Object reference not set to and instance of an object

Question

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this is my code to display data on screen during form load.

VB

SqlQuery = "Select * from Ledgers"
Sqlcommand = New MySqlCommand(SqlQuery, Conn)
count = Sqlcommand.ExecuteScalar
Da.SelectCommand = Sqlcommand
Da.Fill(Ds, "LEDG")
CmbFind.DataSource = Ds.Tables("LEDG")
CmbFind.ValueMember = "Name"
CmbFind.DisplayMember = "Name"
Rc = Ds.Tables("LEDG").Rows.Count
Rc = Rc - 1
TxtName.Text = Ds.Tables("LEDG").Rows(Rc)("Name")
CmbGrp.Text = Ds.Tables("LEDG").Rows(Rc)("Grp")
TxtAdd1.Text = Ds.Tables("LEDG").Rows(Rc)("Add1")
TxtAdd2.Text = Ds.Tables("LEDG").Rows(Rc)("Add2")
CmbCity.Text = Ds.Tables("LEDG").Rows(Rc)("City")
TxtDist.Text = Ds.Tables("LEDG").Rows(Rc)("Dist")
TxtPIN.Text = Ds.Tables("LEDG").Rows(Rc)("pincode")
DBState.Text = Ds.Tables("LEDG").Rows(Rc)("state")
TxtEmail.Text = Ds.Tables("LEDG").Rows(Rc)("email")
TxtPhone.Text = Ds.Tables("LEDG").Rows(Rc)("Landline")
TxtMob.Text = Ds.Tables("LEDG").Rows(Rc)("Mobile")
TxtVAT.Text = Ds.Tables("LEDG").Rows(Rc)("VATNO")
TxtCST.Text = Ds.Tables("LEDG").Rows(Rc)("CSTNO")
TxtGST.Text = Ds.Tables("LEDG").Rows(Rc)("GSTNO")
TxtPAN.Text = Ds.Tables("LEDG").Rows(Rc)("PAN")
If Not IsDBNull(Ds.Tables("LEDG").Rows(Rc)("OpBal")) Then
    TxtOpBal.Text = Ds.Tables("LEDG").Rows(Rc)("OpBal")
End If
If Not IsDBNull(Ds.Tables("LEDG").Rows(Rc)("BalType")) Then
    DbcDrCr.Text = Ds.Tables("LEDG").Rows(Rc)("BalType")
End If
Da.Dispose()

it works ok if I run it during form load directly, but if I create a function as

VB

Public Sub fieldDisp()
        Try

            SqlQuery = "Select * from Ledgers"
            Sqlcommand = New MySqlCommand(SqlQuery, Conn)
            count = Sqlcommand.ExecuteScalar
            Da.SelectCommand = Sqlcommand
            Da.Fill(Ds, "LEDG")
            FrmAccMast.CmbFind.DataSource = Ds.Tables("LEDG")
            FrmAccMast.CmbFind.ValueMember = "Name"
            FrmAccMast.CmbFind.DisplayMember = "Name"
            Rc = Ds.Tables("LEDG").Rows.Count
            Rc = Rc - 2
            FrmAccMast.TxtName.Text = Ds.Tables("LEDG").Rows(Rc)("Name")
            FrmAccMast.CmbGrp.Text = Ds.Tables("LEDG").Rows(Rc)("Grp")
            FrmAccMast.TxtAdd1.Text = Ds.Tables("LEDG").Rows(Rc)("Add1")
            FrmAccMast.TxtAdd2.Text = Ds.Tables("LEDG").Rows(Rc)("Add2")
            FrmAccMast.CmbCity.Text = Ds.Tables("LEDG").Rows(Rc)("City")
            FrmAccMast.TxtDist.Text = Ds.Tables("LEDG").Rows(Rc)("Dist")
            FrmAccMast.TxtPIN.Text = Ds.Tables("LEDG").Rows(Rc)("pincode")
            FrmAccMast.DBState.Text = Ds.Tables("LEDG").Rows(Rc)("state")
            FrmAccMast.TxtEmail.Text = Ds.Tables("LEDG").Rows(Rc)("email")
            FrmAccMast.TxtPhone.Text = Ds.Tables("LEDG").Rows(Rc)("Landline")
            FrmAccMast.TxtMob.Text = Ds.Tables("LEDG").Rows(Rc)("Mobile")
            FrmAccMast.TxtVAT.Text = Ds.Tables("LEDG").Rows(Rc)("VATNO")
            FrmAccMast.TxtCST.Text = Ds.Tables("LEDG").Rows(Rc)("CSTNO")
            FrmAccMast.TxtGST.Text = Ds.Tables("LEDG").Rows(Rc)("GSTNO")
            FrmAccMast.TxtPAN.Text = Ds.Tables("LEDG").Rows(Rc)("PAN")
            FrmAccMast.TxtOpBal.Text = Ds.Tables("LEDG").Rows(Rc)("OpBal")
            FrmAccMast.DbcDrCr.Text = Ds.Tables("LEDG").Rows(Rc)("BalType")
            Da.Dispose()

        Catch ex As Exception
            MessageBox.Show(ex.Message)
        End Try
    End Sub

and call this funcion during form load by
FieldDisp()

it returns error message
OBJECT REFERENCE NOT SET TO AND INSTANCE OF AN OBJECT.

Please Help.

What I have tried:

New to programming ,hence tried nothing much.

Posted 26-Aug-19 5:17am

Member 13550326

Updated 26-Aug-19 8:34am

Patrice T

v2

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Richard Deeming 27-Aug-19 14:11pm

Are you trying to call the function from the form's Load event? Or are you trying to call it from the constructor?

If you're trying to call it from the constructor, then you need to make sure you call InitializeComponent() first. That's the method which creates all of the controls on your form.

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Richard MacCutchan · Answer 1 · 2019-08-26T05:33:00

Solution 1

Use the debugger to see which line raises the error message. You can then investigate why that object reference is null.

Posted 26-Aug-19 5:33am

Richard MacCutchan

OriginalGriff · Answer 2 · 2019-08-26T05:53:00

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!

Afzaal Ahmad Zeeshan · Answer 3 · 2019-08-26T06:47:00

The only best solution here is to execute the application in debug mode and run the code line-by-line to find which of the lines throughs this exception. Once you have figured that out, just create the instance for that type—Hint: use the new keyword.

Read this post of mine to learn more on this topic, What Is A Null Error in Code Execution[^].

Patrice T · Answer 4 · 2019-08-26T08:34:00

Quote:
it returns error message
OBJECT REFERENCE NOT SET TO AND INSTANCE OF AN OBJECT.

Thr error message also tells you the position of error, it is usually a great help, it narrow the search.
The error message tells you that something failed and where, the debugger will show you what have been done, and thus what is not as expected.

Your code do not behave the way you expect, or you don't understand why !

There is an almost universal solution: Run your code on debugger step by step, inspect variables.
The debugger is here to show you what your code is doing and your task is to compare with what it should do.
There is no magic in the debugger, it don't know what your code is supposed to do, it don't find bugs, it just help you to by showing you what is going on. When the code don't do what is expected, you are close to a bug.
To see what your code is doing: Just set a breakpoint and see your code performing, the debugger allow you to execute lines 1 by 1 and to inspect variables as it execute.

Debugger - Wikipedia, the free encyclopedia[^]

Mastering Debugging in Visual Studio 2010 - A Beginner's Guide[^]
Basic Debugging with Visual Studio 2010 - YouTube[^]

Visual Basic / Visual Studio Video Tutorial - Basic Debugging - YouTube[^]
Visual Basic .NET programming for Beginners - Breakpoints and Debugging Tools[^]

The debugger is here to only show you what your code is doing and your task is to compare with what it should do.

Object reference not set to and instance of an object

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