在if语句中使用连接字符串

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,使其更短更清晰:

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)