WPF Binding Syntax Question

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?

CodeNaked · Accepted Answer · 2011-06-13 23:43:59Z

2

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;
}

answered Jun 13, 2011 at 23:43

CodeNaked

41.6k6 gold badges128 silver badges151 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Joel B Fant · Accepted Answer · 2011-06-13 23:48:54Z

1

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();
    }

    ...
}

edited Jun 13, 2011 at 23:48

answered Jun 13, 2011 at 23:43

Joel B Fant

24.8k4 gold badges70 silver badges69 bronze badges

2 Comments

CodeNaked Over a year ago

Since the Binding doesn't use the DataContext, I don't believe it matters when he sets that. SystemFonts would need to be set before the binding is even created (i.e. InitializeComponent).

Joel B Fant Over a year ago

@CodeNaked: I write fast first, then edit a few times. :) Fixed it prior to seeing your comment.

Collectives™ on Stack Overflow

WPF Binding Syntax Question

2 Answers 2

Comments

2 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

2 Comments

Your Answer

Sign up or log in

Post as a guest

Related