Question

警告BC42104：变量＆＃39;通过＆＃39;在被赋值之前使用。在运行时可能会产生空引用异常。

这是我的代码：

Private Sub btnLogin_Click(sender As Object, e As EventArgs) Handles btnLogin.Click
    Dim uname As String = ""
    Dim pword As String
    Dim username As String = ""
    Dim pass As String
    If TextBox1.Text = "" Or TextBox2.Text = "" Then
        MsgBox("Please fill the info")
    Else
        uname = TextBox1.Text
        pword = TextBox2.Text
        Dim query As String = "Select Password From Register where Username= '" & uname & "';"
        Dim dbsource As String = "Provider=Microsoft.ACE.OLEDB.12.0;Data Source=C:\Users\Gui\Documents\Database4.accdb"
        Dim conn = New OleDbConnection(dbsource)
        Dim cmd As New OleDbCommand(query, conn)
        conn.Open()
        Try
            pass = cmd.ExecuteScalar().ToString
        Catch ex As Exception
            MsgBox("Username does not exit")
        End Try
        If (pword = pass) Then
            MsgBox("Login success")
            Reg.Show()
            If Reg.Visible Then
                Me.Hide()
            End If

        Else
            MsgBox("login Failed")
            TextBox1.Clear()
            TextBox2.Clear()
        End If
    End If
End Sub

Answer 1

正如错误所说，您没有初始化变量传递，在某些情况下，您最终可能会使用它。

确切地说，如果控件落在＆＃39; catch ＆＃39;阻止，变量＆＃39; 传递＆＃39;将没有任何值，这意味着如果没有此变量具有任何值，则可能会达到If (pword = pass)语句。

要修复错误，只需在初始化时为变量分配空值或空字符串。例如，使用以下语句：

Dim pass As String = "";

BC42104错误代码如何修复此错误？

1 个答案: