[Solved] Get Property returns Null Reference Exception in ASP.Net

Hi ramco1917,

Please refer below sample.

HTML

<asp:Label ID="lblMessage" runat="server" />

Namespaces

C#

using System.Text;
using System.Collections.Generic;

VB.Net

Imports System.Collections.Generic
Imports System.Text

Code

C#

protected void Page_Load(object sender, EventArgs e)
{
    List<Training> Result = new List<Training>();
    Result.Add(new Training
    {
        TrainingID = 1,
        EmpName = "Test 1",
        TrainingNumber = "123",
        TrainingTypeMaster = new TrainingType { Description = "ASP.Net" }
    });

    Result.Add(new Training
    {
        TrainingID = 2,
        EmpName = "Test 2",
        TrainingNumber = "125",
        LocationMaster = new Location { LocationName = "Mumbai" }
    });

    StringBuilder htmlTable = new StringBuilder();
    htmlTable.Append("<table>");
    foreach (var colum in Result)
    {
        string EmpName = colum.EmpName;
        htmlTable.Append("<tr>");
        htmlTable.Append("<td style='display:none'>" + colum.TrainingID + "</td>");
        htmlTable.Append("<td>" + colum.TrainingNumber + "</td>");
        if (colum.TrainingTypeMaster != null)
        {
            htmlTable.Append(colum.TrainingTypeMaster.Description != null ? "<td>" + colum.TrainingTypeMaster.Description + "</td>" : "<td></td>");
        }
        else
        {
            htmlTable.Append("<td></td>");
        }
        if (colum.LocationMaster != null)
        {
            htmlTable.Append(colum.LocationMaster.LocationName != null ? "<td>" + colum.LocationMaster.LocationName : "</td>" + "<td></td>");
        }
        else
        {
            htmlTable.Append("<td></td>");
        }
        htmlTable.Append("<td>" + EmpName + "</td>");
        htmlTable.Append("<td class='text-center'><a id='btnEdit' style='cursor:pointer;' class='list-icons-item text-primary-600' title='Edit' href='NewTraining.aspx?val=" + colum.TrainingID + "'><i class='fas fa-pencil'></i> </a>" + "</td>");
        htmlTable.Append("</tr>");
    }
    htmlTable.Append("</table>");
    lblMessage.Text = htmlTable.ToString();
}

public class Training
{
    public int TrainingID { get; set; }
    public string EmpName { get; set; }
    public string TrainingNumber { get; set; }
    public TrainingType TrainingTypeMaster { get; set; }
    public Location LocationMaster { get; set; }
}

public class TrainingType
{
    public string Description { get; set; }
}

public class Location
{
    public string LocationName { get; set; }
}

VB.Net

Protected Sub Page_Load(ByVal sender As Object, ByVal e As EventArgs) Handles Me.Load
    Dim Result As List(Of Training) = New List(Of Training)()
    Result.Add(New Training With {
        .TrainingID = 1,
        .EmpName = "Test 1",
        .TrainingNumber = "123",
        .TrainingTypeMaster = New TrainingType With {
        .Description = "ASP.Net"
        }
    })

    Result.Add(New Training With {
               .TrainingID = 2,
               .EmpName = "Test 2",
               .TrainingNumber = "125",
               .LocationMaster = New Location With {
               .LocationName = "Mumbai"
               }
           })

    Dim htmlTable As StringBuilder = New StringBuilder()
    htmlTable.Append("<table>")

    For Each colum In Result
        Dim EmpName As String = colum.EmpName
        htmlTable.Append("<tr>")
        htmlTable.Append("<td style='display:none'>" & colum.TrainingID & "</td>")
        htmlTable.Append("<td>" & colum.TrainingNumber & "</td>")

        If colum.TrainingTypeMaster IsNot Nothing Then
            htmlTable.Append(If(colum.TrainingTypeMaster.Description IsNot Nothing, "<td>" & colum.TrainingTypeMaster.Description & "</td>", "<td></td>"))
        Else
            htmlTable.Append("<td></td>")
        End If
        If colum.LocationMaster IsNot Nothing Then
            htmlTable.Append(If(colum.LocationMaster.LocationName IsNot Nothing, "<td>" & colum.LocationMaster.LocationName, "</td>" & "<td></td>"))
        Else
            htmlTable.Append("<td></td>")
        End If
        htmlTable.Append("<td>" & EmpName & "</td>")
        htmlTable.Append("<td class='text-center'><a id='btnEdit' style='cursor:pointer;' class='list-icons-item text-primary-600' title='Edit' href='NewTraining.aspx?val=" & colum.TrainingID & "'><i class='fas fa-pencil'></i> </a>" & "</td>")
        htmlTable.Append("</tr>")
    Next
    htmlTable.Append("</table>")
    lblMessage.Text = htmlTable.ToString()
End Sub

Public Class Training
    Public Property TrainingID As Integer
    Public Property EmpName As String
    Public Property TrainingNumber As String
    Public Property TrainingTypeMaster As TrainingType
    Public Property LocationMaster As Location
End Class

Public Class TrainingType
    Public Property Description As String
End Class

Public Class Location
    Public Property LocationName As String
End Class

Screenshot