ContentControl中的WPF DependencyProperty不绑定TwoWay

Question

I have custom ContentControl

public class FilteringColumnHeader : ContentControl
{
    public static readonly DependencyProperty TextFieldProperty =
        DependencyProperty.Register("TextField", typeof(string), typeof(FilteringColumnHeader), new FrameworkPropertyMetadata(null, FrameworkPropertyMetadataOptions.BindsTwoWayByDefault));

    public string TextField
    {
        get
        {
            return (string)GetValue(TextFieldProperty);
        }
        set { SetValue(TextFieldProperty, value); }
    }
}

With this template style

<Style TargetType="{x:Type c:FilteringColumnHeader}">
    <Setter Property="Template">
        <Setter.Value>
            <ControlTemplate TargetType="{x:Type c:FilteringColumnHeader}">
                <DockPanel>
                    <ContentPresenter DockPanel.Dock="Top" Content="{TemplateBinding Content}" />
                    <TextBox Text="{TemplateBinding TextField}"/>
                </DockPanel>
            </ControlTemplate>
        </Setter.Value>
    </Setter>
</Style>

And this is how I use it in DataGrid in XAML

<DataGridTextColumn x:Name="NameColumn" Header="Name" Binding="{Binding Name}" Width="*" MinWidth="50">
    <DataGridTextColumn.HeaderTemplate>
        <DataTemplate>
            <c:FilteringColumnHeader Content="{Binding }" Width="{Binding ActualWidth, ElementName=NameColumn}" TextField="{Binding DataContext.NameFilter, RelativeSource={RelativeSource AncestorType={x:Type local:GeneratorsListView}}, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}"/>
        </DataTemplate>
    </DataGridTextColumn.HeaderTemplate>
</DataGridTextColumn>

And GeneratorsListView

private string nameFilter = "rec";
public string NameFilter
{
    get { return nameFilter; }
    set
    {
        nameFilter = value;
    }
}

My problem is, the Text binding works only OneWay. When I run the code TextBox will be filled with "rec" and when I change the NameFilter , the TextBox also changes. But when I type something in that box, nothing happens (setter of NameFilter is not being invoked at all). As you can see I've tried to set mode to TwoWay everywhere I could, still nothing. When I pleace regular TextBox inside DataTemplate and set the exact same Text binding, it is working.

Answer 1

{TemplateBinding} is an optimized version of a binding with a mode of OneWay so if you want the property to get updated you should use an ordinary binding with the RelativeSource set to TemplatedParent :

<ControlTemplate TargetType="{x:Type c:FilteringColumnHeader}">
    <DockPanel>
        <ContentPresenter DockPanel.Dock="Top" Content="{TemplateBinding Content}" />
        <TextBox Text="{Binding TextField, UpdateSourceTrigger=PropertyChanged, RelativeSource={RelativeSource TemplatedParent}}"/>
    </DockPanel>
</ControlTemplate>