各位幫我看看那里有錯

Dim strcmd As String
        Dim sqlcon As SqlConnection = New SqlConnection(strcon)
        sqlcon.Open()
        strcmd = "select id from t_login"
        Dim sqlcmd As SqlCommand = New SqlCommand(strcmd, sqlcon)
        Dim dr As SqlDataReader
        dr = sqlcmd.ExecuteReader
        Do While dr.Read()
            If Trim(ComboBox1.Text) = dr.Item(0) Then     '這里我的數據庫里有相對應的資料但是不行運以下代碼
                MsgBox("a")
                Exit Sub
            ElseIf Trim(ComboBox1.Text) <> dr.Item(0) Then’反而運行這里，也就是未找到
                MsgBox("用戶ID錯誤或不存在請查檢！")
            End If
        Loop