Question

Checking Null Value in VB.NET

Asked by: BrijBhasin

I'm trying to check if one of my form controls has null value and have use
droplist.SelectedItem.text = null
droplist.SelectedItem.text is null
IsDBNull(dropList.SelectedItem.text)
but one of the above seem to work, can someone tell me how to check if it is null and assign it a value.

Brij

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Asked On
2003-09-16 at 13:39:45ID20740596
Tags

null

,

check

,

value

Topic

.NET

Participating Experts
4
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500
Comments
15

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Answers

 

by: mondayblueboyPosted on 2003-09-16 at 13:51:05ID: 9373440


Not sure what you want,

droplist.SelectedItem Is Null, means none of DropDownList item is selected
droplist.SelectedItem.Text = "", means the selected item has empty string

Hope this info would helps

 

by: mondayblueboyPosted on 2003-09-16 at 13:55:30ID: 9373472


Sorry in VB.NET should be,

If Not IsNothing(droplist)  Then

   If droplist.SelectedItem.Text.Equal("") Then

       ' assign its value
   
    End If

End If

 

by: BrijBhasinPosted on 2003-09-16 at 13:59:46ID: 9373497

it gives me an error saying - BC30456: 'Equal' is not a member of 'String'.

 

by: morphinexPosted on 2003-09-16 at 14:00:28ID: 9373500

Are you trying to check if one of the list item is null out of many ?  Like, say you've populated a listbox from a dataset and you want to check if you've inserted a null value somewhere in the middle?

If that's the case.. try --

Dim iInteger as Integer

For iInteger = 0 to dropList.Items.Count - 1
    if IsDbNull(dropList.Items.Item(iInteger)) then dropList.Items.Item(iInteger) = "0"
Next

 

by: malharonePosted on 2003-09-16 at 14:00:48ID: 9373502

use NOTHING
if (myObj is nothing) then exit sub

for DB NULLs .. if isdbnull(myDataRow("clientName")) then exit sub

 

by: morphinexPosted on 2003-09-16 at 14:03:01ID: 9373517

Erm... redoing the if statement to support blanks too...

if (IsDbNull(dropList.Items.Item(iInteger)) or (dropList.Items.Item(iInteger) = "")) then dropList.Items.Item(iInteger) = "NewValue"

 

by: mondayblueboyPosted on 2003-09-16 at 14:03:54ID: 9373524


sorry, typo error should be Equals() instead of Equal()

 

by: mondayblueboyPosted on 2003-09-16 at 14:05:41ID: 9373545


did alot of mistakes, I post again

If Not IsNothing(droplist.SelectedItem)  Then

  If droplist.SelectedItem.Text.Equals("") Then

      ' assign its value
 
    End If

End If

 

by: BrijBhasinPosted on 2003-09-16 at 14:34:34ID: 9373768

I tried what mondayblueboy posted and I again got this error
System.NullReferenceException: Object reference not set to an instance of an object.

 

by: malharonePosted on 2003-09-16 at 14:51:55ID: 9373900

You've gotta do the following

if not (droplist.selecteditem is nothing orlese droplist.selecteditem.text is nothing orlese droplist.selecteditem.text.trim.length<1) then  '<--- this makes sure that your item is not null andalso text of that item is not null
   messagebox.show droplist.selecteditem.text
else
   if not droplist.selecteditem is nothing then
     droplist.selecteditem.text="YAHOO"
   else
     '''no entry was select
   endif
end if

 

by: BrijBhasinPosted on 2003-09-16 at 14:59:02ID: 9373957

I tried the above , it says expression expected

 

by: malharonePosted on 2003-09-16 at 15:03:55ID: 9373977

where at?

i just ran the below code (with fixing the type for ORELSE) w/o any error

        If Not (droplist.selecteditem Is Nothing OrElse droplist.selecteditem.text Is Nothing OrElse droplist.selecteditem.text.trim.length < 1) Then '<--- this makes sure that your item is not null andalso text of that item is not null
            MessageBox.Show(droplist.selecteditem.text)
        Else
            If Not droplist.selecteditem Is Nothing Then
                droplist.selecteditem.text = "YAHOO"
            Else
                '''no entry was select
            End If
        End If

 

by: mondayblueboyPosted on 2003-09-17 at 05:49:47ID: 9377700


I think the DropDownList does not have any item. Then you should check like the following:

If droplist.Items.Count > 0 Then ' has member item
      If Not IsNothing(droplist.SelectedItem)  Then      ' has item selected
            If droplist.SelectedItem.Text.Equals("") Then      ' does not have value
                  ' do something..
            End If
      End If
End If

The expression IsDBNull(dropList.SelectedItem.text) is absolutely wrong
Because text data type cannot have DBNull value.

 

by: BrijBhasinPosted on 2003-09-17 at 07:04:13ID: 9378308

If the dropdownlist doesnt have any items in there .. is there a way to insert an item?

 

by: GoodJunPosted on 2003-09-17 at 07:19:14ID: 9378430

yes.
droplist.items.add("test")

20120131-EE-VQP-002

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