reference not set to an instance of an object

I'm new member .I want to ask about this exception which appears to me in datagridview column
ins.DeliveryNoteNo = dgv_Instalment.Rows[i].Cells["DeliveryNote"].Value.ToString();
but I ensure that I enter data to it
exception details
System.NullReferenceException was unhandled
Message="Object reference not set to an instance of an object."
Source="Nursing"
StackTrace:
       at Nursing.student_data.btn_edit_Click(Object sender, EventArgs e) in F:\New Folder\Visual Studio 2008\Projects\Nursing\Nursing\student_data.cs:line 628
       at System.Windows.Forms.Control.OnClick(EventArgs e)
       at System.Windows.Forms.Button.OnClick(EventArgs e)
       at System.Windows.Forms.Button.OnMouseUp(MouseEventArgs mevent)
       at System.Windows.Forms.Control.WmMouseUp(Message& m, MouseButtons button, Int32 clicks)
       at System.Windows.Forms.Control.WndProc(Message& m)
       at System.Windows.Forms.ButtonBase.WndProc(Message& m)
       at System.Windows.Forms.Button.WndProc(Message& m)
       at System.Windows.Forms.Control.ControlNativeWindow.OnMessage(Message& m)
       at System.Windows.Forms.Control.ControlNativeWindow.WndProc(Message& m)
       at System.Windows.Forms.NativeWindow.DebuggableCallback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam)
       at System.Windows.Forms.UnsafeNativeMethods.DispatchMessageW(MSG& msg)
       at System.Windows.Forms.Application.ComponentManager.System.Windows.Forms.UnsafeNativeMethods.IMsoComponentManager.FPushMessageLoop(Int32 dwComponentID, Int32 reason, Int32 pvLoopData)
       at System.Windows.Forms.Application.ThreadContext.RunMessageLoopInner(Int32 reason, ApplicationContext context)
       at System.Windows.Forms.Application.ThreadContext.RunMessageLoop(Int32 reason, ApplicationContext context)
       at System.Windows.Forms.Application.Run(Form mainForm)
       at Nursing.Program.Main() in F:\New Folder\Visual Studio 2008\Projects\Nursing\Nursing\Program.cs:line 18
       at System.AppDomain._nExecuteAssembly(Assembly assembly, String[] args)
       at System.AppDomain.ExecuteAssembly(String assemblyFile, Evidence assemblySecurity, String[] args)
       at Microsoft.VisualStudio.HostingProcess.HostProc.RunUsersAssembly()
       at System.Threading.ThreadHelper.ThreadStart_Context(Object state)
       at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
       at System.Threading.ThreadHelper.ThreadStart()
InnerException:

The first ting to do is to not assume. You assume there is a value but you need to verify that assumption; there are so many things that can be a problem that we cannot assume that things work even when we don't know any reason for it to not work.

The next thing to do is to determine what is null. You can do that by putting a breakpoint in the catch block; are you using try and catch? Do you know how to use a breakpoint? You can then hover your mouse over the various itmes to determine what is null. The problem could be any of the following:

dgv_Instalment
Rows[i]
Cells["DeliveryNote"]
Value

After determining which one of the above is null, then you can proceed to diagnose that specific problem.

2 Replies

Know the answer? Post it — somebody with the same question will find it here.

Gaurish Kumar17y ago
Hi

That error is coming due to the value of this
dgv_Instalment.Rows[i].Cells["DeliveryNote"].Value.ToString()

Value would be null.

Put a breakpoint and check the value of this.

0
Sam Hobbs17y ago
The first ting to do is to not assume. You assume there is a value but you need to verify that assumption; there are so many things that can be a problem that we cannot assume that things work even when we don't know any reason for it to not work.

The next thing to do is to determine what is null. You can do that by putting a breakpoint in the catch block; are you using try and catch? Do you know how to use a breakpoint? You can then hover your mouse over the various itmes to determine what is null. The problem could be any of the following:
- dgv_Instalment
- Rows[i]
- Cells["DeliveryNote"]
- Value
After determining which one of the above is null, then you can proceed to diagnose that specific problem.
0