New to Telerik UI for ASP.NET AJAX? Download free 30-day trial

Implement Custom Sorting

Sorting items by Value

By default, RadComboBox sorts items by their Text property. This article will show you how to implement custom sorting - the items will be sorted by their Value property.

For this purpose, we will use the IComparer interface which exposes a method that compares two objects.

Here are the two steps that you need to perform:

  1. Create a class that implements IComparer for your custom sorting:

public class SortComboItemsByValue : IComparer
{
   public int Compare(object x, object y)
   {
       RadComboBoxItem p1 = new RadComboBoxItem();
       RadComboBoxItem p2 = new RadComboBoxItem();
       if (x is RadComboBoxItem)
           p1 = x as RadComboBoxItem;
       else
           throw new ArgumentException("Object is not of type RadComboBoxItem.");
       if (y is RadComboBoxItem)
           p2 = y as RadComboBoxItem;
       else
           throw new ArgumentException("Object is not of type RadComboBoxItem.");
       int cmp = 0;
       if (p1.ComboBoxParent.Sort == RadComboBoxSort.Ascending)
       {
           //here we compare the Values of the items
           cmp = String.Compare(p1.Value, p2.Value, !p1.ComboBoxParent.SortCaseSensitive);
       }
       if (p1.ComboBoxParent.Sort == RadComboBoxSort.Descending)
       {
           //here we compare the Values of the items
           cmp = String.Compare(p1.Value, p2.Value, !p1.ComboBoxParent.SortCaseSensitive) * -1;
       }
       return cmp;
   }
}           

Public Class SortComboItemsByValue
    Implements IComparer
    Public Function Compare(ByVal x As Object, ByVal y As Object) As Integer Implements IComparer.Compare
        Dim p1 As New RadComboBoxItem()
        Dim p2 As New RadComboBoxItem()
        If TypeOf x Is RadComboBoxItem Then
            p1 = TryCast(x, RadComboBoxItem)
        Else
            Throw New ArgumentException("Object is not of type RadComboBoxItem.")
        End If
        If TypeOf y Is RadComboBoxItem Then
            p2 = TryCast(y, RadComboBoxItem)
        Else
            Throw New ArgumentException("Object is not of type RadComboBoxItem.")
        End If
        Dim cmp As Integer = 0
        If p1.ComboBoxParent.Sort = RadComboBoxSort.Ascending Then
            'here we compare the Values of the items
            cmp = [String].Compare(p1.Value, p2.Value, Not p1.ComboBoxParent.SortCaseSensitive)
        End If
        If p1.ComboBoxParent.Sort = RadComboBoxSort.Descending Then
            'here we compare the Values of the items
            cmp = [String].Compare(p1.Value, p2.Value, Not p1.ComboBoxParent.SortCaseSensitive) * -1
        End If
        Return cmp
    End Function
End Class

  1. Call the overloaded SortItems or Items.Sort methods passing your IComparer as a parameter:

RadComboBox2.Sort = RadComboBoxSort.Ascending;
RadComboBox2.SortItems(new SortComboItemsByValue());


RadComboBox2.Sort = RadComboBoxSort.Ascending
RadComboBox2.SortItems(New SortComboItemsByValue())

That's it. Now the combobox items will be sorted by their Values instead of Text.

Custom sorting with checked items on top

When using RadComboBox with enabled checkbox, common issue is how to bring the checked items on top of the sorted dropdown. This can be achieved by adding additional check in the custom comparer class from the sample above

Sample declaration:

<telerik:RadComboBox runat="server" AutoPostBack="true" OnItemChecked="RadComboBox1_ItemChecked" ID="RadComboBox1" CheckBoxes="true">
    <Items>
        <telerik:RadComboBoxItem Text="Item 1" Value="1" />
        <telerik:RadComboBoxItem Text="Item 2" Value="2" />
        <telerik:RadComboBoxItem Text="Item 3" Value="3" />
        <telerik:RadComboBoxItem Text="Item 4" Value="4" />
        <telerik:RadComboBoxItem Text="Item 5" Value="5" />
        <telerik:RadComboBoxItem Text="Item 6" Value="6" />
    </Items>
</telerik:RadComboBox>

Code-behind:

protected void Page_Load(object sender, EventArgs e)
{
    RadComboBox1.Sort = RadComboBoxSort.Ascending;
    RadComboBox1.SortItems(new SortCheckedComboItemsFirst());
}
public class SortCheckedComboItemsFirst : IComparer
{
    public int Compare(object x, object y)
    {
        RadComboBoxItem p1 = new RadComboBoxItem();
        RadComboBoxItem p2 = new RadComboBoxItem();
        if (x is RadComboBoxItem)
            p1 = x as RadComboBoxItem;
        else
            throw new ArgumentException("Object is not of type RadComboBoxItem.");
        if (y is RadComboBoxItem)
            p2 = y as RadComboBoxItem;
        else
            throw new ArgumentException("Object is not of type RadComboBoxItem.");
        int cmp = 0;

        if (p1.Checked)
        {
            if (p2.Checked == false)
            {
                return -1;
            }
            // uncomment for skipping the sorting of the checked items
            //else
            //{                   
            //    return 1;
            //}
        }
        else if (p2.Checked)
        {
            return 1;
        }

        if (p1.ComboBoxParent.Sort == RadComboBoxSort.Ascending)
        {
            //here we compare the Values of the items
            cmp = String.Compare(p1.Value, p2.Value, !p1.ComboBoxParent.SortCaseSensitive);
        }
        if (p1.ComboBoxParent.Sort == RadComboBoxSort.Descending)
        {
            //here we compare the Values of the items
            cmp = String.Compare(p1.Value, p2.Value, !p1.ComboBoxParent.SortCaseSensitive) * -1;
        }
        return cmp;
    }
}

protected void RadComboBox1_ItemChecked(object sender, RadComboBoxItemEventArgs e)
{

}
Protected Sub Page_Load(ByVal sender As Object, ByVal e As EventArgs) Handles Me.Load
    RadComboBox1.Sort = RadComboBoxSort.Ascending
    RadComboBox1.SortItems(New SortCheckedComboItemsFirst())
End Sub

Public Class SortCheckedComboItemsFirst
    Implements IComparer
    Public Function Compare(ByVal x As Object, ByVal y As Object) As Integer Implements IComparer.Compare
        Dim p1 As New RadComboBoxItem()
        Dim p2 As New RadComboBoxItem()

        If TypeOf x Is RadComboBoxItem Then
            p1 = TryCast(x, RadComboBoxItem)
        Else
            Throw New ArgumentException("Object is not of type RadComboBoxItem.")
        End If

        If TypeOf y Is RadComboBoxItem Then
            p2 = TryCast(y, RadComboBoxItem)
        Else
            Throw New ArgumentException("Object is not of type RadComboBoxItem.")
        End If

        Dim cmp As Integer = 0

        If p1.Checked Then

            If p2.Checked = False Then
                Return -1
            'uncomment for skipping the sorting of the checked items
            'Else
            '   Return 1
            End If
        ElseIf p2.Checked Then
            Return 1
        End If

        If p1.ComboBoxParent.Sort = RadComboBoxSort.Ascending Then
            'here we compare the Values of the items
            cmp = [String].Compare(p1.Value, p2.Value, Not p1.ComboBoxParent.SortCaseSensitive)
        End If
        If p1.ComboBoxParent.Sort = RadComboBoxSort.Descending Then
            'here we compare the Values of the items
            cmp = [String].Compare(p1.Value, p2.Value, Not p1.ComboBoxParent.SortCaseSensitive) * -1
        End If
        Return cmp
    End Function
End Class

Protected Sub RadComboBox1_ItemChecked(sender As Object, e As RadComboBoxItemEventArgs)

End Sub

See Also

In this article
Not finding the help you need? Improve this article