Hi,

I would like to check if a text field is empty; I'm using this code ...

Dim strTitle As String = String.Empty

Try
   strTitle = Trim(txtTitle.Text)
Catch ex As Exception When strTitle = String.Empty
  MessageBox.Show("error")
End Try


unfortunately, the exception doesn't work...

Anyone any idea's ?

Thanx

john

try =""

'Trim' does not throw an exception.

\\\
If Len(Trim(Me.TextBoxTitle.Text)) = 0 Then
    ...
End If
///

Show quote Hide quote Actuall, String.Trim can throw an exception. Consider the following:
  Dim foo As String
  Console.WriteLine(foo.Trim)

In this case foo is not instanced and thus we try to Trim Nothing. Since
string is an object not a value type, it is not initiated by default and
thus can be null/nothing. Because of this, I always check for nothing on
my strings passed into to methods as parameters before processing them. (if
value = nothing then value = string.Empty). This is particularly noticable
when binding a Combobox's SelectedValue to string property of an object.

You are correct that the TextBox.Text can not pass back nothing, thus in
the OP's code, it will not throw an exception. Furthermore, relying on exceptions
when you can pre-test for a condition is akin to peeing your pants to see
if the fly is unzipped. Thus, checking to see if txtTitle.Text.Trim=String.Empty
is much better than using exceptions and try..catch blocks anyway.

Jim Wooley
http://devauthority.com/blogs/jwooley/default.aspx

Show quote Hide quote That's true, but I am using 'Microsoft.VisualBasic.Strings.Trim' instead of
'String.Trim'.  Instead of performing the check if the variable containing
the string to be trimmed is 'Nothing' I delegate this check to 'Trim'.

John Devlon wrote:
That's because reading and trimming an empty string from a textbox doesn't
throw an exception.

Try this:

\\\
    Dim strTitle As String = String.Empty

    strTitle = Trim(txtTitle.Text)
    If Len(strTitle) = 0 Then
        MessageBox.Show("error")
    End If
///

Show quote Hide quote If Trim(txtTitle.Text) = "" Then MsgBox ("error")

Cheers.

I would use:

If not txtTitle.Text is nothing andalso txtTitle.Text.Trim.Length<=0 then
   'do something if true
end if
Show quoteHide quote

Dennis,

Can you show me a scenario where the .Text property of a TextBox can contain Nothing.  I can't find one.

I have put the following in a button click event:

If TextBox1.Text Is Nothing Then

   MsgBox("Textbox1.Text is Nothing")

Else

   TextBox1.Text = Nothing

End If



I can click on the TextBox as many times as I want and I never get the message box.



BTW, I'm using VB.Net 2005.

You are correct but whenever I check for a string's length, etc., I always
check for nothing first...I think it's good practice to get in this habit and
avoid unexpected errors since a lot of softwre doesn't check for boundaries
like variables set to nothing.
Show quoteHide quote

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