根据另一个组合框值将数据填充到组合框

Question

我正在使用 VB 将 Access 数据库连接到我的程序，并且我有两个组合，我希望第二个组合数据源取决于第一个组合选定项，这是我到目前为止所做的代码：

 Try
     Dim dbcon As New OleDb.OleDbConnection("Provider=Microsoft.ACE.OLEDB.12.0;Data Source=|DataDirectory|\inventorysys.accdb;Persist Security Info=False;")
        dbcon.Open()
        Dim sqlquery As String = ("SELECT DISTINCT Brand FROM inventory WHERE Category = ' " & catogerycombotxt.SelectedItem & " ' ")
        Dim comm As New OleDb.OleDbCommand(sqlquery, dbcon)
        Dim rs As OleDb.OleDbDataReader = comm.ExecuteReader
        Dim dt As DataTable = New DataTable
        dt.Load(rs)
        ' as an example set the ValueMember and DisplayMember'
        ' to two columns of the returned table'
        brandcombotxt.DataSource = dt
        brandcombotxt.ValueMember = "Brand"
        brandcombotxt.DisplayMember = "Brand"

        dbcon.Close()
    Catch ex As Exception
        MsgBox(ex.Message)
    End Try

它没有错误但没有结果，希望你能帮助我

Answer 1

两件事：

首先，我认为您的问题是在您的查询中，您将所选值连接在两个空格之间：

Dim sqlquery As String = ("SELECT DISTINCT Brand FROM inventory WHERE Category = ' " & catogerycombotxt.SelectedItem & " ' ")

应该是

Dim sqlquery As String = ("SELECT DISTINCT Brand FROM inventory WHERE Category = '" & catogerycombotxt.SelectedItem & "'")

第二：了解parameterized queries。出于很多原因，这是一种比字符串连接更好的创建和执行 sql 查询的方法。