Databind from XAML to code behind

Question

I have this Text dependency property in code behind:

public static DependencyProperty TextProperty =
        DependencyProperty.Register("Text", typeof(string), typeof(MainWindow),
        new PropertyMetadata("Hello world"));

public string Text {
    get { return (string)GetValue(TextProperty); }
    set { SetValue(TextProperty, value); }
}

I want to bind content of label to that Text property so that the label displays actual value of Text property and vice-versa.

<Label Content="{Binding ???}" />

How can I do it ?

I have done that some time before but now I cannot remember how - and it is very simple. The simplest code will be accepted.

Answer 1

Set DataContext of your Window/Control to the same class and then specify the path on the binding, something like this:

public class MyWindow : Window {

    public MyWindow() {
        InitializeComponents();
        DataContext = this;
    }

    public string Text { ... }    
}

Then in your xaml:

<Label Content="{Binding Path=Text}">

Answer 2

You have to set the DataContext of the window for it to work. XAML:

<Window x:Class="WpfApplication2.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="MainWindow" Height="350" Width="525" 
        DataContext="{Binding RelativeSource={RelativeSource Self}}">
    <Grid>
      <StackPanel>
        <Label Content="{Binding Text}" />
        <Button Content="Click me" Click="HandleClick" />
      </StackPanel>

    </Grid>
</Window>

Code-behind:

/// <summary>
/// Interaction logic for MainWindow.xaml
/// </summary>
public partial class MainWindow : Window
{
    public static DependencyProperty TextProperty = DependencyProperty.Register("Text", typeof(string), typeof(MainWindow), new PropertyMetadata("Hello world"));
    public string Text 
    { 
        get { return (string)GetValue(TextProperty); } 
        set { this.SetValue(TextProperty, value); } 
    }

    public MainWindow()
    {
        InitializeComponent();
    }

    protected void HandleClick(object sender, RoutedEventArgs e)
    {
        this.Text = "Hello, World";
    }
}

Answer 3

Setting DataContext in XAML to Code-Behind can be a little bit tricky but in general these situation are the most common:

1. You want to make the DataContext the the whole Window or Custom UserControl

.

<Window
blahhhh..
DataContext={Binding RelativeSource={RelativeSource Mode=Self}}>

or

<UserControl
Blahhhh....
DataContext={Binding RelativeSource={RelativeSource Mode=Self}}>

2. if you set the DataContext of the Window or user control to something else than the code behind and have a child control you would need to set it's DataContext to the Code-Behind you can use the following:

<Label DataContext={Binding RelativeSource={RelativeSource Mode=FindAncestor,AncestorType=Window}}/>

for custom UserControl :

<Label DataContext={Binding RelativeSource={RelativeSource Mode=FindAncestor,AncestorType=UserControl}}/>

in this Case setting the DataContext to self, will make Binding refer to the Label Object itself not the Control's Code-Behind. I hope that will help.