Error 'Object reference not set to an instance of an object.'

Question

Does anyone know where is my code going wrong here? This piece of code work perfectly fine but I transferred the file to another computer, this error popped out when I compile the file.

 private void ShowGeneratedSchedule(string sLocationName, string sAllocationDate)
    {
        //lstAllocation = db.allocations.Where(a => a.AllocationDate == sAllocationDate &&
        //    a.LocationName == sLocationName).ToList();

        scheduleDGV.EditMode = DataGridViewEditMode.EditProgrammatically;
        for (int i = 0; i < lstAllocation.Count; i++)
        {
            for (int j = 0; j < scheduleDGV.Rows.Count - 1; j++)
            {
                for (int k = 0; k < scheduleDGV.Columns.Count; k++)
                {
                    if (scheduleDGV[0, j].Value.Equals(lstAllocation[i].LocationName) &&
                        scheduleDGV[1, j].Value.Equals(lstAllocation[i].StationName) &&
                        scheduleDGV.Columns[k].HeaderText.Equals(lstAllocation[i].AllocationTime.ToString()))
                    {
                        if (lstAllocation[i].EmployeeName != null)
                        {
                            scheduleDGV[k, j].Value = lstAllocation[i].EmployeeName;
                        }
                    }
                }
            }
        }

        //scheduleDGV.DataSource = lstEmployeeSlot;
    }

The error is displayed when it reaches this line,

for (int i = 0; i < lstAllocation.Count; i++)

Does anyone know what's wrong here? Is it possible that it is transferred into another computer?

Answer 1

This, most likely, means that lstAllocation is null and was never assigned a value. Why this line is commented out?

 //lstAllocation = db.allocations.Where(a => a.AllocationDate == sAllocationDate &&
        //    a.LocationName == sLocationName).ToList();

Answer 2

lstAllocation is not initialized? What is it with the comment in the first line of the method? Why is that commented out? Without that lstAllocation has no content.

Answer 3

Looks like you have the line commented out where you assign lstAllocation to something. This is most likely your problem.

Answer 4

The lstAllocation reference variable is initialized with null (or an object is not constructed yet or an object is missing ) somewhere within the program/code.

It will be good practice to check the value of reference variable - whether it has null or reference of an object.

private void ShowGeneratedSchedule(string sLocationName, string sAllocationDate)
    {
        if(lstAllocation==null){
           Console.WriteLine("List is not initialized. Can't proceed");
           return;
        }
        //rest code
    }