Loading items from WebService

Fetching server data using ASP.NET Web Services to ensure responsive, dynamic applications with minimal overhead, enhancing both performance and user experience.

Web services are components on a Web server that a client application can call by making HTTP requests across the Web.

If you need help setting up the WebService, you can check out the Quick Walkthrough ASP.NET WebService article.

ComboBox settings for loading the items from Web Service:

• Set the EnableLoadOnDemand property to true.
• Provide the path to the Web Service and the name of the method for the Path and Method properties of the WebServiceSettings element.

Web Service specifics:

• Method return Type should be a collection of RadComboBoxItemData objects. To use custom objects, check out the Custom ComboBox Item Data section.

XML Web Service (ASMX)

ComboBox Markup

ASP.NET

<telerik:RadComboBox ID="RadComboBox1" runat="server" RenderMode="Lightweight" EnableLoadOnDemand="true">
    <WebServiceSettings Path="WebService.asmx" Method="GetProducts"></WebServiceSettings>
</telerik:RadComboBox>

Web Service method

C#

[WebMethod]
public List<RadComboBoxItemData> GetProducts(RadComboBoxContext context)
{
    string userText = context.Text;

    List<RadComboBoxItemData> allItems = Enumerable.Range(0, 100).Select(x => new RadComboBoxItemData()
    {
        Text = "Product " + x,
        Value = x.ToString()
    }).ToList();

    List<RadComboBoxItemData> filteredItems = allItems.Where(item => item.Text.Contains(userText)).ToList();

    return filteredItems;
}

VB

<WebMethod>
Public Function GetProducts(ByVal context As RadComboBoxContext) As List(Of RadComboBoxItemData)
    Dim userText As String = context.Text
    Dim allItems As List(Of RadComboBoxItemData) = Enumerable.Range(0, 100).Select(Function(x) New RadComboBoxItemData() With {
        .Text = "Product " & x,
        .Value = x.ToString()
    }).ToList()

    Dim filteredItems As List(Of RadComboBoxItemData) = allItems.Where(Function(item) item.Text.Contains(userText)).ToList()

    Return filteredItems
End Function

WCF Service (SVC)

ComboBox Markup

ASP.NET

<telerik:RadComboBox ID="RadComboBox1" runat="server" RenderMode="Lightweight" EnableLoadOnDemand="true">
    <WebServiceSettings Path="Service.svc" Method="GetProducts"></WebServiceSettings>
</telerik:RadComboBox>

Web Service method

C#

[OperationContract]
public List<RadComboBoxItemData> GetProducts(RadComboBoxContext context)
{
    string userText = context.Text;

    List<RadComboBoxItemData> allItems = Enumerable.Range(0, 100).Select(x => new RadComboBoxItemData()
    {
        Text = "Product " + x,
        Value = x.ToString()
    }).ToList();

    List<RadComboBoxItemData> filteredItems = allItems.Where(item => item.Text.Contains(userText)).ToList();

    return filteredItems;
}

VB

<OperationContract>
Public Function GetProducts(ByVal context As RadComboBoxContext) As List(Of RadComboBoxItemData)
    Dim userText As String = context.Text
    Dim allItems As List(Of RadComboBoxItemData) = Enumerable.Range(0, 100).Select(Function(x) New RadComboBoxItemData() With {
        .Text = "Product " & x,
        .Value = x.ToString()
    }).ToList()

    Dim filteredItems As List(Of RadComboBoxItemData) = allItems.Where(Function(item) item.Text.Contains(userText)).ToList()

    Return filteredItems
End Function

PageMethod

ComboBox Markup

ASP.NET

<telerik:RadComboBox ID="RadComboBox1" runat="server" RenderMode="Lightweight" EnableLoadOnDemand="true">
    <WebServiceSettings Path="Default.aspx" Method="GetProducts"></WebServiceSettings>
</telerik:RadComboBox>

CodeBehind method

C#

[WebMethod]
public static List<RadComboBoxItemData> GetProducts(RadComboBoxContext context)
{
    string userText = context.Text;

    List<RadComboBoxItemData> allItems = Enumerable.Range(0, 100).Select(x => new RadComboBoxItemData()
    {
        Text = "Product " + x,
        Value = x.ToString()
    }).ToList();

    List<RadComboBoxItemData> filteredItems = allItems.Where(item => item.Text.Contains(userText)).ToList();

    return filteredItems;
}

VB

<WebMethod>
Public Shared Function GetProducts(ByVal context As RadComboBoxContext) As List(Of RadComboBoxItemData)
    Dim userText As String = context.Text
    
    Dim allItems As List(Of RadComboBoxItemData) = Enumerable.Range(0, 100).Select(Function(x) New RadComboBoxItemData() With {
        .Text = "Product " & x,
        .Value = x.ToString()
    }).ToList()

    Dim filteredItems As List(Of RadComboBoxItemData) = allItems.Where(Function(item) item.Text.Contains(userText)).ToList()
    
    Return filteredItems
End Function

Check out the Online Examples at Load on Demand Modes.

Custom ComboBox Item Data

In case of custom models inherit the Telerik.Web.UI.ControlItemData Class.

C#

public class CustomComboItemData : ControlItemData
{
    // Inherited Members

    // Custom Members
    public string CustomField1 { get; set; }
    public string CustomField2 { get; set; }
}

VB

Public Class CustomComboItemData
    Inherits ControlItemData

    Public Property CustomField1 As String
    Public Property CustomField2 As String
End Class

Example Usage

C#

public List<CustomComboItemData> GetProducts(RadComboBoxContext context)
{
    string userText = context.Text;

    List<CustomComboItemData> allItems = Enumerable.Range(0, 100).Select(x => new CustomComboItemData()
    {
        Text = "Product " + x,
        Value = x.ToString()
    }).ToList();

    List<CustomComboItemData> filteredItems = allItems.Where(item => item.Text.Contains(userText)).ToList();

    return filteredItems;
}

VB

Public Function GetProducts(ByVal context As RadComboBoxContext) As List(Of CustomComboItemData)
    Dim userText As String = context.Text
    Dim allItems As List(Of CustomComboItemData) = Enumerable.Range(0, 100).Select(Function(x) New CustomComboItemData() With {
        .Text = "Product " & x,
        .Value = x.ToString()
    }).ToList()

    Dim filteredItems As List(Of CustomComboItemData) = allItems.Where(Function(item) item.Text.Contains(userText)).ToList()

    Return filteredItems
End Function