[Solved] Passing parameter to ASP.Net Web API Controller Value are always null

Hi makumbi,

Check this example. Now please take its reference and correct your code.

Database

For this example I have used of Northwind database that you can download using the link given below.

Download Northwind Database

HTML

Name: <asp:TextBox ID="txtName" runat="server"></asp:TextBox>
<br />
Country: <asp:TextBox ID="txtCountry" runat="server"></asp:TextBox>
<br />
<asp:Button ID="btnSearch" runat="server" Text="Search" OnClick="Search" />
<hr />
<asp:GridView ID="gvCustomers" runat="server" AutoGenerateColumns="false">
    <Columns>
        <asp:BoundField DataField="CustomerID" HeaderText="CustomerID" />
        <asp:BoundField DataField="ContactName" HeaderText="ContactName" />
        <asp:BoundField DataField="City" HeaderText="City" />
    </Columns>
</asp:GridView>

Model

Public Class CustomerModel
    Public Property Name As String
    Public Property Country As String
End Class

Namespaces

Imports System.Configuration
Imports System.Data.SqlClient
Imports System.Web.Http
Imports System.Net
Imports System.Web.Script.Serialization

Controller

Public Class CustomerAPIController
    Inherits ApiController
    <Route("api/CustomerAPI/GetCustomers")>
    <HttpPost>
    Public Function GetCustomers(customer As CustomerModel) As List(Of Customer)
        Dim customers As New List(Of Customer)()
        Dim constr As String = ConfigurationManager.ConnectionStrings("conString").ConnectionString
        Using con As New SqlConnection(constr)
            Dim query As String = "SELECT CustomerID,ContactName,City,Country FROM Customers WHERE (ContactName LIKE @Name + '%' OR @Name IS NULL) AND (Country = @Country OR @Country IS NULL)"
            Using cmd As New SqlCommand(query)
                cmd.Connection = con
                cmd.Parameters.AddWithValue("@Name", customer.Name)
                cmd.Parameters.AddWithValue("@Country", customer.Country)
                con.Open()
                Using sdr As SqlDataReader = cmd.ExecuteReader()
                    While sdr.Read()
                        customers.Add(New Customer() With {
                            .CustomerID = sdr("CustomerID").ToString(),
                            .ContactName = sdr("ContactName").ToString(),
                            .City = sdr("City").ToString(),
                            .Country = sdr("Country").ToString()
                        })
                    End While
                End Using
                con.Close()
            End Using
        End Using

        Return customers
    End Function
End Class

Code

Protected Sub Page_Load(ByVal sender As Object, ByVal e As EventArgs) Handles Me.Load
    If Not Me.IsPostBack Then
        Me.PopulateGridView()
    End If
End Sub

Protected Sub Search(ByVal sender As Object, ByVal e As EventArgs)
    Me.PopulateGridView()
End Sub

Private Sub PopulateGridView()
    Dim apiUrl As String = "http://localhost:61977/api/CustomerAPI"
    Dim input As Object = New With {
        .Name = txtName.Text.Trim(),
        .Country = txtCountry.Text.Trim()
    }
    Dim inputJson As String = New JavaScriptSerializer().Serialize(input)
    Dim client As WebClient = New WebClient()
    client.Headers("Content-type") = "application/json"
    client.Encoding = Encoding.UTF8
    Dim json As String = client.UploadString(apiUrl & "/GetCustomers", inputJson)
    gvCustomers.DataSource = (New JavaScriptSerializer()).Deserialize(Of List(Of Customer))(json)
    gvCustomers.DataBind()
End Sub

Public Class Customer
    Public Property CustomerID As String
    Public Property ContactName As String
    Public Property City As String
    Public Property Country As String
End Class

Screenshot