Object Reference is not set to an instance of an object

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VB

Private Sub Button2_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button2.Click
        con.ConnectionString = str
        con.Open()
        Dim cmd As New SqlCommand("Update emp Set Enm=@name,Desig=@desig,Dt=@dt,Adds=@add,EImg=@picture where Id=" & DataGridView1.CurrentRow.Cells(0).Value(), con)
        cmd.Parameters.AddWithValue("@name", TextBox1.Text)
        cmd.Parameters.AddWithValue("@desig", TextBox2.Text)
        cmd.Parameters.AddWithValue("@dt", TextBox3.Text)
        cmd.Parameters.AddWithValue("@add", TextBox4.Text)
        Dim arrImage() As Byte
        Dim myMs As New IO.MemoryStream
        Me.PictureBox1.Image.Save(myMs, Me.PictureBox1.Image.RawFormat)//Here Error Shows//
        arrImage = myMs.GetBuffer
        cmd.Parameters.Add(New SqlParameter("@picture", SqlDbType.Image)).Value = arrImage
        cmd.ExecuteNonQuery()
        MessageBox.Show("Updated has been saved", "Save", MessageBoxButtons.OK)
        con.Close()

Posted 4-Sep-15 2:37am

hspl

Updated 4-Sep-15 2:47am

F-ES Sitecore

v2

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Comments

ZurdoDev 4-Sep-15 8:46am

What is your question? Fix the error.

Richard Deeming 4-Sep-15 8:51am

Your code is vulnerable to SQL Injection[^].

NEVER use string concatenation to build a SQL query. ALWAYS use a parameterized query.

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Sergey Alexandrovich Kryukov · Answer 1 · 2015-09-04T05:53:00

It means that either PictureBox1 is null, if not, PictureBox1.Image is null.

It's good the you've shown the line where the exception was thrown, but it wasn't exact point in code.

Not to worry. This is one of the very easiest cases to detect and fix. It simply means that some member/variable of some reference type is dereferenced by using and of its instance (non-static) members, which requires this member/variable to be non-null, but in fact it appears to be null. Simply execute it under debugger, it will stop the execution where the exception is thrown. Put a break point on that line, restart the application and come to this point again. Evaluate all references involved in next line and see which one is null while it needs to be not null. After you figure this out, fix the code: either make sure the member/variable is properly initialized to a non-null reference, or check it for null and, in case of null, do something else.

Please see also: want to display next record on button click. but got an error in if condition of next record function "object reference not set to an instance of an object".

Sometimes, you cannot do it under debugger, by one or another reason. One really nasty case is when the problem is only manifested if software is built when debug information is not available. In this case, you have to use the harder way. First, you need to make sure that you never block propagation of exceptions by handling them silently (this is a crime of developers against themselves, yet very usual). The you need to catch absolutely all exceptions on the very top stack frame of each thread. You can do it if you handle the exceptions of the type System.Exception. In the handler, you need to log all the exception information, especially the System.Exception.StackTrace:
http://msdn.microsoft.com/en-us/library/system.exception.aspx,
http://msdn.microsoft.com/en-us/library/system.exception.stacktrace.aspx.

The stack trace is just a string showing the full path of exception propagation from the throw statement to the handler. By reading it, you can always find ends. For logging, it's the best (in most cases) to use the class System.Diagnostics.EventLog:
http://msdn.microsoft.com/en-us/library/system.diagnostics.eventlog.aspx.

Good luck,

—SA