FallbackValue in WPF

One of the features of binding in WPF is the ability to support Fallback Values. Fallback Values are used when a binding comes up with an inappropriate value that in turn can't be set on the binding target. There are 2 types of Fallback Values.

TargetNullValue

As the name suggests, when a source object's property is null, the TargetNullValue is the alternate value you want to set for the target. So, whatever value is set for TargetNullValue will be set for the target. Pretty simple, isn't it ?

FallbackValue

This is used when a binding cannot determine a value at all, based on the the data source and the path. Or in other words, FallbackValue is used when the property bound to the source is not at all available. In that case, the value supplied for FallbackValue will be considered at the target end.

Getting into the code

Now, let's see the code for using both of these. Here the purpose is to bind the given text box with the EmployeeName property.

My code behind class contains just the basic code to create a property for employee name, so that we can bind it with a TextBox. Here is the code:

public partial class MainWindow : Window

{

Employee employee = new Employee();

private string _employeeName;

public string EmployeeName

{

get { return employee.Name; }

set { _employeeName = value;}

}

public MainWindow()

{

InitializeComponent();

this.DataContext = this;

employee.Name = “Mannie”;

}

}

public class Employee

{

private string _name;

public string Name

{

get { return _name; }

set { _name = value; }

}

}

And my XAML file contains the following code:

<Window x:Class="FallbackConcept.MainWindow"

xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"

xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"

xmlns:local="clr-namespace:FallbackConcept"

Title="MainWindow" Height="150" Width="325">

<Grid>

<Grid.ColumnDefinitions>

<ColumnDefinition Width="auto"/>

<ColumnDefinition Width="auto"/>

</Grid.ColumnDefinitions>

<Label Content="Name" Width="auto"/>