I am getting an error object set to instance of an object project link - https://drive.google.com/drive/folders/1nu7huhfjgowxc22aptlhlwienyth_lcx? Usp=sharing

Question

1.00/5 (1 vote)

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C#

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;
using FireSharp.Config;
using FireSharp.Response;
using FireSharp.Interfaces;

namespace vbEngC
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        IFirebaseConfig fcon = new FirebaseConfig()
        {
            AuthSecret = "NK4r2FbHGqMpmEPfPMgRkmaqOBjEzYeJYCvpmn0q",
            BasePath = "https://cfireeng-6efa8.firebaseio.com/"
        };

        IFirebaseClient client;

        private void Form1_Load(object sender, EventArgs e)
        {
            try 
            {
                client = new FireSharp.FirebaseClient(fcon);
            }
            catch
            {
                MessageBox.Show("there was problem in the internet.");
            }
        }

        private void InsertBtn_Click(object sender, EventArgs e)
        {
            #region store in the studentlist
            Student std = new Student()
            {
                FullName = nameTbox.Text,
                RollNo = rollTbox.Text,
                Grade = gradeTobx.Text,
                Section = secTbox.Text
            };
            var setter = client.Set("StudentList/"+rollTbox.Text,std);
            MessageBox.Show("data inserted successfully");
            #endregion

            //store in sno
            FirebaseResponse res = client.Get(@"Counter");
            int Counter = int.Parse(res.ResultAs<string>());

            MyRoll roll = new MyRoll()
            {
                RollNo = rollTbox.Text
            };

            var set2 = client.Set(@"Counter", ++Counter);
            var set3 = client.Set(@"Sno/" + Counter, roll);

            MessageBox.Show("INSERTED SUCCESSFULLY");
        }

        private void SelectBtn_Click(object sender, EventArgs e)
        {
            var result = client.Get("StudentList/" + rollTbox.Text);
            Student std = result.ResultAs<student>();
            nameTbox.Text = std.FullName;
            gradeTobx.Text = std.Grade;
            secTbox.Text = std.Section;
            MessageBox.Show("data retrieved successfully");
        }

        private void UpdateBtn_Click(object sender, EventArgs e)
        {
            Student std = new Student()
            {
                FullName = nameTbox.Text,
                RollNo = rollTbox.Text,
                Grade = gradeTobx.Text,
                Section = secTbox.Text
            };
            var setter = client.Update("StudentList/" + rollTbox.Text, std);
            MessageBox.Show("data inserted successfully");
        }

        private void DeleteBtn_Click(object sender, EventArgs e)
        {
            var result = client.Delete("StudentList/" + rollTbox.Text);
            MessageBox.Show("data deleted successfully");
        }

        //show all records
        private void button1_Click(object sender, EventArgs e)
        {
            DataTable dt = new DataTable();
            dt.Columns.Add("Full Name");
            dt.Columns.Add("Roll No");
            dt.Columns.Add("Grade");
            dt.Columns.Add("Section");

           
            FirebaseResponse res = client.Get(@"Counter");
            int Counter = int.Parse(res.ResultAs<string>());

            for (int i = 1; i <= Counter; i++)
            {
                FirebaseResponse res2 = client.Get(@"Sno/" + i + "/RollNo");
                string RollNo = res2.ResultAs<string>();

                var res3 = client.Get(@"StudentList/" + RollNo);
                Student std = res3.ResultAs<student>();

                if(1==1) // (std!=null)
                {
                    dt.Rows.Add(std.FullName, std.RollNo, std.Grade, std.Section);
                }
            }

            foreach (DataRow item in dt.Rows)
            {
                dataGridView1.Rows.Add(item.ItemArray);
            }
        }
    }
}

What I have tried:

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;
using FireSharp.Config;
using FireSharp.Response;
using FireSharp.Interfaces;

namespace vbEngC
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        IFirebaseConfig fcon = new FirebaseConfig()
        {
            AuthSecret = "NK4r2FbHGqMpmEPfPMgRkmaqOBjEzYeJYCvpmn0q",
            BasePath = "https://cfireeng-6efa8.firebaseio.com/"
        };

        IFirebaseClient client;

        private void Form1_Load(object sender, EventArgs e)
        {
            try 
            {
                client = new FireSharp.FirebaseClient(fcon);
            }
            catch
            {
                MessageBox.Show("there was problem in the internet.");
            }
        }

        private void InsertBtn_Click(object sender, EventArgs e)
        {
            #region store in the studentlist
            Student std = new Student()
            {
                FullName = nameTbox.Text,
                RollNo = rollTbox.Text,
                Grade = gradeTobx.Text,
                Section = secTbox.Text
            };
            var setter = client.Set("StudentList/"+rollTbox.Text,std);
            MessageBox.Show("data inserted successfully");
            #endregion

            //store in sno
            FirebaseResponse res = client.Get(@"Counter");
            int Counter = int.Parse(res.ResultAs<string>());

            MyRoll roll = new MyRoll()
            {
                RollNo = rollTbox.Text
            };

            var set2 = client.Set(@"Counter", ++Counter);
            var set3 = client.Set(@"Sno/" + Counter, roll);

            MessageBox.Show("INSERTED SUCCESSFULLY");
        }

        private void SelectBtn_Click(object sender, EventArgs e)
        {
            var result = client.Get("StudentList/" + rollTbox.Text);
            Student std = result.ResultAs<Student>();
            nameTbox.Text = std.FullName;
            gradeTobx.Text = std.Grade;
            secTbox.Text = std.Section;
            MessageBox.Show("data retrieved successfully");
        }

        private void UpdateBtn_Click(object sender, EventArgs e)
        {
            Student std = new Student()
            {
                FullName = nameTbox.Text,
                RollNo = rollTbox.Text,
                Grade = gradeTobx.Text,
                Section = secTbox.Text
            };
            var setter = client.Update("StudentList/" + rollTbox.Text, std);
            MessageBox.Show("data inserted successfully");
        }

        private void DeleteBtn_Click(object sender, EventArgs e)
        {
            var result = client.Delete("StudentList/" + rollTbox.Text);
            MessageBox.Show("data deleted successfully");
        }

        //show all records
        private void button1_Click(object sender, EventArgs e)
        {
            DataTable dt = new DataTable();
            dt.Columns.Add("Full Name");
            dt.Columns.Add("Roll No");
            dt.Columns.Add("Grade");
            dt.Columns.Add("Section");

           
            FirebaseResponse res = client.Get(@"Counter");
            int Counter = int.Parse(res.ResultAs<string>());

            for (int i = 1; i <= Counter; i++)
            {
                FirebaseResponse res2 = client.Get(@"Sno/" + i + "/RollNo");
                string RollNo = res2.ResultAs<string>();

                var res3 = client.Get(@"StudentList/" + RollNo);
                Student std = res3.ResultAs<Student>();

                if(1==1) // (std!=null)
                {
                    dt.Rows.Add(std.FullName, std.RollNo, std.Grade, std.Section);
                }
            }

            foreach (DataRow item in dt.Rows)
            {
                dataGridView1.Rows.Add(item.ItemArray);
            }
        }
    }
}

Posted 7-Aug-20 20:08pm

Infinite Coders

Updated 7-Aug-20 20:15pm

OriginalGriff

v2

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OriginalGriff · Accepted Answer · 2020-08-07T20:15:00

This is one of the most common problems we get asked, and it's also the one we are least equipped to answer, but you are most equipped to answer yourself.

Let me just explain what the error means: You have tried to use a variable, property, or a method return value but it contains null - which means that there is no instance of a class in the variable.
It's a bit like a pocket: you have a pocket in your shirt, which you use to hold a pen. If you reach into the pocket and find there isn't a pen there, you can't sign your name on a piece of paper - and you will get very funny looks if you try! The empty pocket is giving you a null value (no pen here!) so you can't do anything that you would normally do once you retrieved your pen. Why is it empty? That's the question - it may be that you forgot to pick up your pen when you left the house this morning, or possibly you left the pen in the pocket of yesterdays shirt when you took it off last night.

We can't tell, because we weren't there, and even more importantly, we can't even see your shirt, much less what is in the pocket!

Back to computers, and you have done the same thing, somehow - and we can't see your code, much less run it and find out what contains null when it shouldn't.
But you can - and Visual Studio will help you here. Run your program in the debugger and when it fails, VS will show you the line it found the problem on. You can then start looking at the various parts of it to see what value is null and start looking back through your code to find out why. So put a breakpoint at the beginning of the method containing the error line, and run your program from the start again. This time, VS will stop before the error, and let you examine what is going on by stepping through the code looking at your values.

But we can't do that - we don't have your code, we don't know how to use it if we did have it, we don't have your data. So try it - and see how much information you can find out!