How can I fix the error: System.NullReferenceException: 'Object reference not set to an instance of an object.'

Question

The following is my code:

namespace RegistrationForm  
{  
    public partial class Rent : Form  
    {  
        AptId aptId;  
        Payment payment;  
        public Rent(AptId apt)  
        {  
            InitializeComponent();  
            this.aptId = apt;  
              
        }  
  
        public Rent(Payment pay)  
        {  
            InitializeComponent();  
            this.payment = pay;  
        }  
  
        private void Rent_Load(object sender, EventArgs e)  
        {  
            rentTextBox.Text = aptId.rentTextBox.Text;  
            rentTextBox.Text = payment.rentTextBox.Text;  
        }  
        private void button1_Click(object sender, EventArgs e)  
        {  
            DateTime current = DateTime.Now;  
            MessageBox.Show("Your transaction on " + current.ToString() + " of BHD " + rentTextBox.Text + " was successful!!!");  
  
            this.Close();  
        }  
  
          
    }  
}  

I am getting error on this statement: rentTextBox.Text = aptId.rentTextBox.Text;

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

Doesn't make sense to me cause the statement under it is the same just a different name and different table referencing name, but it doesn't show any such error.

I would really appreciate if my error is solved in any way.

Thanks in advance

Answer 1

in the line:

rentTextBox.Text = aptId.rentTextBox.Text;

the error means one of the objects is null (aptId) in this case. you have a basic logic error. the code:

         private void Rent_Load(object sender, EventArgs e)  
         {  
             rentTextBox.Text = aptId.rentTextBox.Text;  
             rentTextBox.Text = payment.rentTextBox.Text;  
         }  

assume both aptId and payment are defined, but no code path does this. Your constructors only initial one of them, so no matter which constructor you call. as you are writing to the same field you only wanted to execute one f the statements:

             private void Rent_Load(object sender, EventArgs e)  
             {  
                 if (aptId != null)  
                     rentTextBox.Text = aptId.rentTextBox.Text;  
                 else if (payment != null)  
                     rentTextBox.Text = payment.rentTextBox.Text;  
                 else  
                     rentTextBox.Text = "constructor called with null value";  
             }  

Answer 2

Add null value check to your Rent_load():

private void Rent_Load(object sender, EventArgs e)  
{  
	if(aptId != null && aptId.rentTextBox != null)  
	{  
		rentTextBox.Text = aptId.rentTextBox.Text;  
	}  
	if(aptId != null && payment.rentTextBox != null)  
	{  
		rentTextBox.Text = payment.rentTextBox.Text;  
	}  
}  
  

If right,please Accept.
Enjoy programming!!!