Hello,

I use a business layer which I wan´t to bind to Windows Forms
controls. I make heavy use of interfaces, I now I have a problem:

I attached a sample Project to show the problem:

When you test this little application, you will see the the databinding
of comboBox1 will work fine (the setter of the property
"ProfessionWorking" occurs), but the databinding of comboBox2 does not
work (the setter or property "ProfessionNotWorking" does not occur).

I found a reason why problem occurs: In the private Method
System.Windows.Forms.Binding.ParseObject(), the type of the assigned
value is compared with the type of the property, and here the
Type.IsSubclassOf() Method is used. The problem is, that this Method
does only work for classes, not for interfaces.

I think this is a bug in the .NET Framework, they should use
Type.IsAssignableFrom instead, then it work.

So, what are my options?

Thanks for your answers.

Dirk

Here is the sample:

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Text;
using System.Windows.Forms;

namespace BindingProblem
{
   public partial class Form1 : Form
   {
       public Form1 ()
       {
           InitializeComponent();

           BindingList<IProfession> list = new
BindingList<IProfession>();
           list.Add(new Profession("Butcher"));
           list.Add(new Profession("Architect"));
           list.Add(new Profession("Painter"));
           list.Add(new Profession("Developer"));

           BindingList<IProfession> list2 = new
BindingList<IProfession>();
           list2.Add(new Profession("Butcher"));
           list2.Add(new Profession("Architect"));
           list2.Add(new Profession("Painter"));
           list2.Add(new Profession("Developer"));

           comboBox1.DataSource = list;
           comboBox2.DataSource = list2;

           comboBox1.DataBindings.Add("SelectedItem", m_Employee,
"ProfessionWorking");
           comboBox2.DataBindings.Add("SelectedItem", m_Employee,
"ProfessionNotWorking");
       }

       Employee m_Employee = new Employee();

       private ComboBox comboBox1;
       private ComboBox comboBox2;

               /// <summary>
       /// Erforderliche Designervariable.
       /// </summary>
       private System.ComponentModel.IContainer components = null;

       /// <summary>
       /// Verwendete Ressourcen bereinigen.
       /// </summary>
       /// <param name="disposing">True, wenn verwaltete Ressourcen
gelöscht werden sollen; andernfalls False.</param>
       protected override void Dispose (bool disposing)
       {
           if (disposing && (components != null))
           {
               components.Dispose();
           }
           base.Dispose(disposing);
       }

       #region Vom Windows Form-Designer generierter Code

       /// <summary>
       /// Erforderliche Methode für die Designerunterstützung.
       /// Der Inhalt der Methode darf nicht mit dem Code-Editor
geändert werden.
       /// </summary>
       private void InitializeComponent ()
       {
           this.comboBox1 = new System.Windows.Forms.ComboBox();
           this.comboBox2 = new System.Windows.Forms.ComboBox();
           this.SuspendLayout();
           //
           // comboBox1
           //
           this.comboBox1.DropDownStyle =
System.Windows.Forms.ComboBoxStyle.DropDownList;
           this.comboBox1.FormattingEnabled = true;
           this.comboBox1.Location = new System.Drawing.Point(12, 12);
           this.comboBox1.Name = "comboBox1";
           this.comboBox1.Size = new System.Drawing.Size(121, 21);
           this.comboBox1.TabIndex = 0;
           //
           // comboBox2
           //
           this.comboBox2.DropDownStyle =
System.Windows.Forms.ComboBoxStyle.DropDownList;
           this.comboBox2.FormattingEnabled = true;
           this.comboBox2.Location = new System.Drawing.Point(12, 40);
           this.comboBox2.Name = "comboBox2";
           this.comboBox2.Size = new System.Drawing.Size(121, 21);
           this.comboBox2.TabIndex = 1;
           //
           // Form1
           //
           this.AutoScaleDimensions = new System.Drawing.SizeF(6F,
13F);
           this.AutoScaleMode =
System.Windows.Forms.AutoScaleMode.Font;
           this.ClientSize = new System.Drawing.Size(292, 266);
           this.Controls.Add(this.comboBox2);
           this.Controls.Add(this.comboBox1);
           this.Name = "Form1";
           this.Text = "Form1";
           this.ResumeLayout(false);

       }

       #endregion

       /// </summary>
       [STAThread]
       static void Main ()
       {
           Application.EnableVisualStyles();
           Application.SetCompatibleTextRenderingDefault(false);
           Application.Run(new Form1());
       }
   }

   public class Employee
   {
       Profession m_ProfessionNotWorking;
       public IProfession ProfessionNotWorking
       {
           get
           {
               return m_ProfessionNotWorking;
           }
           set
           {
               m_ProfessionNotWorking = value as Profession;
           }
       }

       Profession m_ProfessionWorking;
       public Profession ProfessionWorking
       {
           get
           {
               return m_ProfessionWorking;
           }
           set
           {
               m_ProfessionWorking = value;
           }
       }
   }

   public class Profession : IProfession
   {
       private string profession;
       public Profession (string arg)
       {
           profession = arg;
       }

       public override string ToString ()
       {
           return profession;
       }

       public string Description
       {
           get
           {
               return profession;
           }

       }

   }

   public interface IProfession
   {
       string Description
       {
           get;
       }
   }
}