How to avoid default text in textbox? - wpf

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.