Question

我有一个从USB徽章阅读器获取用户ID的功能，用于登录应用程序。当我运行应用程序时，直到我滑动标记才会出现登录窗口。我需要知道是否可以加载窗口，然后开始运行从USB获取数据的功能。

谢谢：）

Private Sub SerialPort1_DataReceived()
    'Threading.Thread.SpinWait(1000)
    OpenPort()
    If SerialPort1.IsOpen() Then

        byteEnd = SerialPort1.NewLine.ToCharArray
        'read entire string until .Newline 
        readBuffer = SerialPort1.ReadLine()
        readBuffer = readBuffer.Remove(0, 1)
        readBuffer = readBuffer.Remove(8, 1)
        WWIDTextBox.AppendText(readBuffer)

    End If
End Sub

Private Sub Form1_Activated(ByVal sender As Object, _
ByVal e As System.EventArgs) Handles MyBase.Activated
    SerialPort1_DataReceived()
End Sub

Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
    'SerialPort1_DataReceived()
End Sub

Answer 1

问题是您正在调用ReadLine方法，这是一种阻塞（同步）方法。换句话说，当您调用它时，该方法不会返回该值，直到它具有要返回的值。因此，它会在当前线程上停止执行，直到读取完整的行（刷卡时）。由于您在调用它时处于UI线程，因此它会锁定UI，直到刷过徽章。

您可以从其他线程执行工作，而不是从UI线程调用SerialPort1_DataReceived方法。最简单的方法是将BackgroundWorker组件拖到设计器中的表单上。然后你可以添加这样的代码：

Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
    BackgroundWorker1.RunWorkerAsync()
End Sub

Private Sub BackgroundWorker1_DoWork(sender As Object, e As DoWorkEventArgs) Handles BackgroundWorker1.DoWork
    OpenPort()
    If SerialPort1.IsOpen() Then
        byteEnd = SerialPort1.NewLine.ToCharArray
        Dim readBuffer As String = SerialPort1.ReadLine()
        readBuffer = readBuffer.Remove(0, 1)
        readBuffer = readBuffer.Remove(8, 1)
        e.Result = readBuffer
    End If
End Sub

Private Sub BackgroundWorker1_RunWorkerCompleted(sender As Object, e As RunWorkerCompletedEventArgs) Handles BackgroundWorker1.RunWorkerCompleted
    WWIDTextBox.AppendText(CStr(e.Result))
End Sub

Answer 2

在VS2013上工作时，我遇到了同样的问题，我需要进行datagridview刷新（gridrows中的颜色）。这对我有用。

Sub MyForm_VisibleChanged(sender As Object, e As EventArgs) Handles Me.VisibleChanged

            If Me.Visible Then
                'do action...
            End If

End Sub

Answer 3

尝试Form Activated活动

Private Sub Form1_Activated(ByVal sender As Object, _
    ByVal e As System.EventArgs) Handles MyBase.Activated
 'Call your function here
End Sub

调用函数After the Form Loads ...

Answer 4

Private Sub loadCombo()
    Dim sqlconn As New OleDb.OleDbConnection
    Dim connString As String
    connString = ""
    Dim access As String
    access = "select slno from atable"
    Dim DataTab As New DataTable
    Dim DataAdap As New OleDbDataAdapter(access, connString)
    DataAdap.Fill(DataTab)
    ComboBox1.DataSource = DataTab
    ComboBox1.DisplayMember = "slno"

End Sub

如何在VB中加载表单窗口后运行函数/子？

4 个答案: