How do I create a XAML binding to a member variable?

Question

I'm new to XAML and data binding. I want to define a GUI control in MainWindow.xaml that gets its data from a member variable in MainWindow.xaml.cs. For simplicity's sake I just made a program that displays a counter as well as a button to increment the counter.

Based on earlier threads I've looked up, I came up with the following code:

MainWindow.xaml.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Navigation;
using System.Windows.Shapes;

namespace XAMLBindingTest
{
    /// <summary>
    /// Interaction logic for MainWindow.xaml
    /// </summary>
    public partial class MainWindow : Window
    {
        private int Counter
        {
            get { return (int)GetValue(CounterProperty); }
            set { SetValue(CounterProperty, value); }
        }
        public static readonly DependencyProperty CounterProperty = 
            DependencyProperty.Register("Counter", typeof(int), typeof(MainWindow), new PropertyMetadata(null));

        public MainWindow()
        {
            Counter = 0;
            InitializeComponent();
        }

        private void incrementCounter(object sender, RoutedEventArgs e)
        {
            ++Counter;
        }
    }
}

MainWindow.xaml

<Window x:Class="XAMLBindingTest.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="MainWindow" Height="140" Width="180">
    <Grid>
        <StackPanel HorizontalAlignment="Left" VerticalAlignment="Top">
            <TextBlock x:Name="txbCounter" HorizontalAlignment="Left" TextWrapping="Wrap" Text="{Binding Counter}" VerticalAlignment="Top"/>
            <Button x:Name="btnIncrement" Content="Increment" Width="75" Click="incrementCounter"/>
        </StackPanel>
    </Grid>
</Window>

This example compiles, but the TextBlock isn't showing a counter value. How do I wire the TextBlock to the Counter member in a correct way?

Answer 1

Try adding a "Name" to your window and binding using "ElementName"

<Window x:Class="XAMLBindingTest.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" Name="UI">
    <Grid>
        <StackPanel HorizontalAlignment="Left" VerticalAlignment="Top">
            <TextBlock x:Name="txbCounter" HorizontalAlignment="Left" TextWrapping="Wrap" Text="{Binding ElementName=UI, Path=Counter}" VerticalAlignment="Top"/>
            <Button x:Name="btnIncrement" Content="Increment" Width="75" Click="incrementCounter"/>
        </StackPanel>
    </Grid>

</Window>