How to avoid default text in textbox?

Question

I have a textbox, which uses multi-binding usingStringFormat...as shown below. But it displays the default value as {DependencyProperty.UnsetValue},{DependencyProperty.UnsetValue}

How to avoid this ?

<StackPanel Orientation="Horizontal">
                    <TextBlock Width="70" Text="Name:" Margin="5,2,2,2"></TextBlock>
                    <TextBox Width="160" DataContext="{Binding }" IsReadOnly="True" Margin="2">
                        <TextBox.Text>
                            <MultiBinding StringFormat="{}{0},{1}">
                                <Binding Path="LastName"/>
                                <Binding Path="FirstName"/>
                            </MultiBinding>
                        </TextBox.Text>
                    </TextBox>
</StackPanel>

Please help me.

Answer 1

Something is wrong with the object you are binding to. I just created an application from scratch with a Person class that inherits from DependencyObject. I left the first and last name properties unset and I did not see DependencyProperty.UnsetValue, but rather a blank TextBox with just a comma in it.

(In general, you shouldn't use dependency properties on your business objects anyway. Stick to INotifyPropertyChanged and save yourself a ton of headaches.)

Post the code to your bound object and maybe I can spot the issue.

public class Person : DependencyObject
{

    public static readonly DependencyProperty FirstNameProperty = DependencyProperty.Register("FirstName", typeof(string), typeof(Person), new FrameworkPropertyMetadata());

    public string FirstName {
        get { return (string)GetValue(FirstNameProperty); }
        set { SetValue(FirstNameProperty, value); }
    }

    public static readonly DependencyProperty LastNameProperty = DependencyProperty.Register("LastName", typeof(string), typeof(Person), new FrameworkPropertyMetadata());

    public string LastName {
        get { return (string)GetValue(LastNameProperty); }
        set { SetValue(LastNameProperty, value); }
    }

}

-

<TextBox IsReadOnly="True">
    <TextBox.Text>
        <MultiBinding StringFormat="{}{1}, {0}">
            <Binding Path="FirstName" />
            <Binding Path="LastName" />
        </MultiBinding>
    </TextBox.Text>
</TextBox>

-

public partial class MainWindow : Window
{
    public MainWindow()
    {
        this.InitializeComponent();
    }

    private void Window_Loaded(object sender, System.Windows.RoutedEventArgs e)
    {
        var p = new Person();
        //p.FirstName = "Josh";
        //p.LastName = "Einstein";          
        DataContext = p;
    }
}

Answer 2

just give the fallbackvalue="" and see

<TextBox.Text>
                <MultiBinding StringFormat="{}{0},{1}">
                    <Binding Path="LastName" FallbackValue=""/>
                    <Binding Path="FirstName" FallbackValue=""/>
                </MultiBinding>
            </TextBox.Text>

If a binding is not successful, i.e. the path to the binding source is not found or the value converter , if any, fails, a DependencyProperty.UnsetValue is returned, then the target property is set to the FallbackValue, if you defined one of course.