How to implement WPF Binding programmatically (not XAML) with TwoWay binding mode?

Question

I have implemented some Dependency Properties in a c# class A as documented to mimic a very simple Control. In class B the Bindings and CLR Properties are implemented using the INotifyPropertyChange interface. Sending data from B to A works fine with binding mode OneWay. Sending data from B to A for updating and receiving the changed data back in B using the same DP with TwoWay mode results in the original data from B sent back from A.

Some help how to code the Receive/Update/Sentback logic in class A is highly appreciated.

Regards

Jörg

Answer 1

You could refer to the following code.

Custom Control:

public class AControl1 : Control
    {
        public static readonly DependencyProperty TestPropProperty =
        DependencyProperty.Register("TestProp", typeof(string), typeof(AControl1), new UIPropertyMetadata(null));

        public string TestProp
        {
            get { return (string)GetValue(TestPropProperty); }
            set { SetValue(TestPropProperty, value); }
        }

        static AControl1()
        {
            DefaultStyleKeyProperty.OverrideMetadata(typeof(AControl1), new FrameworkPropertyMetadata(typeof(AControl1)));
        }
    }

Generic.xaml:

<ResourceDictionary
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:local="clr-namespace:DatabindingCodebehind">


    <Style TargetType="{x:Type local:AControl1}">
        <Setter Property="Template">
            <Setter.Value>
                <ControlTemplate TargetType="{x:Type local:AControl1}">
                    <Border Background="{TemplateBinding Background}"
                            BorderBrush="{TemplateBinding BorderBrush}"
                            BorderThickness="{TemplateBinding BorderThickness}">
                        <StackPanel>
                            <TextBlock Text="Testing..."  Height="50"/>
                            <Separator />
                            <Label Height="50" Content="{Binding TestProp, RelativeSource={RelativeSource Mode=TemplatedParent}}"  />
                        </StackPanel>
                    </Border>
                </ControlTemplate>
            </Setter.Value>
        </Setter>
    </Style>
</ResourceDictionary>

MainWindow.xaml:

<Grid x:Name="grid">
</Grid>

MainWindow.xaml.cs:

using System.ComponentModel;
using System.Runtime.CompilerServices;
using System.Windows;
using System.Windows.Data;
using System.Windows.Media;

namespace DatabindingCodebehind
{
    public partial class MainWindow : Window,INotifyPropertyChanged
    {

        AControl1 a = new AControl1();
        public MainWindow()
        {
            InitializeComponent();
            grid.Children .Add (a);
            a.Height = 150;
            a.Width = 100;
            a.Background = Brushes.AliceBlue;
            TestObject myDataObject = new TestObject("name1");
            Binding myBinding = new Binding("Name");
            myBinding.Source = myDataObject;
            myBinding.Mode = BindingMode.TwoWay;
            a.SetBinding(AControl1.TestPropProperty, myBinding);
        }
        public event PropertyChangedEventHandler PropertyChanged;
        protected void OnPropertyChanged([CallerMemberName] string name = null)
        {
            PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(name));
        }
    }

    public class TestObject : INotifyPropertyChanged
    {
        public event PropertyChangedEventHandler PropertyChanged;
        protected void OnPropertyChanged(string PropertyName)
        {
            if (PropertyChanged != null)
                PropertyChanged(this, new PropertyChangedEventArgs(PropertyName));
        }
        public TestObject() { }
        public TestObject(string Name) 
        {
            _Name = Name;
        }
        private int _id;
        public int Id
        {
            get { return _id; }
            set { _id = value; OnPropertyChanged("Id"); }
        }

        private string _Name;
        public string Name
        {
            get { return _Name; }
            set { _Name = value; OnPropertyChanged("Name"); }
        }
    }
}

The result:

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