Object reference not set to an instance of an object error in VB.NET

Question

1.00/5 (1 vote)

See more:

Hii..frds.my project have two registrations forms that are User registration and Staff Registration in vb.net and SQL server. The user registration form worked correctly. But Staff Registration have one error (" Object reference not set to an instance of an object "). I make both coding in similar logical. Both coding are logically similarly and I checked..But it shows the error...I already makes both forms in MS Access . That time Staff Registration form correctly.. Now, the same form using MS Access or SQL shows the same prb...but I want to need in SQL not ms access. I described this prb for your understanding. So I tell the ms access.. Now what can i do? Pls hell me frds....

What I have tried:

I need fix that prb..I need to worked form of staff registration...

Posted 18-Apr-18 19:48pm

Member 13738315

Updated 18-Apr-18 20:22pm

Add a Solution

1 solution

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 · 2018-04-18T20:23:00

Solution 1

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!

Posted 18-Apr-18 20:23pm

OriginalGriff

Comments

Member 13738315 19-Apr-18 3:03am

ok.. itry it... if you help me,,pls see my coding below...

Try

If Len(Trim(TextBox2.Text)) = 0 Then
MessageBox.Show("Please enter staff name", "Input Error", MessageBoxButtons.OK, MessageBoxIcon.Error)
TextBox2.Focus()
Exit Sub
End If
If RadioButton1.Checked = False And RadioButton2.Checked = False Then
MessageBox.Show("Please select gender", "Input Error", MessageBoxButtons.OK, MessageBoxIcon.Error)
Exit Sub
Exit Sub
End If
If Len(Trim(TextBox3.Text)) = 0 Then
MessageBox.Show("Please enter father's name", "Input Error", MessageBoxButtons.OK, MessageBoxIcon.Error)
TextBox3.Focus()
Exit Sub
End If
If Len(Trim(ComboBox1.Text)) = 0 Then
MessageBox.Show("Please select department", "Input Error", MessageBoxButtons.OK, MessageBoxIcon.Error)
ComboBox1.Focus()
Exit Sub
End If
If Len(Trim(TextBox5.Text)) = 0 Then
MessageBox.Show("Please enter temporary address", "Input Error", MessageBoxButtons.OK, MessageBoxIcon.Error)
TextBox5.Focus()
Exit Sub
End If
If Len(Trim(TextBox6.Text)) = 0 Then
MessageBox.Show("Please enter permanent address", "Input Error", MessageBoxButtons.OK, MessageBoxIcon.Error)
TextBox6.Focus()
Exit Sub
End If
If Len(Trim(TextBox8.Text)) = 0 Then
MessageBox.Show("Please enter mobile no.", "Input Error", MessageBoxButtons.OK, MessageBoxIcon.Error)
TextBox8.Focus()
Exit Sub
End If
If RadioButton1.Checked = True Then
Gender = RadioButton1.Text
End If
If RadioButton2.Checked = True Then
Gender = RadioButton2.Text
End If
conn = New SqlConnection(Connstring)
conn.Open()

sqlstring = "insert into Staff([Staff Id], [Staff Name}, [Father Name],DateOfJoining, Department, [Temporary Address], [Permanent Address], DOB, [Phone No], [Mobile No], [Email Id], Photo,Gender) VALUES('" & TextBox1.Text & "','" & TextBox2.Text & "','" & TextBox3.Text & "',#" & DateTimePicker1.Text & "#,'" & ComboBox1.Text & "','" & TextBox5.Text & "','" & TextBox6.Text & "','" & DateTimePicker2.Text & "','" & TextBox7.Text & "','" & TextBox8.Text & "','" & TextBox9.Text & "',@image,'" & Gender & "'"
cmd = New SqlCommand(sqlstring, conn)

cmd.Connection = conn
Dim ms As New MemoryStream()
Dim bmpImage As New Bitmap(PictureBox1.Image)
bmpImage.Save(ms, System.Drawing.Imaging.ImageFormat.Jpeg)
Dim data As Byte() = ms.GetBuffer()
Dim p As New SqlParameter("@image", SqlDbType.VarBinary)
p.Value = data
cmd.Parameters.Add(p)
cmd.ExecuteNonQuery()
cmd.Dispose()
conn.Close()

MessageBox.Show("Successfully saved", " Staff Record", MessageBoxButtons.OK, MessageBoxIcon.Information)
Button3.Enabled = False
Catch ex As Exception
MessageBox.Show(ex.Message, "Error", MessageBoxButtons.OK, MessageBoxIcon.Error)
End Try

OriginalGriff 19-Apr-18 3:29am

I do wish you hadn't shown me that...

You have worse problems than you think. Do not do databases like that!
Never concatenate strings to build a SQL command. It leaves you wide open to accidental or deliberate SQL Injection attack which can destroy your entire database. Use Parametrized queries instead.

When you concatenate strings, you cause problems because SQL receives commands like:

SELECT * FROM MyTable WHERE StreetAddress = 'Baker's Wood'

The quote the user added terminates the string as far as SQL is concerned and you get problems. But it could be worse. If I come along and type this instead: "x';DROP TABLE MyTable;--" Then SQL receives a very different command:

SELECT * FROM MyTable WHERE StreetAddress = 'x';DROP TABLE MyTable;--'

Which SQL sees as three separate commands:

SELECT * FROM MyTable WHERE StreetAddress = 'x';

A perfectly valid SELECT

DROP TABLE MyTable;

A perfectly valid "delete the table" command

--'

And everything else is a comment.
So it does: selects any matching rows, deletes the table from the DB, and ignores anything else.

So ALWAYS use parameterized queries! Or be prepared to restore your DB from backup frequently. You do take backups regularly, don't you?

When you have gone through your whole app and fixed every single database access then you can start looking at your null reference - which as I said, we can't do for you!