DataGrid.ColumnWidth=“*” not working in a ScrollViewer

Question

I have a DataGrid with ColumnWidth="*" in a ScrollViewer with HorizontalScrollBarVisibility="Auto" . Unfortunately this combination doesn't seem to work well. While the DataGrid spans properly over the full window width the columns are super small ( MinWidth ). If I change HorizontalScrollBarVisibility to Disabled it works but I lose the desired ScrollViewer behavior.

Minimal Working Example:

<Window x:Class="WPF_Sandbox.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:local="clr-namespace:WPF_Sandbox"
        Title="MainWindow"
        x:Name="ThisControl">
    <ScrollViewer HorizontalScrollBarVisibility="Auto">
        <DataGrid AutoGenerateColumns="False" ColumnWidth="*">
            <DataGrid.Columns>
                <DataGridTextColumn Header="Column 1" />
                <DataGridTextColumn Header="Column 2" />
                <DataGridTextColumn Header="Column 3" />
                <DataGridTextColumn Header="Column 4" />
            </DataGrid.Columns>
        </DataGrid>
    </ScrollViewer>
</Window>

Why is this happening and how can I work around it?

Answer 1

The problem you see is because as the Datagrid is inside a ScrollViewer, it has virtually infinite space to expand,so it can't calculate widths. For this to work you can bind the DataGrid Width to the ScrollViewer ViewportWidth, as this:

<DataGrid AutoGenerateColumns="False" ColumnWidth="*" 
Width="{Binding RelativeSource={RelativeSource FindAncestor, 
AncestorType={x:Type ScrollViewer}}, Path=ViewportWidth}">