vb.net - 如何在vb.net中使用try catch和finally block？

Question

下面是我想使用try catch和finally block 的代码，但我无法这样做，我是编程新手，请帮我在vb中的下面的代码中引入try catch和finally block 。 net，还有助于编写finally block 的代码，我将在其中检查连接是否打开，我的连接已打开，那么它应该在finally block 中关闭，但在检查后。如果

条件..

else
    'Try
        con.Open()
        adp = New OleDbDataAdapter("select * from Login ", con)

        adp.Fill(dt, "Login")
        Dim i As Integer
        For i = 0 To dt.Tables(0).Rows.Count - 1
            If (cbType.Text = dt.Tables(0).Rows(i).Item(1) And txtUname.Text = dt.Tables(0).Rows(i).Item(2) And txtPass.Text = dt.Tables(0).Rows(i).Item(3)) Then

                MDIParent1.Show()


                Exit Sub


            End If
            '                Catch ex As Exception


        Next

        MsgBox("You Are Not A Valid User!!", MsgBoxStyle.Information)
    End If

Answer 1

非常简单。

请参阅下面的代码。

Try

    'In this block your program will try to execute your code.
    'If it catches any runtime error it will go to the Catch Block straight away without executing the next code in your Try Block.
    'If there are no errors then Finally Block will be executed after Try Block. Catch Block will be skipped.

Catch

    'It will display the errors here.
    'So you can use Catch ex as exception.
    'If you want to see the errors in Messagebox you can write the below line.
    'MessageBox.Show(ex.Message)

Finally

    'If your program finds errors or not this block will be executed always.

End Try

因此您可以在代码中使用 Try...Catch，如下所示:

Dim ValidUser as Boolean = False

Try
        con.Open()
        adp = New OleDbDataAdapter("select * from Login ", con)

        adp.Fill(dt, "Login")
        Dim i As Integer

        For i = 0 To dt.Tables(0).Rows.Count - 1
            If (cbType.Text = dt.Tables(0).Rows(i).Item(1) And txtUname.Text = dt.Tables(0).Rows(i).Item(2) And txtPass.Text = dt.Tables(0).Rows(i).Item(3)) Then

                ValidUser = true


                Exit For


            End If

        Next

        If ValidUser = True
             MDIParent1.Show()
        Else
             MsgBox("You Are Not A Valid User!!", MsgBoxStyle.Information)
        End If

Catch ex As Exception

    MessageBox.Show(ex.Message)

Finally

    if con.State = ConnectionState.Open then
        con.close()
    End If

    ValidUser = False

End Try