How to add the stock quantity but that erase the total stock quantity any help!

[hannoudw]

hi i have a form that contain 2 text box (article and qty) and a next button .
when i click on the button a new form will open in datasheet view, contain 5 text box ( size, quantity, reference, article, qty_to_add).
i want when i change the qty_to_add to modify the stock quantity (quantity in the second form).
so i wrote this :

 Private Sub Add_AfterUpdate()
Me.Qty.Value = Me.Qty.Value - Me.qty_to_Add.OldValue
DoCmd.DoMenuItem acFormBar, acRecordsMenu, 5, , acMenuVer70
Me.Qty.Value = Me.Qty.Value + Me.qty_to_Add.Value
End Sub

and it work fine but the problem is that sometime the quantity.value is null and when i modify the qty_to_add the stock quantity became null.
Any help please...

[beacon]

Hi hannoudw,

Try adding an If...Then statement that checks to see if the quantity is null before you start your other calculations.

Private Sub Add_AfterUpdate()
    
    If Not IsNull(Me.Qty.Value) Then
        Me.Qty.Value = Me.Qty.Value - Me.qty_to_Add.OldValue
        DoCmd.DoMenuItem acFormBar, acRecordsMenu, 5, , acMenuVer70
        Me.Qty.Value = Me.Qty.Value + Me.qty_to_Add.Value
    Else
        'Display a message to the user to enter a quantity
        MsgBox "Please enter a value in the quantity field.", vbExclamation + VBOKOnly, "Null Quantity"
        'Put the cursor in the Qty field so the user can enter a value
        Me.Qty.SetFocus
    End If

End Sub

[missinglinq]

You can use the Nz() function to change a Null to Zero.

Me.Qty.Value = Nz(Me.Qty.Value , 0) + Me.qty_to_Add.V alue

Welcome to Bytes!

Linq ;0)>

[beacon]

You can use the Nz() function to change a Null to Zero.

Me.Qty.Value = Nz(Me.Qty.Value , 0) + Me.qty_to_Add.V alue

Welcome to Bytes!

Linq ;0)>

Completely forgot about Nz() Linq. I was addressing it from the perspective that null values weren't acceptable, so thanks for having my back.

[hannoudw]

Thanks @missinglinq
that solved the problem
now i'm trying to have a control over the total number that i added . therefore i added 2 text box on the header of the datasheet form. on of them have default value =[Forms]![Add Qty]![qtyTxt] (and that's the total quantity that i'm adding) and the other is equale of the sum of the qty_to_add (=sum[qty_to_add])
and it's not working...
olso i tried to add a button in the header and i wrote this code :

Private Sub Command22_Click()
If Me.sum.Value <> Me.q.Value Then
MsgBox ("check the adding numbers")
End If
End Sub

and still not working ... any help please