例如

<DataGrid RowDetailsVisibilityMode="Collapsed">
    <DataGrid.RowStyle>
        <Style TargetType="{x:Type DataGridRow}">
            <EventSetter Event="MouseDoubleClick" Handler="RowDoubleClick"/>
        </Style>
    </DataGrid.RowStyle>
</DataGrid>

private void RowDoubleClick(object sender, RoutedEventArgs e)
{
    var row = (DataGridRow)sender;
    row.DetailsVisibility = row.DetailsVisibility == Visibility.Collapsed ?
        Visibility.Visible : Visibility.Collapsed;
}