[Solved] 'Nullable' GridViewComboBoxColumn

[John]

Greetings,

I have cooked up a simple example that hopefully illustrates what I am trying to accomplish. Consider the following:

I have a Person business object that is defined as such. I've eliminated the INotifyPropertyChanged implementation to keep things clear. Note that Person.PetType is a nullable enum.

 public class Person
 {
    public Person() { }

    public string Name { get; set; }

    public int Age { get; set; }

    public PetType? PetType { get; set; }
}

public enum PetType
{
    Dog = 1,
    Cat = 2,
    Cow = 3
}

Simply put, I would like to edit a list of Person business objects in a RadGridView with a GridViewComboBoxColumn in the PetType column that will allow the user to select between Dog, Cat, Cow, and None (null).

I construct my RadGridView the following way:

this.RadGridView.Columns.Add(new GridViewDataColumn() { UniqueName = "Name", DataType = typeof(string) });
this.RadGridView.Columns.Add(new GridViewDataColumn() { UniqueName = "Age", DataType = typeof(int) });

GridViewComboBoxColumn comboBoxColumn = new GridViewComboBoxColumn();
comboBoxColumn.UniqueName = "PetType";
comboBoxColumn.DataType = typeof(PetType?);
comboBoxColumn.DataMemberBinding = new Binding()
{
  Mode = BindingMode.TwoWay,
  Path = new PropertyPath("PetType"),
  Converter = new ValueConverter()
};

comboBoxColumn.SelectedValueMemberPath = "Id";
comboBoxColumn.DisplayMemberPath = "Code";

comboBoxColumn.ItemsSource = GetPetsList();

this.RadGridView.Columns.Add(comboBoxColumn);

 this.RadGridView.ItemsSource = GetPersons();

The method for GetPetsList() is defined as follows:

private IEnumerable<ValueListItem> GetPetsList()
{
    List<ValueListItem> pets = new List<ValueListItem>();
    pets.Add(new ValueListItem() { Id = null, Code = "(None)" });
    pets.Add(new ValueListItem() { Id = 1, Code = "(Dog) Dog" });
    pets.Add(new ValueListItem() { Id = 2, Code = "(Cat) Cat" });
    pets.Add(new ValueListItem() { Id = 3, Code = "(Cow) Cow" });

    return pets.AsEnumerable();
}

ValueListItem is a simple class that i thought would help facilitate the picklist creation. It has two members Id (int?) and Code (string).

I believe I have implemented the ValueConverter correctly. I was hoping it would convert the PetType enum value (or null) from the business object to an integer (or null) for databinding. Similarly, I was hoping it would convert integers (or null) from databinding to a PetType enum value (or null) for the business object. Make sense?

    public class ValueConverter : IValueConverter
    {
        public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
        {
            if (value != null)
            {
                return (int)value;
            }

            return null;
        }

        public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
        {
            if (value != null)
            {
                int i;
                if (Int32.TryParse(value.ToString(), out i))
                {
                    return Enum.ToObject(typeof(PetType), i);
                }
            }

            return null;
        }
    }

For the sake of brevity, I'm not providing the GetPersons() method. It simply returns an IEnumerable<Person>.

Everything works great until I add in the 'null' item in the GetPetsList() method. When I add the null item, my Silverlight application crashes. I managed to get a stack trace once...

   at Telerik.Windows.Controls.LookupValueConverter.GetValueToDisplay(Object value, IEnumerable items, String pathToDisplayMember, String pathToValueMember)
   at Telerik.Windows.Controls.LookupValueConverter.Convert(Object value, Type targetType, Object parameter, CultureInfo culture)
   at Telerik.Windows.Controls.GridViewComboBoxColumn.ConvertValueToContent(Object value)
   at Telerik.Windows.Controls.GridView.GridViewCellBase.ConvertValueToContent(Object value)
   at Telerik.Windows.Controls.GridView.GridViewCell.OnValueChanged(DependencyObject dependencyObject, DependencyPropertyChangedEventArgs e)
   at Telerik.Windows.PropertyMetadata.<>c__DisplayClass1.<Create>b__0(DependencyObject d, DependencyPropertyChangedEventArgs e)
   at System.Windows.DependencyObject.SetValueInternal(DependencyProperty dp, Object value, Boolean allowReadOnlySet, Boolean isSetByStyle, Boolean isSetByBuiltInStyle)
   at System.Windows.DependencyObject.SetValueInternal(DependencyProperty dp, Object value)
   at System.Windows.DependencyObject.SetValue(DependencyProperty dp, Object value)
   at Telerik.Windows.Controls.GridView.GridViewCell.set_Value(Object value)
   at Telerik.Windows.Controls.GridView.EditContext.CommitValidContent(GridViewCell cell)
   at Telerik.Windows.Controls.GridView.EditContext.CommitCellEdit(GridViewCell cell)
   at Telerik.Windows.Controls.GridView.EditContext.TryCommitPreviouslyEditedCell(GridViewCell cell)
   at Telerik.Windows.Controls.GridView.EditContext.TryCommitPreviouslyEditedData(GridViewCell cell)
   at Telerik.Windows.Controls.GridView.EditContext.TryMakeCellCurrent(GridViewCell cell)
   at Telerik.Windows.Controls.GridView.GridViewCell.IsCurrentChanged(DependencyObject dependencyObject, DependencyPropertyChangedEventArgs e)
   at Telerik.Windows.PropertyMetadata.<>c__DisplayClass1.<Create>b__0(DependencyObject d, DependencyPropertyChangedEventArgs e)
   at System.Windows.DependencyObject.RaisePropertyChangeNotifications(DependencyProperty dp, Object newValue, Object oldValue)
   at System.Windows.DependencyObject.SetValueInternal(DependencyProperty dp, Object value, Boolean allowReadOnlySet, Boolean isSetByStyle, Boolean isSetByBuiltInStyle)
   at System.Windows.DependencyObject.SetValueInternal(DependencyProperty dp, Object value)
   at System.Windows.DependencyObject.SetValue(DependencyProperty dp, Object value)
   at Telerik.Windows.Controls.GridView.GridViewCell.set_IsCurrent(Boolean value)
   at Telerik.Windows.Controls.GridView.GridViewCell.OnGotFocus(RoutedEventArgs e)
   at System.Windows.Controls.Control.OnGotFocus(Control ctrl, EventArgs e)
   at MS.Internal.JoltHelper.FireEvent(IntPtr unmanagedObj, IntPtr unmanagedObjArgs, Int32 argsTypeIndex, String eventName)

I am using the Q2/2009 controls for Silverlight 2. Any thoughts on what I could be doing wrong? Any ideas on a work around if this is not supported behvior? We really need this type of functionality for our application.

Thanks!

[Stefan Dobrev]

Hello John,

Thanks for reporting this problem. It is a bug in our code base that we have already fix. The fix will be available in our service pack release targeted for the first half of August.

Thanks again for pointing this issue. I have updated your telerik points.

Sincerely yours,
Stefan Dobrev
the Telerik team

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[John]

Thanks for the response. We will be anxiously awaiting this SP.