Nullable ComboBox.SelectedValue

Here's what I hacked out of the nullable DateTimePicker to work for the SelectedValue property of a ComboBox

        /// <summary>
        /// From BReusable
        /// </summary>
        /// <param name="comboBox"></param>
        /// <param name="dataSource"></param>
        /// <param name="valueMember"></param>

        /// <remarks>With help from Dan Hanan at http://blogs.interknowlogy.com/danhanan/archive/2007/01/21/10847.aspx</remarks>

        public static void BindNullableSelectedValue(this ComboBox comboBox, BindingSource dataSource, String valueMember)

        {

            var binding = new Binding(Member.Name<ComboBox>(item=>item.SelectedValue), dataSource, valueMember, true);



            //OBJECT PROPERTY --> CONTROL VALUE

            binding.Format += ((sender, e) =>

            {

                Binding b = sender as Binding;



                if (b != null)

                {

                    var  cBox = (binding.Control as ComboBox);

                    if (cBox != null)

                    {

                        if (e.Value == null)

                        {



                            cBox.SelectedItem=null;



                        }

                    }



                }

            });

            // CONTROL VALUE --> OBJECT PROPERTY

            binding.Parse += ((sender, e) =>

            {

                // e.value is the formatted value coming from the control.
                // we change it to be the value we want to stuff in the object.

                var b = sender as Binding;



                if (b != null)

                {

                    var cBox = (b.Control as ComboBox);

                    if (cBox != null)

                    {

                        e.Value = cBox.SelectedItem != null ? cBox.SelectedValue : null;

                    }

                }

            });

            comboBox.DataBindings.Add(binding);



        }

- Formatted via Jeff Atwood's - ModernText Visual Studio Macro

nullable DateTimePicker databinding

Code or special controls to allow a DateTimePicker to accept a nullable value are all over the place. Here's the one I'm using that is working well so far.

/// <summary>

        /// From BReusable

        /// </summary>

        /// <param name="dateTimePicker"></param>

        /// <param name="dataSource"></param>

        /// <param name="valueMember"></param>

        /// <param name="showCheckBox"></param>

        /// <remarks>With help from Dan Hanan </remarks>

        public static void BindNullableValue(this DateTimePicker dateTimePicker, BindingSource dataSource, String valueMember,bool showCheckBox)

        {

            var binding = new Binding("Value", dataSource, valueMember, true);



            //OBJECT PROPERTY --> CONTROL VALUE

            binding.Format += ((sender, e) =>

                                   {

                                       Binding b = sender as Binding;

                

                                       if (b != null)

                                       {

                                           DateTimePicker dtp = (binding.Control as DateTimePicker);

                                           if (dtp != null)

                                           {

                                               if (e.Value == null)

                                               {



                                                   dtp.ShowCheckBox = showCheckBox;

                                                   dtp.Checked = false;



                                           // have to set e.Value to SOMETHING, since it's coming in as NULL
                                           // if i set to DateTime.Today, and that's DIFFERENT than the control's current
                                           // value, then it triggers a CHANGE to the value, which CHECKS the box (not ok)
                                           // the trick - set e.Value to whatever value the control currently has. 
                                           // This does NOT cause a CHANGE, and the checkbox stays OFF.



                                                   e.Value = dtp.Value;



                                               }

                                               else

                                               {

                                                   dtp.ShowCheckBox = showCheckBox;

                                                   dtp.Checked = true;

                                           // leave e.Value unchanged - it's not null, so the DTP is fine with it.

                                               }



                                           }



                                       }

                                   });

            // CONTROL VALUE --> OBJECT PROPERTY

            binding.Parse += ((sender, e) =>

                                  {

                                      // e.value is the formatted value coming from the control. 

                                      // we change it to be the value we want to stuff in the object.

                                      var b = sender as Binding;



                                      if (b != null)

                                      {

                                          var dtp = (b.Control as DateTimePicker);

                                          if (dtp != null)

                                          {

                                              if (dtp.Checked == false)

                                              {

                                                  dtp.ShowCheckBox = showCheckBox;

                                                  dtp.Checked = false;

                                                //used to cast null to dateTime?

                                                  e.Value = null;

                                              }

                                              else

                                              {

                                                  DateTime val = Convert.ToDateTime(e.Value);

                                                  e.Value = val;

                                              }

                                          }

                                      }

                                  });

            dateTimePicker.DataBindings.Add(binding);



        }

DataTimePicker databinding vs nullable DateTime

I just came across an interesting problem. You can't bind a nullable dateTime directly to a dateTimePicker. At least not easily. Here's an extension method that handles the heavy lifting.

/// <summary>

/// 

/// </summary>

/// <param name="dtp"></param>

/// <param name="dataSource"></param>

/// <param name="valueMember"></param>

/// <remarks>With help from Dan Hanan at http://blogs.interknowlogy.com/danhanan/archive/2007/01/21/10847.aspx</remarks>

public static void BindNullableValue(this DateTimePicker dateTimePicker, BindingSource dataSource, String valueMember)

{

var binding = new Binding("Value", dataSource, valueMember, true);

//OBJECT PROPERTY --> CONTROL VALUE

binding.Format += new ConvertEventHandler((sender, e) =>

{

Binding b = sender as Binding;

if (b != null)

{

DateTimePicker dtp = (binding.Control as DateTimePicker);

if (dtp != null)

{

if (e.Value == null)

{

dtp.ShowCheckBox = true;

dtp.Checked = false;

// have to set e.Value to SOMETHING, since it's coming in as NULL

// if i set to DateTime.Today, and that's DIFFERENT than the control's current

// value, then it triggers a CHANGE to the value, which CHECKS the box (not ok)

// the trick - set e.Value to whatever value the control currently has. 

// This does NOT cause a CHANGE, and the checkbox stays OFF.

e.Value = dtp.Value;

}

else

{

dtp.ShowCheckBox = true;

dtp.Checked = true;

// leave e.Value unchanged - it's not null, so the DTP is fine with it.

}

}

}

});

// CONTROL VALUE --> OBJECT PROPERTY

binding.Parse += new ConvertEventHandler((sender, e) => {

// e.value is the formatted value coming from the control. 

// we change it to be the value we want to stuff in the object.

Binding b = sender as Binding;

if (b != null)

{

DateTimePicker dtp = (b.Control as DateTimePicker);

if (dtp != null)

{

if (dtp.Checked == false)

{

dtp.ShowCheckBox = true;

dtp.Checked = false;

e.Value = (Nullable<DateTime>) null;

}

else

{

DateTime val = Convert.ToDateTime(e.Value);

e.Value =val;

}

}

}

});

dateTimePicker.DataBindings.Add(binding);

}