Vb.net 如何从正在运行的倒计时计时器中减去时间？

基本上，我有一个计时器，在用户进行测试时从3分钟倒计时。如果用户跳过了一个问题，我希望受到15秒的惩罚。这样他们就少了15秒的完成时间。计时器在2点35分。用户点击skip，计时器下降到2:20，然后继续。这是我的密码：

Public Class Form1
    Private TargetDT As DateTime
    Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
        Me.AcceptButton = btnprocess
    End Sub
    Private Sub tmrCountdown_Tick(sender As Object, e As System.EventArgs) Handles tmrCountdown.Tick
        Dim ts As TimeSpan = TargetDT.Subtract(DateTime.Now)
        If ts.TotalMilliseconds > 0 Then
            lbltimer.Text = ts.ToString("mm\:ss")
        Else
            lbltimer.Text = "00:00"
            tmrCountdown.Stop()
            MessageBox.Show("Done")
        End If
    End Sub

    Private Sub btnskip_Click(sender As Object, e As EventArgs) Handles btnskip.Click
        ' This is where I want to subtract 15 seconds
        Dim ts As TimeSpan = TargetDT.Subtract(DateTime.Now.Add(TimeSpan.FromSeconds(15)))
    End Sub

    Private Sub btnbegin_Click(sender As Object, e As EventArgs) Handles btnbegin.Click
        tmrCountdown.Interval = 1
        TargetDT = DateTime.Now.Add(TimeSpan.FromMinutes(2.5))
        tmrCountdown.Start()
    End Sub
End Class

---

只需更改您的

TargetDT

值，以便在下一次

勾选事件中更新显示

我还将您的代码更改为使用
DateTime.UtcNow
而不是
DateTime。现在
聪明的用户无法更改时区以获得额外的时间（因为更改时区不需要管理/提升权限）

您也不需要指定超高的计时器频率（您已将其设置为每毫秒更新一次）。这是过分的。我将其设置为4Hz，这样屏幕上的显示不会滞后太多

Private Sub btnskip_Click(sender As Object, e As EventArgs) Handles btnskip.Click

    Me.TargetDT = Me.TargetDT.Subtract( TimeSpan.FromSeconds( 15 ) )

End Sub

Private Sub tmrCountdown_Tick(sender As Object, e As System.EventArgs) Handles tmrCountdown.Tick

    Dim now As DateTime = DateTime.UtcNow

    If now > Me.TargetDT Then

        Me.lbltimer.Text = "00:00"
        Me.tmrCountdown.Stop()
        MessageBox.Show("Done")

    Else

        Dim diff As TimeSpan = Me.TargetDT - now
        Me.lbltimer.Text = diff.ToString("mm\:ss")

    End If

End Sub

Private Sub btnbegin_Click(sender As Object, e As EventArgs) Handles btnbegin.Click

    Me.tmrCountdown.Interval = 250 ' no need to update more than 4 times a second
    Me.TargetDT = DateTime.UtcNow.Add( TimeSpan.FromMinutes(2.5) )

    Me.tmrCountdown.Start()
End Sub