how to write an event that will fire when the focus on control changes in vb.net

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.NET3.5

Hi Team, i am trying to write an event in vb.net which will fire when the focus of control changes from one to another. I have form with 7 attributes for 15 users ( which includes text box and combo box as well), using this form i am entering user details to the DB. Now for the validation purpose i need to write an event that checks if the same data already exists in the DB, and it will show a label next to the control, hence i need to write event that will fire as soon as the focus from the control shifts to the other control. I am new to vb.net.Please help.
Thanks in advance

Posted 2-Aug-10 5:16am

souvikd

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E.F. Nijboer · Answer 1 · 2010-08-02T05:26:00

Solution 1

You simply add the Enter/Leave event handler of all the controls to the specific handler.

VB

for each AControl in Me.Controls 
        If TypeOf AControl Is TextBox Or _
           TypeOf AControl Is ComboBox Or _
           TypeOf AControl Is DateTimePicker Or _
           TypeOf AControl Is NumericUpDown Or _
           TypeOf AControl Is MaskedTextBox Then
            AddHandler AControl.Enter, AddressOf Control_Enter
            AddHandler AControl.Leave, AddressOf Control_Leave
        End If
Next

Good luck!

Posted 2-Aug-10 5:26am

E.F. Nijboer

Updated 2-Aug-10 5:29am

v2

Comments

souvikd 2-Aug-10 11:30am

i didnt understand to which handler i should add this code, please explain

E.F. Nijboer 2-Aug-10 12:24pm

The most easy way is to simply put a TextBox on a form and create an Enter and Leave handler using the editor. You will get two handlers called TextBox1_Enter and TextBox1_Leave. Use these two handlers instead of the Control_Enter and Control_Leave.

William Winner · Answer 2 · 2010-08-02T07:26:00

You can do the Enter and Leave as was suggested in the other box, or you can just use the LostFocus event.

If I were writing something similar to what you were describing, I would expect it to look something like this:

VB

Private Sub Controls_LostFocus(ByVal sender As Object, ByVal e As System.EventArgs) _
      Handles TextBox1.LostFocus, TextBox2.LostFocus, ComboBox1.LostFocus
  Using dbConn As New OleDb.OleDbConnection("some connection string")
    Dim cmd As New OleDb.OleDbCommand("SELECT * FROM Table WHERE User=? ")
    cmd.Parameters.Add(userName)

    Select Case CType(sender, Control).Name
        Case TextBox1.Name
            cmd.CommandText = cmd.CommandText & "TextBox1Attribute=?"
            cmd.Parameters.Add(TextBox1.Text)
        Case TextBox2.Name
            cmd.CommandText = cmd.CommandText & "TextBox2Attribute=?"
            cmd.Parameters.Add(TextBox2.Text)
        Case ComboBox1.Name
            cmd.CommandText = cmd.CommandText & "ComboBox1Attribute=?"
            cmd.Parameters.Add(ComboBox1.Text)
    End Select

    If Not IsDBNull(cmd.ExecuteScalar) Then
        'add the image indicating that this value already exists.
    End If    
  End Using
End Sub

[E.F. noted a problem. I actually started with:

VB

If TypeOf sender Is TextBox Then
  CType(sender, TextBox)...
End If

and changed it because I needed to include ComboBoxes as well and didn't change the CType line.