How to debug databinding

Question

I'm new to data-binding and I am having a hard-time setting it up for my WPF application:

I have a class Test which implements INotifyPropertyChanged and a property Text.

When I do this in the code-behind:

Binding b = new Binding("Text");
b.Source = Test;
label1.SetBinding(ContentProperty, b);

everything works great.

When I do the same thing in XAML:

Content="{Binding Source=Window.Test, Path=Text}"

The label content does not update.

I would like to avoid having to do this in the code-behind, what am I doing wrong?

Look in your Output Window, there will be an exception that tells you what went wrong. — Henk Holterman
– Henk Holterman, Commented Feb 20, 2012 at 19:24

Thomas Levesque · Accepted Answer · 2012-02-20 19:22:46Z

1

The easiest solution is to give a name to the Window in XAML (e.g. root) and use ElementName to define the binding source:

Content="{Binding ElementName=root, Path=Test.Text}"

answered Feb 20, 2012 at 19:22

Thomas Levesque

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2 Comments

user472875 Over a year ago

Solved my problem. One thing, when I try to use the Properties Window to set the Content, I select ElementName to root but Test does not appear in the choice list, so I have to enter the code manually. Is there any way to make it appear, or is this impossible for this situation?

Thomas Levesque Over a year ago

@user472875, the designer sees that root is of type Window, so it looks for properties declared in the Window class, not properties declared in your specific window...

Sergey Vyacheslavovich Brunov · Accepted Answer · 2012-02-20 19:28:54Z

0

For simplicity, set the window DataContext to your Test instance:

public partial class MainWindow : Window
{   
    public MainWindow()
    {
        InitializeComponent();
        DataContext = new Test
            {
                Text = "Hello, World!"
            };
    }
}

Then declare databinding in XAML:

Content="{Binding Path=Text}"

answered Feb 20, 2012 at 19:28

Sergey Vyacheslavovich Brunov

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Comments

brunnerh · Accepted Answer · 2012-02-21 03:58:55Z

what am I doing wrong?

You are making unfounded assumptions about how something ought to work about which you do not have much of a clue. You are dealing with two fundamentally different languages here and just because you want WPF to interpret Window.Test as a reference to some specific window you had in mind does not make it so.

XAML is fundamentally string-based, for the most part strings are converted to primitive types like ints and doubles, e.g. when you set the height of a control you pass a string to a property of type double. The XAML parser knows via reflection that the property is of type double and tries to convert the string (using a default value converter if no other has been specified). Now what do you think happens if a property is of type object? What is the parser to do? Well, it is not going to do anything as a string is already an object.

Guess what type Binding.Source has and what the source object of your binding will be when you write Window.Test...

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