声明预期

Question

美好的一天。请告诉我 将光标放在cmd变量上时，为什么会出现“预期声明”错误消息。我该怎么办？！ ..代码如下：

Imports System.Data.Sqlclient
Imports System.Configuration

Partial Class _Default
    Inherits Page
    Private Shared Connectionstr As String ="DataSource=localhost;initialCatalog=Orders;Integrated Security=true"
    Dim conn As SqlConnection = New SqlConnection(Connectionstr)
    Dim cmd As SqlCommand = conn.CreateCommand()
   cmd.CommandText="SELECT * FROM dbo.Customers"
End Class 

Answer 1

您正在尝试在Property，Function或Method外部使用变量命令。至少，尝试将命令包装在方法（Sub）中，该方法使用数据执行所需的操作：

Partial Class _Default     继承页面

Private Sub DoSomethingWithCustomers()
    Dim conn As SqlConnection = New SqlConnection(Connectionstr)
    Dim cmd As SqlCommand = conn.CreateCommand()
    cmd.CommandText = "SELECT * FROM dbo.Customers"

    conn.Open()
    Dim dr = cmd.ExecuteReader()
    ' Do something with the data returned . . .
    ' ...
    ' Now Cleanup:
    conn.Close()
    cmd.Dispose()
    conn.Dispose()
End Sub

通过将数据访问对象包装在Using块中可以改善上述问题，这些块可以为您正确处理非托管资源：

Private Sub DoSomethingBetterWithCustomers()
    Dim SQL As String = "SELECT * FROM dbo.Customers"
    Using conn As New SqlConnection(Connectionstr)
        Using cmd As New SqlCommand(SQL, conn)
            conn.Open()
            Dim dr = cmd.ExecuteReader()
            ' Do something with the data returned
            ' . . . 
            dr.Close()
        End Using ' Using Block takes carre of Disposing SqlCommand
    End Using ' Using Block takes care of Closing and Disposing Connection
End Sub

除此之外，很难知道你正在尝试用你的代码做什么，所以上面的两个例子真的非常基本和一般。