WPF Binding Syntax Question - wpf

Question

The code below is supposed to show a stack of three list boxes, each containing a list of all the system fonts. The first is unsorted, and the second and third are alphabetized. But the third one is empty. I don't see any binding error messages in the VS Output window when debugging.
The markup is:
<Window x:Class="FontList.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:local="clr-namespace:FontList"
Title="MainWindow" Height="600" Width="400">
<Grid>
<Grid.RowDefinitions>
<RowDefinition Height="*"></RowDefinition>
<RowDefinition Height="*"></RowDefinition>
<RowDefinition Height="*"></RowDefinition>
</Grid.RowDefinitions>
<ListBox Grid.Row="0" ItemsSource="{Binding Source={x:Static Fonts.SystemFontFamilies}}" />
<ListBox Grid.Row="1" ItemsSource="{Binding Path=SystemFonts}" />
<ListBox Grid.Row="2" ItemsSource="{Binding Source={x:Static local:MainWindow.SystemFonts}}" />
</Grid>
The code behind is:
using System.Collections.Generic;
using System.Linq;
using System.Windows;
using System.Windows.Media;
namespace FontList
{
public partial class MainWindow : Window
{
public static List<FontFamily> SystemFonts { get; set; }
public MainWindow() {
InitializeComponent();
DataContext = this;
SystemFonts = Fonts.SystemFontFamilies.OrderBy(f => f.ToString()).ToList();
}
}
}
What's wrong with the third binding?

Answer 1

You need to initialize SystemFonts before you call InitalizeComponent. The WPF binding has no way of knowing the property's value changed.
public MainWindow() {
SystemFonts = Fonts.SystemFontFamilies.OrderBy(f => f.ToString()).ToList();
InitializeComponent();
DataContext = this;
}
or better yet, use:
static MainWindow() {
SystemFonts = Fonts.SystemFontFamilies.OrderBy(f => f.ToString()).ToList();
}
public MainWindow() {
InitializeComponent();
DataContext = this;
}

Answer 2

The Bindings are created during InitializeComponent, while SystemFonts is null. After you set it, the binding has no way of knowing that the property's value has changed.
You can also set SystemFonts in a static constructor, which is probably preferable since it's a static property. Otherwise every instantiation of MainWindow will change the static property.
public partial class MainWindow : Window {
public static List<FontFamily> SystemFonts{get; set;}
static MainWindow {
SystemFonts = Fonts.SystemFontFamilies.OrderBy(f => f.ToString()).ToList();
}
...
}