In this article I will explain with an example, how to call (consume) MVC Web API in Windows Forms (WinForms) Application using C#.
The Web API 2 Controller method will fetch records from database using Entity Framework in ASP.Net MVC.
The Web API 2 Controller method will be called using WebClient class in Windows Forms Application to populate DataGridView control.
 
 

Database

Here I am making use of Microsoft’s Northwind Database. You can download it from here.
Download and install Northwind Database
 
 

Entity Framework Model

Once the Entity Framework is configured and connected to the database table, the Model will look as shown below.
Note: For beginners in ASP.Net MVC and Entity Framework, please refer my article ASP.Net MVC: Simple Entity Framework Tutorial with example.
 
Call (Consume) Web API in Windows Forms Application using C#
 
 

Model

The Model class consists of following properties.
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.
Now from the Add Scaffold window, choose the Web API 2 Controller – Empty option as shown below.
Call (Consume) Web API in Windows Forms Application using C#
 
Then give it a suitable name and click OK.
Call (Consume) Web API in Windows Forms Application using C#
 
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();
    }
}
 
 

Form Design

The Form consists of a TextBox, a Button and a DataGridView control.
Call (Consume) Web API in Windows Forms Application using C#
 
 

Namespaces

You will need to import the following namespaces.
using System.Net;
using System.Text;
using System.Web.Script.Serialization;
 
Note: In order to use the System.Web.Script.Serialization namespace, you will need to add reference of System.Web.Extensions assembly to your project, for more details refer here.
 
 

Calling the Web API using WebClient class and populating the DataGridView

Here, PopulateDataGridView method is called inside the Form Load event handler and on the Click event handler of the Search button.
Inside the PopulateDataGridView 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 DataGridView.
private void Form1_Load(object sender, EventArgs e)
{
    this.PopulateDataGridView();
}
 
private void btnSearch_Click(object sender, EventArgs e)
{
    this.PopulateDataGridView();
}
 
private void PopulateDataGridView()
{
    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);
 
    dataGridView1.DataSource = (new JavaScriptSerializer()).Deserialize<List<Customer>>(json);
}
}
 
public class Customer
{
    public string CustomerID { get; set; }
    public string ContactName { get; set; }
    public string City { get; set; }
}
 
 

Screenshot

Call (Consume) Web API in Windows Forms Application using C#
 
 

Downloads

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