如何在VB.NET中实现厨房订单表单的自动更新显示

问题描述 #

我正在开发一套包含厨房显示系统的项目，已编写GetOrders()方法从数据库查询状态为'Pending'的订单，并通过WinForms控件生成可视化面板展示订单信息，但无法实现表单内容的自动更新。尝试使用Do循环时，未登录系统就出现报错；调用GetOrders().Refresh也无效果，希望得到解决该问题的方法。

现有代码 #

Public Sub GetOrders()

    Try

        kitchenFlowLayoutPanel.Controls.Clear()

        Dim i As Integer
        Dim sql As String

        sql = "SELECT c.cart_id, c.invoice_no, c.table_no, c.sale_time, f.item_name, c.serve_size, c.quantity FROM tbl_cart AS c INNER JOIN tbl_food AS f on f.item_id = c.items_id WHERE c.status='Pending'"

        conn.Open()
        cmd = New MySqlCommand(sql, conn)
        cmd.ExecuteReader()
        conn.Close()

        Dim dTable1 As New DataTable()
        Dim dAdaptor1 As New MySqlDataAdapter(cmd)
        dAdaptor1.Fill(dTable1)

        Dim panel1 As FlowLayoutPanel
        Dim panel2 As FlowLayoutPanel

        For i = 0 To dTable1.Rows.Count - 1

            panel1 = New FlowLayoutPanel
            panel1.AutoSize = True
            panel1.Width = 260
            panel1.Height = 500
            panel1.FlowDirection = FlowDirection.TopDown
            panel1.BorderStyle = BorderStyle.FixedSingle
            panel1.Margin = New Padding(10, 10, 10, 10)

            panel2 = New FlowLayoutPanel
            panel2.BackColor = Color.FromArgb(50, 55, 89)
            panel2.AutoSize = True
            panel2.Width = 230
            panel2.Height = 125
            panel2.FlowDirection = FlowDirection.TopDown
            panel2.Margin = New Padding(0, 0, 0, 0)

            Dim label1 As New Label
            label1.ForeColor = Color.White
            label1.Margin = New Padding(10, 5, 3, 0)
            label1.Font = New Font(label1.Font, FontStyle.Bold)
            label1.AutoSize = True

            Dim label2 As New Label
            label2.ForeColor = Color.White
            label2.Margin = New Padding(10, 5, 3, 0)
            label2.AutoSize = True

            Dim label3 As New Label
            label3.ForeColor = Color.White
            label3.Margin = New Padding(10, 5, 3, 0)
            label3.AutoSize = True

            Dim label4 As New Label
            label4.ForeColor = Color.White
            label4.Margin = New Padding(10, 5, 3, 0)
            label4.AutoSize = True

            Dim label5 As New Label
            label5.ForeColor = Color.White
            label5.Margin = New Padding(10, 5, 3, 0)
            label5.AutoSize = True

            label1.Text = "Entry ID   : " & dTable1.Rows(i)("cart_id").ToString
            label2.Text = "Invoice No : " & dTable1.Rows(i)("invoice_no").ToString
            label3.Text = "Table No   : " & dTable1.Rows(i)("table_no").ToString
            label4.Text = "Order Time : " & dTable1.Rows(i)("sale_time").ToString
            label5.Text = Environment.NewLine & "ORDERED ITEM : " & Environment.NewLine & Environment.NewLine & " Item : " & dTable1.Rows(i)("item_name").ToString & Environment.NewLine & " Serve Size : " & dTable1.Rows(i)("serve_size").ToString & Environment.NewLine & " Qty: " & dTable1.Rows(i)("quantity").ToString & Environment.NewLine & Environment.NewLine

            panel2.Controls.Add(label1)
            panel2.Controls.Add(label2)
            panel2.Controls.Add(label3)
            panel2.Controls.Add(label4)
            panel2.Controls.Add(label5)

            panel1.Controls.Add(panel2)

            Dim btn As New Guna.UI2.WinForms.Guna2Button

            btn.AutoRoundedCorners = True
            btn.Size = New Size(100, 35)
            btn.FillColor = Color.FromArgb(241, 85, 126)
            btn.Margin = New Padding(60, 5, 3, 10)
            btn.Location = New Point(0, 0)
            btn.Text = "Complete"
            btn.Tag = dTable1.Rows(i)("cart_id").ToString ' store id 

            AddHandler btn.Click, AddressOf btn_Click

            panel2.Controls.Add(btn)

            kitchenFlowLayoutPanel.Controls.Add(panel1)

        Next

    Catch ex As Exception

        conn.Close()
        MsgBox(ex.Message, vbCritical)

    End Try

End Sub

解决方法 #

1. 修复数据库查询逻辑错误 #

现有代码中cmd.ExecuteReader()属于冗余操作，会占用数据库连接导致后续DataAdapter.Fill无法正常执行，直接删除该段代码，改用Using语句自动释放资源：

' 移除原有的conn.Open()、cmd.ExecuteReader()、conn.Close()三行

' 替换为以下代码
Dim dTable1 As New DataTable()
Using cmd As New MySqlCommand(sql, conn)
    Using dAdaptor1 As New MySqlDataAdapter(cmd)
        dAdaptor1.Fill(dTable1)
    End Using
End Using

2. 用Timer实现定时自动刷新 #

WinForms中不要用Do循环阻塞UI线程，改用System.Windows.Forms.Timer控件实现定时更新：

• 在窗体设计器添加Timer控件（命名为orderRefreshTimer）
• 设置Interval属性（例如5000，代表每5秒刷新一次）
• 在窗体加载事件中启用Timer，并绑定Tick事件：

Private Sub Form_Load(sender As Object, e As EventArgs) Handles MyBase.Load
    orderRefreshTimer.Interval = 5000
    ' 注意：请在登录成功后再启用Timer，避免未登录时触发数据库连接错误
    ' orderRefreshTimer.Enabled = True
End Sub

Private Sub orderRefreshTimer_Tick(sender As Object, e As EventArgs) Handles orderRefreshTimer.Tick
    GetOrders()
End Sub

3. 确保UI操作在主线程执行 #

如果后续采用异步查询数据库，必须通过Invoke确保控件更新在UI线程进行：

If kitchenFlowLayoutPanel.InvokeRequired Then
    kitchenFlowLayoutPanel.Invoke(Sub() GetOrders())
Else
    GetOrders()
End If

4. 解决未登录报错问题 #

将Timer的启用逻辑放在登录成功之后，确保数据库连接conn已正确初始化，避免未登录时触发数据库连接错误。

内容的提问来源于stack exchange，提问作者Blood Rue