vb.net - 有没有办法从 vb.net 中的表列、循环和循环中检索记录值

Question

对不起我的英语不好

1. 当用户单击“开始”按钮时，我试图显示控件中Phone列中的所有记录。Textbox1我希望看到所有这些记录都传入Textbox1While 它正在处理For循环。但它目前的处理速度非常快，所以我只能看到Textbox1. 我怎么了？

2. 在处理For循环时，我将“开始”按钮更改为“停止”按钮。因此，当我单击按钮并且它当前的Text值等于 时"Stop"，我希望它跳过For循环并将值传递TextBox1给 my FirstWin。然后它应该将BtnStart.Text背面更改为"Start"

这是我的代码：

Public Class PhoneFortune
    Dim CN As OleDbConnection
    Dim CM As OleDbCommand
    Dim DA As OleDbDataAdapter
    Dim DT As New DataTable

    Private Sub BtnStart_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles BtnStart.Click
        If BtnStart.Text = "Start" Then
            CM = New OleDbCommand("SELECT * FROM TblPhoneNumber", CN)
            DA = New OleDbDataAdapter(CM)
            DA.Fill(DT)
            For i = 0 To DT.Rows.Count - 1
                TextBox1.Text = DT.Rows(i)("Phone")
            Next
            BtnStart.Text = "Stop"
        End If
        If BtnStart.Text = "Stop" Then
            If FirstWin.Text = "" Then
                FirstWin.Text = TextBox1.Text
                BtnStart.Text = "Start"
            ElseIf SecondWin.Text = "" Then
                SecondWin.Text = TextBox1.Text
                BtnStart.Text = "Start"
            ElseIf ThirdWin.Text = "" Then
                ThirdWin.Text = TextBox1.Text
                BtnStart.Text = "Start"
            End If
        End If
    End Sub

    Private Sub PhoneFortune_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        CN = New OleDbConnection("Provider=Microsoft.ACE.OLEDB.12.0;Data Source=database\db.accdb;Jet OLEDB:Database Password=12345;")
        CN.Open()
    End Sub
End Class

Answer 1

我希望我们在同一个页面上，但是如果你想稍微减慢这个过程，你可以在 FOR 循环中使用这两行代码，
System.Threading.Thread.Sleep(1000)
Me.Refresh()其中 1000 是一秒（值以毫秒表示）。

现在那个FirstWin.Text=""等是用来做什么的？您是否尝试开始循环，然后将文本更改为“停止”，以便当用户单击停止时它会在当前记录处停止？转到 youtube 并寻找多线程视频，不知道如何帮助你希望其余的帮助。如果这有用请承认

Answer 2

对于像这样简单的事情，System.Threading.Thread.Sleep(100)（阻止线程）然后Application.DoEvents()（处理任何按钮点击）似乎可以解决问题。

对于更复杂的东西，这种做法会导致重入和难以重现的bug；在那种情况下，你肯定需要异步编程。

Answer 3

    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
            If Button1.Text = "Start" Then
                If TextBox1.Text = "" Then
                    t1 = New Thread(AddressOf Me.PhoneThread)
                    t1.Start()
                    Button1.Text = "Stop"
                Else
                    t1.Resume()
                    Button1.Text = "Stop"
                End If
            Else    'Click Stop
                t1.Suspend()
                Button1.Text = "Start"
                If FirstWin.Text = "" Then
                    FirstWin.Text = TextBox1.Text
                ElseIf SecondWin.Text = "" Then
                    SecondWin.Text = TextBox1.Text
                ElseIf ThirdWin.Text = "" Then
                    ThirdWin.Text = TextBox1.Text
                End If


            End If
        End Sub
        Sub PhoneThread()
            'Dim ThreadsArray As List(Of Threading.Thread) = New List(Of Threading.Thread)
            Dim s As Integer
            'MsgBox(DT.Rows.Count)
            For s = 0 To DT.Rows.Count
                If s = DT.Rows.Count Then
                    s = 0
                Else
                    TextBox1.Text = DT.Rows(s)("Phone")
                    '   ThreadsArray.Add(t1)
                    Thread.Sleep(19)
                    'TextBox1.Text = s.ToString()
                    Me.Refresh()
                End If
            Next
        End Sub
 Private Sub BtnStart_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles BtnStart.Click
        Me.Close()

    End Sub