Question

I’m getting the following Binding errors on my code and I don’t know how to troubleshoot them. The bindings were generated by VS. I’ve tried adding presentation.tracesources (which is in the code below) but I get the same output as before.

System.Windows.Data Error: 4 : Cannot find source for binding with reference 'RelativeSource FindAncestor, AncestorType='ClimateSolutions.SuperTB', AncestorLevel='1''. BindingExpression:Path=myName; DataItem=null; target element is 'TextBlock' (Name=''); target property is 'Text' (type 'String')

System.Windows.Data Error: 4 : Cannot find source for binding with reference 'RelativeSource FindAncestor, AncestorType='ClimateSolutions.SuperTB', AncestorLevel='1''. BindingExpression:Path=isRequired; DataItem=null; target element is 'SuperTB' (Name='email'); target property is 'NoTarget' (type 'Object')

Here’s my XAML:

<TextBox x:Class="ClimateSolutions.SuperTB"
         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:d="http://schemas.microsoft.com/expression/blend/2008" 
         mc:Ignorable="d" Height="53" Width="296" FontSize="32"
         xmlns:local="clr-namespace:ClimateSolutions"
xmlns:diagnostics="clr-namespace:System.Diagnostics;assembly=WindowsBase"

         HorizontalAlignment="Left" Name="Blarg">
<TextBox.Style>
    <Style TargetType="TextBox">
        <Style.Triggers>
            <Trigger Property="Text" Value="">
                <Setter Property="Background">
                    <Setter.Value>
                        <VisualBrush Stretch="None">
                            <VisualBrush.Visual>
                                <TextBlock Foreground="Gray" FontSize="24" Text="{Binding RelativeSource={RelativeSource FindAncestor, AncestorType=local:SuperTB, AncestorLevel=1}, Path=myName, diagnostics:PresentationTraceSources.TraceLevel=High}">
                                </TextBlock>
                            </VisualBrush.Visual>
                        </VisualBrush>
                    </Setter.Value>
                </Setter>
            </Trigger>
            <DataTrigger Binding="{Binding Path=isRequired, RelativeSource={RelativeSource FindAncestor, AncestorType=local:SuperTB, AncestorLevel=1}}" Value="False">
                <Setter Property="Text" Value="100" />
            </DataTrigger>
        </Style.Triggers>
    </Style>
</TextBox.Style>

and here’s the CS for SuperTB:

namespace ClimateSolutions
{
    /// <summary>
    /// Interaction logic for SuperTB.xaml
    /// </summary>
    public partial class SuperTB : TextBox, INotifyPropertyChanged
    {
        public event PropertyChangedEventHandler PropertyChanged;

        private void NotifyPropertyChanged(String Property)
        {
            var anEvent = this.PropertyChanged;

            if (anEvent != null)
            {
                anEvent(this, new PropertyChangedEventArgs(Property));
            }
        }

        private String MyName = "Unicorns!";

        private static DependencyProperty myNameProperty = DependencyProperty.Register("myName", typeof(String), typeof(SuperTB));
        public String myName
        {
            get { return MyName; }
            set { MyName = value; NotifyPropertyChanged("myName"); }
        }

        DependencyProperty isRequiredProperty = DependencyProperty.Register("isRequired", typeof(Boolean), typeof(SuperTB));

        public Boolean isRequired
        {
            get { return (Boolean)GetValue(isRequiredProperty); }
            set { SetValue(isRequiredProperty, value); }
        }

        public SuperTB()
        {
            InitializeComponent();
            myName = "Unicorns!";
        }
    }
}

Answer 1

EDIT : I have updated the code according to your comment. To summarize, since this is a custom control, you are less dependant on the MVVM pattern to build your component logic (and thus use code behind in you component) as soon as your componennt itself meets this needs (to be sort, make its properties to be as much bindable as you can). For example, in the updated code, you can now bind the default property, but you can also imagine exposing properties to set the foreground colors used to diaplay control name when there is no value, and so forth.

---

I tried several things with you original code (included solution provided by J cooper) and nothing seemed to work. It seems that there is a lot of issues with your code.

I managed to approach a solution by making your textbox a custom control.

Here is the Generic.xaml (the visual definition of your control) :

<ResourceDictionary
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:local="clr-namespace:Question_6514447">


<Style TargetType="{x:Type local:SuperTB2}">
    <Setter Property="Template">
        <Setter.Value>
            <ControlTemplate TargetType="{x:Type local:SuperTB2}">
                <Border Background="{TemplateBinding Background}"
                        BorderBrush="{TemplateBinding BorderBrush}"
                        BorderThickness="{TemplateBinding BorderThickness}">
                    <TextBox x:Name="PART_Input">
                        <TextBox.Style>
                            <Style TargetType="TextBox">
                                <Style.Triggers>
                                    <DataTrigger Binding="{Binding RelativeSource={RelativeSource TemplatedParent}, Path=IsRequired}" Value="False">
                                        <Setter Property="Text" Value="{Binding RelativeSource={RelativeSource TemplatedParent}, Path=DefaultTextValue}" />
                                    </DataTrigger>
                                </Style.Triggers>
                            </Style>
                        </TextBox.Style>
                    </TextBox>
                </Border>
            </ControlTemplate>
        </Setter.Value>
    </Setter>
</Style>
</ResourceDictionary>

And here is the code behind of the control :

 [TemplatePart(Name = "PART_Input")]
public class SuperTB2 : Control
{
    private TextBox PART_Input;
    static SuperTB2()
    {
        DefaultStyleKeyProperty.OverrideMetadata(typeof(SuperTB2), new FrameworkPropertyMetadata(typeof(SuperTB2)));
    }

    public SuperTB2()
    {
        Loaded += SuperTb2Loaded;
    }
    public override void OnApplyTemplate()
    {
        PART_Input = GetTemplateChild("PART_Input") as TextBox;
        if (PART_Input != null)
        {


            PART_Input.GotFocus += PartInputGotFocus;
            PART_Input.LostFocus += PartInputLostFocus;
        }
    }

    void PartInputLostFocus(object sender, RoutedEventArgs e)
    {
        if (PART_Input.Text == string.Empty)
        {
            PART_Input.Text = Name;
            PART_Input.Foreground = new SolidColorBrush(Colors.Gray);
        }
    }

    void PartInputGotFocus(object sender, RoutedEventArgs e)
    {
        if (PART_Input.Text.Equals(Name))
        {
            PART_Input.Text = string.Empty;
            PART_Input.Foreground = new SolidColorBrush(Colors.Black);

        }
    }

    void SuperTb2Loaded(object sender, RoutedEventArgs e)
    {
        if (PART_Input.Text == string.Empty)
        {
            PART_Input.Text = Name;
            PART_Input.Foreground = new SolidColorBrush(Colors.Gray);
        }
    }

    private static DependencyProperty myNameProperty =
DependencyProperty.Register("MyName", typeof(string), typeof(SuperTB2), new PropertyMetadata("Unicorns !", NameChanged));

    private static void NameChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
    {

    }

    public string MyName
    {
        get { return (string)GetValue(myNameProperty); }
        set { SetValue(myNameProperty, value); }
    }
    DependencyProperty isRequiredProperty =
        DependencyProperty.Register("IsRequired", typeof(bool), typeof(SuperTB2), new PropertyMetadata(false, IsReqChanged));

    private static void IsReqChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
    {

    }

    public bool IsRequired
    {
        get { return (bool)GetValue(isRequiredProperty); }
        set { SetValue(isRequiredProperty, value); }
    }



    public string DefaultTextValue
    {
        get { return (string)GetValue(DefaultTextValueProperty); }
        set { SetValue(DefaultTextValueProperty, value); }
    }

    // Using a DependencyProperty as the backing store for DefaultTextValue.  This enables animation, styling, binding, etc...
    public static readonly DependencyProperty DefaultTextValueProperty =
        DependencyProperty.Register("DefaultTextValue", typeof(string), typeof(SuperTB2), new UIPropertyMetadata("100"));


}

And an example of use of the component :

<Grid>
    <StackPanel>
        <Question_6514447:SuperTB2 x:Name="FirstName" IsRequired="true" DefaultTextValue="200"/>
    </StackPanel>
</Grid>

With this updated code, I think you can acheive almost all the behaviors your needed !

Hope this will help !