触发自动生成的DataGrid列

Question

I currently work on a WPF project which handels data within an auto-generated data grid. How can I set up a trigger, for changing the background color of a column depending on an empty textbox?

My current usercontrol XAML creates a grid which keeps and data grid inside. For each DataGridColumnHeader I set a new ContentTemplate, which keeps a TextBlock (for the actual header) and a TextBox for filtering.

I tried to set up a trigger for DataGridCell, which worked, but only changes the color of the cell. I can't find a specific target type for a data grid column.

<UserControl x:Class="...">
<Grid>
    <DataGrid AutoGenerateColums="True" IsReadOnly="True" x:Name="MyDataGrid">
        <DataGrid.Resources>
            <Style TargetType="x:Type DataGridColumnHeader=">
                <Setter Property="ContentTemplate">
                    <Setter.Value>
                        <DataTemplate>
                            <StackPanel>
                                <TextBlock x:Name="myBlock" Text="{Binding}" TextWrapping="Wrap" />
                                <TextBox x:Name="myBox" KeyUp="KeyUpEvent" />
                            </StackPanel>
                        </DataTemplate>
                    </Setter.Value>
                </Setter>
            </Style>
        </DataGrid.Resources>
    </DataGrid>
</Grid>

I expect to change the color of a data grid column, if the TextBox is filled with content. Currently I do not know how to set a specific trigger for a data grid column, if the column are auto-generated. EDIT #1: Something like that:

This is when the data grid doesn't have any filters set. But the appearance changes, as soon as you enter a filter text inside one of the filters, like that:

EDIT #2:

I was able to build a solution for coloring the rows programmatically, without coloring the header. That's missing. Do you have any suggestions?

See the following code:

private void StyleRows(string text, string name)
{
    if(text != "" && column != "")
    {
        foreach(DataGridColumn column in DataGrid.Columns)
        {
            if(column.Header == column)
            {
                Style style = new Style(typeof(DataGridCell));
                style.Settes.Add(new Setter(DataGridCell.BackgroundProperty, System.Windows.Media.Brushes.Red));
                column.cellStyle = style
            }
        }
    }
}

Question: Is there a way to do that inside the XAML?

Thank you for your help!

Answer 1

There is no way to do it in XAML only .

You could try to adjust a ViewModel to provide for each column whether the content of TextBox is empty or not(bind the TextBox.Text to the properties and provide bool properties to check string is null or empty). But it's also not a "XAML only" solution.

If yoy set the CellStyle you will need to observe the control from template and use trigger, but you have no access to it.

I would do it with a Behavior . Once you have written a Behavior you can easily use/reuse it in XAML only without need to touch/adjust a code behind.

public class ObserveEmpty : Behavior<TextBox>
{
    public Control TargetControl
    {
        get { return (Control)GetValue(TargetControlProperty); }
        set { SetValue(TargetControlProperty, value); }
    }
    public static readonly DependencyProperty TargetControlProperty =
        DependencyProperty.Register(nameof(TargetControl), typeof(object), typeof(ObserveEmpty), new PropertyMetadata(null, TargetCtlChanged));

    private static void TargetCtlChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
    {
        (d as ObserveEmpty)?.SetTargetBackground();
    }
    public Brush TargetBgrndBrushOnEmpty { get; set; }
    public Brush TargetBgrndBrush { get; set; }


    protected override void OnAttached()
    {
        base.OnAttached();
        SetTargetBackground();
        AssociatedObject.TextChanged += AssociatedObject_TextChanged;
    }
    protected override void OnDetaching()
    {
        base.OnDetaching();
        AssociatedObject.TextChanged -= AssociatedObject_TextChanged;
    }
    private void AssociatedObject_TextChanged(object sender, TextChangedEventArgs e)
    {
        SetTargetBackground();
    }
    private void SetTargetBackground()
    {
        if (TargetControl != null)
        {
            var brush = string.IsNullOrEmpty(AssociatedObject?.Text) ? TargetBgrndBrushOnEmpty : TargetBgrndBrush;

            TargetControl.Background = brush;

            var dgrClmnHdr = TargetControl as DataGridColumnHeader;
            if (dgrClmnHdr?.Column != null)
            {
                Style style = new Style(typeof(DataGridCell));
                style.Setters.Add(new Setter(DataGridCell.BackgroundProperty, brush));
                dgrClmnHdr.Column.CellStyle = style;
            }
        }
    }
}

xmlns:i="clr-namespace:System.Windows.Interactivity;assembly=System.Windows.Interactivity"
    <DataGrid.Resources>
        <Style TargetType="{x:Type DataGridColumnHeader}">
            <Setter Property="ContentTemplate">
                <Setter.Value>
                    <DataTemplate>
                        <StackPanel>
                            <TextBlock x:Name="myBlock" Text="{Binding}" TextWrapping="Wrap" />
                            <TextBox x:Name="myBox">
                                <i:Interaction.Behaviors>
                                    <local:ObserveEmpty TargetBgrndBrush="Aqua" TargetBgrndBrushOnEmpty="Red" 
                                                        TargetControl="{Binding RelativeSource={RelativeSource AncestorType=DataGridColumnHeader}, Mode=OneWay}"/>
                                </i:Interaction.Behaviors>
                            </TextBox>
                        </StackPanel>
                    </DataTemplate>
                </Setter.Value>
            </Setter>
        </Style>
    </DataGrid.Resources>