Home / Questions / 154445
Accepted
Adrian Hernando Solanas
Asked: 2020-04-10 15:44:32 +0800 CST 2020-04-10 15:44:32 +0800 CST

你调用的对象是空的。VB.NET

  • 772

我正在尝试从此类启动命令：

Imports System.Data.OleDb
Imports System.IO

Public Class GestionSql
    Private sReturn As String = ""
    Private sConection As String = "Provider=Microsoft.Jet.OLEDB.4.0; Data Source=" +Directory.GetCurrentDirectory() + "\TPV.mdb;"
    Private oConection As OleDb Connection
    Public oCommand As New OleDbCommand

    Public Function Launch(ByVal value As String) As String
        Try
            oConection.Open()
            oConection = New OleDbConnection(sConection)
            oCommand.CommandText = Value
            sReturn = oCommand.ExecuteNonQuery()
            oConection.Close()
            MessageBox.Show("La contraseña es: " + sReturn.ToString)
        Catch ex As Exception
            MessageBox.Show(ex.ToString)
        End Try
        Return sReturn
    End Function
End Class

在这堂课中：

Public Class IDVendedor
    Private GestionSql As New GestionSql
    Private sCmd As String
    Private sPass As String

    Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
        'Montamos y lanzamos el comando
        sCmd = "SELECT Password FROM Vendedores WHERE Id=" + id.Text
        sPass = GestionSql.Launch(sCmd)
    End Sub
End Class

我得到错误：

你调用的对象是空的。它告诉我错误在 sCmd 参数的 ExecuteNonQuery 中。

vb.net

3 Answers

  1. Best Answer

    错误Referencia a objeto no establecida como instancia de un objeto将在编程世界中陪伴您多年，但很快您就会习惯立即知道错误在哪里:)

    那条消息是什么意思？

    您正在从尚未初始化（“未设置为对象的实例”）的对象变量（“对象引用”）读取属性或执行函数。也就是说，您声明了一个变量并使用了它，而没有先给它赋值。

    错误出现在捕获的第 15 行，因为您已经反转了变量的初始化oConexion（第 16 行）和第一次使用（第 15 行）：

    oConection.open()
oConection = New OleDbConnection(sConection)

    要解决此问题，您只需oConexion在打开连接之前初始化变量：

    oConection = New OleDbConnection(sConection) 
oConection.open()
    • 2

  2. 在代码中，我看到您在初始化之前尝试使用 oConnection，理论上您的问题可以通过更改来解决：

        oConection.Open()
    oConection = New OleDbConnection(sConection)

    为了这：

        oConection = New OleDbConnection(sConection)//primero creas el objeto
    oConection.Open()//despues lo utilizas

    说明：oConection它与被初始化或未被初始化相同null，null您无法访问其方法或属性，因此在调用之前.open()您需要在使用=new创建此对象的新实例时为其分配一个值，这就是您避免Object not错误初始化。

    我看到的是您需要初始化 oConnection，但您必须对其进行验证，检查图像以查看它是否可以以任何方式帮助您。

    在此处输入图像描述

    • 2

  3. 最后我通过以下方式解决了它：

    Imports System.Data.OleDb
Imports System.IO

Public Class GestionSql
Private sReturn As String = ""
Private sConection As String = "Provider=Microsoft.Jet.OLEDB.4.0; Data Source=" + Directory.GetCurrentDirectory() + "\TPV.mdb;"
Private oConection As New OleDbConnection(sConection)
Public oCommand As New OleDbCommand
'Protected daAdapter As New SqlDataAdapter(sCmd, oConection)
'Protected dsDataSet As New DataSet

'Lanzar comandos con respuesta (SELECT)
Public Function Launch(ByVal value As String) As String
    Try
        oConection.Open()
        oCommand.CommandText = value
        oCommand.CommandType = CommandType.Text
        oCommand.Connection = oConection
        sReturn = oCommand.ExecuteScalar()
        oConection.Close()
        MessageBox.Show("La contraseña es: " + sReturn.ToString)
    Catch ex As Exception
        MessageBox.Show(ex.ToString)
    End Try
    Return sReturn
End Function
End Class
    • 0