Exception of type systemnullrefenceexception sqlserver on select

Question

1.00/5 (1 vote)

See more:

Hello, I have a problem with this C# code, Then the code below load value from table into database called Distinta, the function is call SetValoriDistinta, when i run this function, the compiler give to me the error of image. How can i solve this error?

<a href="https://imgur.com/a/gMyTd">IMAGE OF ERROR</a>

C#

<pre><pre>FIRST.CS

//Istanzio la distinta e configuro i parametri da passare all'oggetto distinta
Distinta d = new Distinta();
d.db = db;
d = new Distinta(CodiceDistinta);
//Carico dentro l'oggetto d i valori distinta
d.SetValoriDistinta();
//Setto la textbox con il codice della distinta
textBoxIdDistinta.Text = d.GetIdDistinta();
//Ridimensionamento Immagine
pictureBoxImmagineDistinta.SizeMode = PictureBoxSizeMode.StretchImage;
//TOGLIE RIGA VUOTA
dataGridViewComposizioneDistinta.AllowUserToAddRows = false;
//Caricamento valori distinta default
labelDataInserimento.Text = d.DataInserimento;
labelDataUltimaModifica.Text = d.DataModifica;
textBoxDescrizione.Text = d.Descrizione;
richTextBoxDescrizioneEstesa.Text = d.DescrizioneEstesa;
textBoxUnitadiMisura.Text = d.UM;
textBoxIdDistinta.Text = d.IdDistinta;
pictureBoxImmagineDistinta.Image = d.immagine;

Distinta.CS

 class Distinta
    {
        public int CodiceDistinta;
        public String NomeDistinta,IdDistinta, DataInserimento, DataModifica, Descrizione, DescrizioneEstesa, UM;
        public Database db;
        public Bitmap immagine;

        public Distinta(int CodiceDistinta)
        {
            this.CodiceDistinta = CodiceDistinta;
        }

        public Distinta()
        {
        }

        public String GetIdDistinta()
        {
            String IdDistinta=null;
            try
            {
                String query = "select * from Distinta Where CodiceDistinta=@CodiceDistinta ";
                SqlCommand command = new SqlCommand(query, db.apriconnessione());
                command.Parameters.Add("@CodiceDistinta", SqlDbType.Int).Value = CodiceDistinta;
                SqlDataAdapter da = new SqlDataAdapter(command);
                DataTable dt = new DataTable();
                da.Fill(dt);

                if (dt.Rows.Count > 0)
                {
                    foreach (DataRow dr in dt.Rows)
                    {
                        IdDistinta = dr["IdDistinta"].ToString();
                    }
                }

                db.chiudiconnessione();
            }

            catch (Exception ex)
            {

            }

      
            return IdDistinta;
        }

        public void SetValoriDistinta()
        {
            try
            {
                SqlConnection conn = db.apriconnessione();
                String query = "Select * from Distinta Where CodiceDistinta=@CodiceDistinta";
                SqlCommand command = new SqlCommand(query, conn);
                command.Parameters.Add("@CodiceDistinta", SqlDbType.Int).Value = CodiceDistinta;
                using (var reader = command.ExecuteReader()){

                        while (reader.Read())
                        {
                            DataInserimento = reader["DataInserimento"].ToString();
                            DataModifica = reader["DataModifica"].ToString();
                            Descrizione = reader["Descrizione"].ToString();
                            DescrizioneEstesa= reader["DescrizioneEstesa"].ToString();
                            UM = reader["UnitaMisura"].ToString();
                            IdDistinta= reader["IdDistinta"].ToString();

                            byte[] picData = reader["Images"] as byte[] ?? null;

                            if (picData != null)
                            {
                                using (MemoryStream ms = new MemoryStream(picData))
                                {
                                    immagine = new System.Drawing.Bitmap(ms);

                                }
                            }
                        }

                    }

                db.chiudiconnessione();
                conn.Close();                            
            }

            catch(Exception ex)
            {
               MessageBox.Show("Errore caricamento Immagine:  "+ex);

            }

        }

}

What I have tried:

Hello, I have a problem with this C# code, Then the code below load value from table into database called Distinta, the function is call SetValoriDistinta, when i run this function, the compiler give to me the error of image. How can i solve this error?

Posted 23-Oct-17 0:21am

rikidev

Updated 23-Oct-17 1:28am

Add a Solution

Comments

Karthik_Mahalingam 23-Oct-17 23:06pm

in which line you are getting this error ?

2 solutions

Add a Solution

Add your solution here

Treat my content as plain text, not as HTML

Preview 0

…

Existing Members

Sign in to your account

...or Join us

Download, Vote, Comment, Publish.

Your Email
Password
Forgot your password?

Your Email
This email is in use. Do you need your password?
Optional Password

I have read and agree to the Terms of Service and Privacy Policy
Please subscribe me to the CodeProject newsletters

When answering a question please:

Read the question carefully.
Understand that English isn't everyone's first language so be lenient of bad spelling and grammar.
If a question is poorly phrased then either ask for clarification, ignore it, or edit the question and fix the problem. Insults are not welcome.
Don't tell someone to read the manual. Chances are they have and don't get it. Provide an answer or move on to the next question.

Let's work to help developers, not make them feel stupid.

This content, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

OriginalGriff · Answer 1 · 2017-10-23T00:26:00

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!

PeejayAdams · Answer 2 · 2017-10-23T01:28:00

This looks wrong to me:

Distinta d = new Distinta();
d.db = db;
d = new Distinta(CodiceDistinta);

You create an instance of Distinta with the empty constructor.

You then set the database property of that instance.

You then replace that instance with a fresh one - losing the value of db which you then attempt to use in SetValoriDistinta():

SqlConnection conn = db.apriconnessione();

As far as I can see, db will be null here and cause the exception to be thrown.

Exception of type systemnullrefenceexception sqlserver on select

2 solutions

Solution 1

Solution 2

Add your solution here

Preview 0