.executenonquery() 错误 没有为一个或多个必需参数提供值

Question

Imports System.Data.OleDb
Public Class LoginForm
    Dim connstring As String = "Provider=Microsoft.ACE.OLEDB.12.0;Data Source=C:UsersUserDesktopthesisYBIM.accdb"
    Dim conn As New OleDbConnection
    ' TODO: Insert code to perform custom authentication using the provided username and password 
    ' (See http://go.microsoft.com/fwlink/?LinkId=35339).  
    ' The custom principal can then be attached to the current thread's principal as follows: 
    '     My.User.CurrentPrincipal = CustomPrincipal
    ' where CustomPrincipal is the IPrincipal implementation used to perform authentication. 
    ' Subsequently, My.User will return identity information encapsulated in the CustomPrincipal object
    ' such as the username, display name, etc.

    Private Sub LoginForm_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        conn.ConnectionString = connstring
        If conn.State = ConnectionState.Closed Then
            conn.Open()
            MsgBox("welcome")
        Else
            MsgBox("Cannot connect to database")
        End If
    End Sub
    Private Sub OK_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles OK.Click
        Dim SqlQuery As String = ("SELECT * FROM tablelogin WHERE Username= @field1 AND Password=@field2")
        Dim SqlCommand As New OleDbCommand
        Dim Sqlrdr As OleDbDataReader
        With SqlCommand
            .CommandText = SqlQuery
            .Connection = conn
            .Parameters.AddWithValue("@field1", UsernameTextBox.Text)
            .Parameters.AddWithValue("@field2", PasswordTextBox.Text)
            .ExecuteNonQuery()
        End With
        Sqlrdr = SqlCommand.ExecuteReader()
        If (Sqlrdr.Read() = True) Then
            home.ShowDialog()
            Me.Hide()
        Else
            MsgBox("wong input")
        End If

    End Sub
End Class

Answer 1

代码中有两件事需要注意，您可以进行补救。

1* 参数命名不正确。这：

    .Parameters.AddWithValue("@field1", UsernameTextBox.Text)
    .Parameters.AddWithValue("@field2", PasswordTextBox.Text)

应该是这样的：

.Parameters.AddWithValue("field1", UsernameTextBox.Text)
.Parameters.AddWithValue("field2", PasswordTextBox.Text)

2* 您正在执行该命令两次。从 With 语句中删除.ExecuteNonQuery()，并更改：

Sqlrdr = SqlCommand.ExecuteReader()

自

Dim ret As Integer
ret = SqlCommand.ExecuteNonQuery()

而不是使用 Sqlrdr.Read() ，只需检查 ret 是否> 0（执行非查询返回受命令影响的行数）。