无法投射类型的对象...

Question

我想知道下面的代码有什么问题。我正在创建一个用户可以更改密码的表单，但每当我尝试运行系统时总是会出错。任何帮助将不胜感激！谢谢。

Public Class Form7

Dim cnString = "Provider=Microsoft.ACE.OLEDB.12.0;" & _
             "Data Source=C:\Thesis\Thesis\Database1.accdb"
Private Sub TextBox1_TextChanged(sender As System.Object, e As System.EventArgs) Handles TextBox2.TextChanged

End Sub

Private Sub Button1_Click(sender As System.Object, e As System.EventArgs) Handles Button1.Click
    Try
        Using dbCommand As New System.Data.OleDb.OleDbCommand("select count ([Password]) from students where [Password] like ?", cnString)
            dbCommand.Parameters.AddWithValue("@password", textbox1.Text)
            Dim result As Integer = DirectCast(dbCommand.ExecuteScalar(), Integer)
            If result = 1 Then
                Dim sqlquery As String = "UPDATE students SET StudFacID = @STUDID, [Password] = @Password" & _
                             "WHERE ID = StudFacID"

                ' Use this form to initialize both connection and command to 
                ' avoid forgetting to set the appropriate properties....

                Using conn = New System.Data.OleDb.OleDbConnection(cnString)
                    Using cmd = New System.Data.OleDb.OleDbCommand(sqlquery, cnString)

                        cnString.Open()
                        cmd.Parameters.AddWithValue("@STUDID", TxtID.Text)
                        cmd.Parameters.AddWithValue("@Password", TextBox2.Text)
                    End Using

                End Using
            End If

                End Using 

    Catch ex As Exception
        MsgBox(ex.ToString)
    End Try
End Sub

结束班

Answer 1

您正在尝试构建OldDbCommand对象：

New System.Data.OleDb.OleDbCommand("your sql command", cnString)

使用the constructor that takes two arguments。该构造函数需要String和OleDbConnection，但您需要为String和String提供String和OldDbConnection。如错误所示，Using dbConnection As New OleDbConnection(cnString) Using dbCommand As New OleDbCommand("your sql command", dbConnection) ' the rest of your code End Using End Using 无法转换为conn，因此此尝试失败。

创建an OleDbConnection object以与命令对象一起使用。也许是这样的：

cmd

（基本上，您应该使用{{1}}和{{1}}对象执行完全相同的操作。）

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此外，作为附注，这是非常重要 ...您应 不 将用户密码存储为 纯文字 。用户密码应该进行哈希处理，并且永远不会可以恢复。您目前正在做的事情是对您的用户非常不负责任。