如何解决我的定时器算法问题？

Question

我希望找到此代码的问题，该代码给出了应用程序处于中断模式未处理的异常。我可以尝试什么？

System.InvalidOperationException occurred HResult=0x80131509 Message=An error occurred creating the form. See Exception.InnerException for details. The error >> > is: Object reference not set to an instance of an object. Inner Exception 1: NullReferenceException

代码：

Public Class Form1
    Dim h As Integer = 0, h2 As Integer = Val(TextBox1.Text)
    Dim m As Integer = 0, m2 As Integer = Val(TextBox2.Text)
    Dim s As Integer = 0, s2 As Integer = 60
    Dim m1 As Integer = 0, ml2 As Integer = 100

Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
        Timer2.Start()
    End Sub
Private Sub Button2_Click(sender As Object, e As EventArgs) Handles Button2.Click
        Timer2.Stop()
    End Sub

Private Sub Button3_Click(sender As Object, e As EventArgs) Handles Button3.Click
        Timer2.Stop()
        h2 = Val(TextBox1.Text)
        m2 = Val(TextBox2.Text)
        s2 = 60
        ml2 = 100
        Label1.Text = h2 & " : " & m2 & " : " & s2 & " : " & ml2
    End Sub

Private Sub Timer2_Tick(sender As Object, e As EventArgs) Handles Timer2.Tick
        ml2 -= 1
        Label1.Text = h2 & " : " & m2 & " : " & s2 & " : " & ml2
        If ml2 = 0 Then
            ml2 = 100
            s2 -= 1
            Label1.Text = h2 & " : " & m2 & " : " & s2 & " : " & ml2
            If s2 = 0 Then
                s2 = 60
                m2 -= 1
                Label1.Text = h2 & " : " & m2 & " : " & s2 & " : " & ml2
                If m2 = 0 Then
                    m2 = 60
                    h2 -= 1
                    Label1.Text = h2 & " : " & m2 & " : " & s2 & " : " & ml2
                    If h2 = 0 Then
                        h2 = 0
                        Timer1.Stop()
                        h2 = Val(TextBox1.Text)
                        m2 = Val(TextBox2.Text)
                        s2 = 60
                        ml2 = 100
                        Label1.Text = h2 & " : " & m2 & " : " & s2 & " : " & ml2
                    End If
                End If
            End If
        End If
    End Sub
End Class

Answer 1

在完成初始化之前，您无法访问 TextBox1 的值。只需稍微调整您的代码，错误就会消失。

Dim h As Integer = 0, h2 As Integer = 0
Dim m As Integer = 0, m2 As Integer = 0
Dim s As Integer = 0, s2 As Integer = 60
Dim m1 As Integer = 0, ml2 As Integer = 100

在窗体的加载事件中设置 h2 和 m2 值，如下所示：

Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load       
    h2 = Val(TextBox1.Text)
    m2 = Val(TextBox2.Text)
End Sub

如何解决我的定时器算法问题？

How can I fix my timer algorithm problem?

vb.net

timer

visual-studio-2017