroll="False"
>
    <Grid
    MouseDown="Editor_MouseDown"
    MouseUp="Editor_MouseUp"
    MouseMove="Editor_MouseMove"
    Focusable="False"
    >
        <Grid.Resources>
            <DataTemplate
            DataType="{x:Type local:DataFieldModel}"
            >
                <Grid
                Margin="0,2,2,2"
                >
                    <TextBox
                    Cursor="IBeam"
                    MouseDown="TextBox_MouseDown"
                    MouseUp="TextBox_MouseUp"
                    MouseMove="TextBox_MouseMove"
                    />
                </Grid>
            </DataTemplate>
        </Grid.Resources>
        <ListBox
        x:Name="DataFieldListBox"
        ItemsSource="{Binding GetDataFields}"
        SelectionMode="Extended"
        Background="Transparent"
        Focusable="False"
        >
            <ListBox.ItemsPanel>
                <ItemsPanelTemplate>
                    <Canvas />
                </ItemsPanelTemplate>
            </ListBox.ItemsPanel>
            <ListBox.ItemContainerStyle>
                <Style
                TargetType="ListBoxItem"
                >
                    <Setter
                    Property="Canvas.Left"
                    Value="{Binding dfX}"
                    />
                    <Setter
                    Property="Canvas.Top"
                    Value="{Binding dfY}"
                    />
                </Style>
            </ListBox.ItemContainerStyle>
        </ListBox>
    </Grid>
</ScrollViewer>

Visually, the result is an area of some known size where DataFields read from a collection can be represented with TextBoxes which have arbitrary position, size, et cetera. In cases where the ListBox's styled "area" is too large to display all at once, horizontal and vertical scrolling is possible, but only with the scroll bars.

For better ergonomics and sanity, mouse wheel scrolling should be possible, and normally ScrollViewer would handle it automatically, but the ListBox appears to be handing those events such that the parent ScrollViewer never sees them. So far I have only been able to get wheel scrolling working be setting IsHitTestVisible=False for either the ListBox or the parent Grid, but of course none of the child element's mouse events work after that.

What can I do to ensure the ScrollViewer sees mouse wheel events while preserving others for child elements?

Edit: I just learned that ListBox has a built-in ScrollViewer which is probably stealing wheel events from the parent ScrollViewer and that specifying a control template can disable it. I'll update this question if that resolves the problem.


Solution

  • Specifying a ControlTemplate for the Listbox which doesn't include a ScrollViewer solves the problem. See this answer and these two MSDN pages for more information:

    ControlTemplate

    ListBox Styles and Templates