Question

我的连接字符串可能会出现什么问题。它报告cnn未声明。

        Dim cnn As New OleDbConnection
        If rdbtnNewDbase.Checked = True Then
             Dim cnn As new OleDbConnection("Provider=Microsoft.Jet.OLEDB.4.0; Persist Security Info=false; Data Source=..\HCHPClosedIn11.mdb")
        ElseIf rdbtnOldDbase.Checked = True Then
            Dim cnn As New OleDbConnection("Provider=Microsoft.Jet.OLEDB.4.0; Persist Security Info=false; Data Source=..\HCHPold.mdb")
        End If

Answer 1

您尝试在If/End If范围内重新声明您的连接对象。实际上，您的代码甚至无法编译。此外，变量不能在声明范围之外使用。

你真正想做的是：

Dim cnn As OleDbConnection
If rdbtnNewDbase.Checked = True Then
    cnn = New OleDbConnection("Provider=Microsoft.Jet.OLEDB.4.0; Persist Security Info=false; Data Source=..\HCHPClosedIn11.mdb")
ElseIf rdbtnOldDbase.Checked = True Then
    cnn = New OleDbConnection("Provider=Microsoft.Jet.OLEDB.4.0; Persist Security Info=false; Data Source=..\HCHPold.mdb")
End If

或者，让它更短更清晰：

Dim cs As String = 
    "Provider=Microsoft.Jet.OLEDB.4.0; Persist Security Info=false; Data Source=..\" &
    If(rdbtnNewDbase.Checked, "HCHPClosedIn11.mdb", "HCHPold.mdb")

Dim cnn As New OleDbConnection(cs)

Answer 2

试试这个：

Using cnn As New OleDbConnection(string.Format(
    "Provider=Microsoft.Jet.OLEDB.4.0; Persist Security Info=false; Data Source=..\{0}", 
     If(rdbtnNewDbase.Checked, "HCHPClosedIn11.mdb", "HCHPHold.mdb" ))

    '...
End Using

在if语句中使用连接字符串

2 个答案: