vb.net 组合框与另一个组合框相连

Question

so i need help in this following code:

 Private Sub cbxkelas_SelectedIndexChanged(sender As Object, e As EventArgs) Handles cbxkelas.SelectedIndexChanged
    Try
        Dim kel As String
        kel = cbxkelas.SelectedText.FirstOrDefault()
        If kel = "2" Or "4" Or "6" Then
            cbxsemes.SelectedItem = "Genap"
        Else
            cbxsemes.SelectedItem = "Ganjil"
        End If
        cbxsemes.Items.Clear()
    Catch ex As Exception
        MsgBox(ex.Message)
    End Try

End Sub

im trying to get a cbxsemex(combobox) value depending on the choice made at cbxkelas(combobox) first character but when i choose "1psi2" at cbxkelas it still show "Genap" in cbxsemes.

Answer 1

You have Option Strict set to OFF.
This settings allows a syntax like the one in this line

 If kel = "2" Or "4" Or "6" Then

to pass through but in your context it makes no sense because the line is evaluated as

 If (kel = "2") Or ("4" Or "6") Then

and, with Option Strict set to OFF, an automatic conversion from the strings "4" and "6" to booleans happens. Of course this conversion gives back true as result (if the string was "0" you will get false)

You code should be

 If kel = "2" Or kel = "4" Or kel = "6" Then

So, my recommendation is to change Option Strict to ON. Probably, after this, your program will fail to compile correctly but it will also highlight a lot of other places where you should look carefully if you are really getting the result expected.

Still it is not clear why you remove all items from the same combobox that you have just set the selected item.

Answer 2

您的情况必须更改为

If kel = "2" Or kel = "4" Or kel = "6" Then