C# 4 and .NET 4

Data Binding ❘ 1051
< Label >
< Label.Content >
< PriorityBinding >
< Binding Path="ProcessSomeData" Source="{StaticResource data1}"
IsAsync="True" / >
< Binding Path="Info2" Source="{StaticResource info}"
IsAsync="True" / >
< Binding Path="Info1" Source="{StaticResource info}"
IsAsync="False" / >
< /PriorityBinding >
< /Label.Content >
< /Label >
With the start of the application you can see the message please wait … in the user interface. After a few
seconds the result from the Info2 property is returned as please wait a little more . It replaces the
output from Info1 . Finally, the result from ProcessSomeData replaces the output again.
Value Conversion
Let ’ s get back to the BooksDemo application. The authors of the book are still missing in the user interface.
If you bind the Authors property to a Label element, the ToString() method of the Array class is
invoked, which returns the name of the type. One solution to this is to bind the Authors property to a
ListBox . For the ListBox , you can defi ne a template for a specifi c view. Another solution is to convert the
string array returned by the Authors property to a string and use the string for binding.
The class StringArrayConverter converts a string array to a string. WPF converter classes must
implement the interface IValueConverter from the namespace System.Windows.Data . This interface
defi nes the methods Convert() and ConvertBack() . With the StringArrayConverter , the Convert()
method converts the string array from the variable value to a string by using the String.Join() method.
The separator parameter of the Join() is taken from the variable parameter received with the
Convert() method.
You can read more about the methods of the String classes in Chapter 9, “ Strings and
Regular Expressions.”
using System;
using System.Diagnostics.Contracts;
using System.Globalization;
using System.Windows.Data;
namespace Wrox.ProCSharp.WPF.Utilities
{
[ValueConversion(typeof(string[]), typeof(string))]
class StringArrayConverter : IValueConverter
{
public object Convert(object value, Type targetType, object parameter,
CultureInfo culture)
{
Contract.Requires(value is string[]);
Contract.Requires(parameter is string);
string[] stringCollection = (string[])value;
string separator = (string)parameter;
}
return String.Join(separator, stringCollection);
public object ConvertBack(object value, Type targetType, object parameter,
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