Question

Public Sub auto_Suggest(ByVal member As String, ByVal table As String, ByVal txt As Object)
    Try
        dta = New DataTable
        'open the connection
        conn.Open()
        'holds the data in the database
        With cmda
            .Connection = conn
            .CommandText = "select " & member & " from " & table
        End With
        '''''''''''''''fill data in the table
        daa.SelectCommand = cmda
        daa.Fill(dta)

        ''function of autocomplete
        Dim r As DataRow
        txt.AutoCompleteCustomSource.Clear()


        For Each r In dta.Rows
            txt.AutoCompleteCustomSource.Add(r.Item(0).ToString)

        Next
        ''''''''''''''''''''''''
    Catch ex As Exception
        MsgBox(ex.Message)
    End Try
    ''''close the connection
    conn.Close()
    daa.Dispose()

End Sub




Private Sub Stock_Load(sender As Object, e As EventArgs) Handles MyBase.Load
    Try
        'call a public sub
        'the job_id is the field of a table , the employees is the name of a table and a textbox is an object
        auto_Suggest("ItemName", "stock", TxtItemName)

        Catch ex As Exception
        MessageBox.Show(ex.Message)

    End Try
End Sub

Answer 1

首先，采用“使用它并失去它”的方法并利用使用块来自动处理连接，命令和读取器是很好的。请参阅下面的示例。

其次，请在Try语句后的第一行设置断点，然后在调试器中逐步执行源代码。如果达到异常，请检查ex变量，并可能检查ex.InnerException（如果有）。

最后，此处的示例使用SQLConnection和SQLCommand（SQL Server）。只需换掉你用于MySQL的任何库，你应该好好去。

Public Sub auto_Suggest(connectionString As String, member As String, table As String, txt As TextBox)
    Try
        txt.AutoCompleteCustomSource.Clear()

        Using cn = New SqlConnection(connectionString)
            cn.Open()

            Using cmd = New SqlCommand("SELECT " & member & " FROM " & table, cn)
                Using dr = cmd.ExecuteReader()
                    While dr.Read
                        txt.AutoCompleteCustomSource.Add(dr(member).ToString)
                    End While
                End Using
            End Using
        End Using
    Catch ex As Exception
        MsgBox(ex.Message)
    End Try
End Sub

我收到auto _Suggest的错误，错误是＆＃34;对象引用没有设置对象的实例＆＃34;

1 个答案: