Question

VB.NET访问ACCESS数据库，查询时，提示dr = cmd.ExecuteReader()至少一个参数没被指定值

Imports System.Data.OleDb
Public Class Form1
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
Dim con As New OleDbConnection
con.ConnectionString = "Provider=Microsoft.ACE.OLEDB.12.0;Data Source=test.mdb"
Dim table As New DataTable()
Dim myda As New OleDbDataAdapter("select * from test", con)
Dim ds As New DataSet()
Dim cmd As New OleDbCommand
'定义一个OLEDBReader方法来读取数据库
Dim dr As OleDbDataReader
con.Open()
cmd.Connection = con
myda.Fill(ds, "test")
myda.Fill(table)
ComboBox1.DataSource = ds
Me.DataGridView1.DataSource = table
Me.ComboBox1.DisplayMember = "test.设备"
cmd.CommandText = "select ip from test where 设备=" & ComboBox1.Text & ""
dr = cmd.ExecuteReader()
If dr.Read() Then
TextBox1.Text = dr(0)
End If
'完成后关闭dr.con等释放资源
dr.Close()
con.Close()
End Sub
End Class

-----------------------执行时，总提示dr = cmd.ExecuteReader()至少一个参数没被指定值，请问各位大侠，这个是怎么回事呢？该怎么解决？

Answer 1

看起来,应该是"select ip from test where 设备=" & ComboBox1.Text & ""这里出错了
你试试:
"select ip from test where 设备='" & ComboBox1.Text & "'"
这样应该不会提示这个错误了,但TextBox1当中可能不会显示任何内容
因为你的ComboBox1.Text 的内容应该是空的