Call (Consume) Web API in ASPX Page in ASP.Net Web Forms using C#

The Web API 2 Controller method will fetch records from database using Entity Framework in ASP.Net MVC and later it will be called (consumed) in ASP.Net Web Forms (ASPX) page using WebClient class in ASP.Net.


Model
The CustomerModel class consists of the following property.
public class CustomerModel
{
    ///<summary>
    /// Gets or sets Name.
    ///</summary>
    public string Name { get; set; }
}
 
Web API Controller

In order to add a Web API Controller you will need to Right Click the Controllers folder in the Solution Explorer and click on Add and then Controller.


The next task is to register the Configuration for Web API in the Global.asax file so that the Web API is available for accessing on Web.
In order to do so open Global.asax file and add the following line.
System.Web.Http.GlobalConfiguration.Configure(WebApiConfig.Register);
 
Make sure you add it in the same order as shown below.
public class MvcApplication : System.Web.HttpApplication
{
    protected void Application_Start()
    {
        AreaRegistration.RegisterAllAreas();
        System.Web.Http.GlobalConfiguration.Configure(WebApiConfig.Register);
        RouteConfig.RegisterRoutes(RouteTable.Routes);
    }
}
 
The next step is to code the Web API Controller. The Web API Controller consists of a method named GetCustomers which accepts an object of CustomerModel.
The records of the Customers are fetched using Entity Framework and are filtered using the StartsWith function based on the value of the Name property.
Finally the records are returned as Generic List Collection.
This method is decorated with Route attribute which defines its Route for calling the Web API method and HttpPost attribute which signifies that the method will accept Http Post requests.
public class CustomerAPIController : ApiController
{
    [Route("api/CustomerAPI/GetCustomers")]
    [HttpPost]
    public List<Customer> GetCustomers(CustomerModel customer)
    {
        NorthwindEntities entities = new NorthwindEntities();
        return (from c in entities.Customers.Take(10)
                where c.ContactName.StartsWith(customer.Name) || string.IsNullOrEmpty(customer.Name)
                select c).ToList();
    }
}
 
 
Now take a Webform

HTML Markup
The following HTML Markup of the Web Form consists of an ASP.Net TextBox, a Button and a GridView.
Name:
<asp:TextBox ID="txtName" runat="server"></asp:TextBox>
<asp:Button ID="btnSearch" runat="server" Text="Search" OnClick="Search"/>
<hr/>
<asp:GridView ID="gvCustomers" runat="server" AutoGenerateColumns="false">
    <Columns>
        <asp:BoundField ItemStyle-Width="150px" DataField="CustomerID" HeaderText="CustomerID"/>
        <asp:BoundField ItemStyle-Width="150px" DataField="ContactName" HeaderText="Contact Name"/>
        <asp:BoundField ItemStyle-Width="150px" DataField="City" HeaderText="City"/>
    </Columns>
</asp:GridView>
 
 
Namespaces
You will need to import the following namespaces.
using System.Net;
using System.Text;
using System.Web.Script.Serialization;
 
 
Calling the Web API using WebClient class and populating the GridView
The PopulateGridView method is called inside the Page Load event handler and on the Click event handler of the Search button.
Inside the PopulateGridView method, the value of the Name TextBox is wrapped into a JSON object which is then serialized into a JSON string.
The URL of the Web API along with its Controller method and the serialized JSON string is passed to the UploadString method of the WebClient class.
The UploadString method of the WebClient class calls the Web API’s Controller method i.e. the GetCustomers method and returns the JSON string which is then de-serialized to Generic List of Customer class objects.
Finally the Generic List of Customer class objects is used to populate the GridView.
public partial class Default : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
        if (!this.IsPostBack)
        {
            this.PopulateGridView();
        }
    }
 
    protected void Search(object sender, EventArgs e)
    {
        this.PopulateGridView();
    }
 
    private void PopulateGridView()
    {
        string apiUrl = "http://localhost:26404/api/CustomerAPI";
        object input = new
        {
            Name = txtName.Text.Trim(),
        };
        string inputJson = (new JavaScriptSerializer()).Serialize(input);
        WebClient client = new WebClient();
        client.Headers["Content-type"] = "application/json";
        client.Encoding = Encoding.UTF8;
        string json = client.UploadString(apiUrl + "/GetCustomers", inputJson);
 
        gvCustomers.DataSource = (new JavaScriptSerializer()).Deserialize<List<Customer>>(json);
        gvCustomers.DataBind();
    }
 
    public class Customer
    {
        public string CustomerID { get; set; }
        public string ContactName { get; set; }
        public string City { get; set; }
    }
}


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