Question

I have written a control in C# that derives from System.Windows.Forms.Control. I have added a property Selected to which I want to databind to a business entity using a BindingSource.

I’ve implemented the PropertyNameChanged pattern by adding a SelectedChanged event that I fire when the Selected property is changed.

This is my code:

public partial class RateControl : Control {     [Category('Property Changed')]     public event EventHandler SelectedChanged;      public int Selected     {       get       { return m_selected; }       set       {         if (m_selected != value)         {           m_selected = value;           OnSelectedChanged();           Invalidate();         }       }     }      protected virtual void OnSelectedChanged()     {       if (this.SelectedChanged != null)         this.SelectedChanged(this, new EventArgs());     } } 

When I bind to the Selected property, I see the event being subscibed to. The event is also fired when the property changes.

However the business entity is not updated. I don’t even see the getter of the Selected property being accessed.

What am I missing?

Answer 1

Have you got the binding’s update mode set to DataSourceUpdateMode.OnPropertyChanged? Either via binding.DataSourceUpdateMode = DataSourceUpdateMode.OnPropertyChanged;, or using one of the DataBindings.Add(...) overloads.

The following works for me to push values to the business object…

using System; using System.Diagnostics; using System.Windows.Forms;  class MyForm : Form {     public MyForm()     {         MyBusinessObject obj = new MyBusinessObject();         Button btn = new Button();         btn.Click += delegate { Foo++; };         DataBindings.Add('Foo', obj, 'Bar', false, DataSourceUpdateMode.OnPropertyChanged);         DataBindings.Add('Text', obj, 'Bar');         Controls.Add(btn);     }      private int foo;     public event EventHandler FooChanged;     public int Foo     {         get { return foo; }         set         {             if (foo != value)             {                 foo = value;                 Debug.WriteLine('Foo changed to ' + foo);                 if (FooChanged != null) FooChanged(this, EventArgs.Empty);             }         }     } }  class MyBusinessObject {     private int bar;     public event EventHandler BarChanged;     public int Bar     {         get { return bar; }         set         {             if (bar != value)             {                 bar = value;                 Debug.WriteLine('Bar changed to ' + bar);                 if (BarChanged != null) BarChanged(this, EventArgs.Empty);             }         }     } }  static class Program {     [STAThread]     static void Main()     {         Application.Run(new MyForm());     } }