Binding does not update as expected

Question

I create a simple UserControl , DoubleDatePicker , which defines DependencyProperty , SelectedDate :

DoubleDatePicker.xaml :

<UserControl x:Class="TestWpfDoubleDatePicker.DoubleDatePicker"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:toolkit="http://schemas.microsoft.com/wpf/2008/toolkit">    
<StackPanel x:Name="LayoutRoot" Background="White">
    <toolkit:DatePicker x:Name="DateInput" SelectedDate="{Binding SelectedDate,Mode=TwoWay}" Margin="5,0,5,0" />
    <TextBlock Text="{Binding SelectedDate}" />
    <toolkit:DatePicker SelectedDate="{Binding SelectedDate,Mode=TwoWay}" Margin="5,0,5,0" />
</StackPanel>

DoubleDatePicker.xaml.cs :

using System;
using System.Windows;
using System.Windows.Controls;


namespace TestWpfDoubleDatePicker
{
    public partial class DoubleDatePicker : UserControl
    {
        public static readonly DependencyProperty SelectedDateProperty =
        DependencyProperty.Register("SelectedDate", typeof(DateTime), typeof(DoubleDatePicker), null);

        public DateTime SelectedDate
        {
            get { return (DateTime)this.GetValue(SelectedDateProperty); }
            set { this.SetValue(SelectedDateProperty, value); }
        }

        public DoubleDatePicker()
        {
            this.InitializeComponent();

            this.DataContext = this;
        }
    }
}

I would like to bind the SelectedDate property from the outside, but it's not so simple. Here is an example of code that tries to get the value of a property in a TextBlock :

MainWindow.xaml :

<Window x:Class="TestWpfDoubleDatePicker.MainWindow"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:local="clr-namespace:TestWpfDoubleDatePicker"
    Title="MainWindow" Height="350" Width="525">
<StackPanel x:Name="LayoutRoot" Background="White">
    <local:DoubleDatePicker x:Name="ddp" SelectedDate="{Binding SelectedDate}" />
    <Button Content="Update" Click="Button_Click" />
    <TextBlock Text="{Binding SelectedDate}" />
</StackPanel>

and MainWindow.xaml.cs :

using System;
using System.Windows;

namespace TestWpfDoubleDatePicker
{
    /// <summary>
    /// Interaction logic for MainWindow.xaml
    /// </summary>
    public partial class MainWindow : Window
    {
        public static readonly DependencyProperty SelectedDateProperty =
            DependencyProperty.Register("SelectedDate", typeof(DateTime), typeof(MainWindow), null);

        public DateTime SelectedDate
        {
            get { return (DateTime)this.GetValue(SelectedDateProperty); }
            set { this.SetValue(SelectedDateProperty, value); }
        }

        public MainWindow()
        {
            InitializeComponent();

            this.DataContext = this;
        }

        private void Button_Click(object sender, RoutedEventArgs e)
        {
            this.SelectedDate = this.ddp.SelectedDate;
        }
    }
}

DoubleDatePicker : SelectedDate DatePicker, TextBlock DoubleDatePicker , .

, TextBlock MainWindow SelectedDate > DoubleDatePicker - , .

?

Visual Studio Professional 2010 WPF 4.

.

Answer 1

, , DataContext :

this.DataContext = this;

DatePicker , DatePicker. , , DatePicker;).

, DatePicker, XAML DatePicker, ElementName RelativeSource .

, ;)

XAML DatePicker ElementName:

<UserControl x:Class="TestWpfDoubleDatePicker.DoubleDatePicker"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:toolkit="http://schemas.microsoft.com/wpf/2008/toolkit" 
x:Name="Root">    
<StackPanel x:Name="LayoutRoot" Background="White">
    <toolkit:DatePicker x:Name="DateInput" SelectedDate="{Binding ElementName=Root, Path=SelectedDate,Mode=TwoWay}" Margin="5,0,5,0" />
    <TextBlock Text="{Binding ElementName=Root, Path=SelectedDate}" />
    <toolkit:DatePicker SelectedDate="{Binding ElementName=Root, Path=SelectedDate,Mode=TwoWay}" Margin="5,0,5,0" />
</StackPanel>