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我的程序需要一些帮助。当我使用自定义DayView 控件运行 VB.NET 程序时出现此错误。

************** 异常文本 ************** System.NullReferenceException：对象引用未设置为对象的实例。在 C:\Users\Daniel\My Programs\Visual Basic\SeaCow\SeaCow\SeaCow\Main.vb 中的 SeaCow.Main.DayView1_ResolveAppointments(Object sender, ResolveAppointmentsEventArgs args)：Calendar.DayView.OnResolveAppointments(ResolveAppointmentsEventArgs args) 中的第 120 行Calendar.DayView.OnPaint(PaintEventArgs e) 在 System.Windows.Forms.Control.PaintWithErrorHandling(PaintEventArgs e, Int16 层) 在 System.Windows.Forms.Control.WmPaint(Message& m) 在 System.Windows.Forms.Control.WndProc System.Windows.Forms.NativeWindow.Callback（IntPtr hWnd，Int32 msg，IntPtr wparam，IntPtr lparam）处的（消息和 m）

根据错误代码，下面的“for each”循环导致 NullReferenceException 错误。默认情况下，“约会”列表未分配任何内容，我找不到调用 ResolveAppointments 函数的位置。

    Private Sub DayView1_ResolveAppointments(ByVal sender As Object, ByVal args As Calendar.ResolveAppointmentsEventArgs) Handles DayView1.ResolveAppointments
    Dim m_Apps As New List(Of Calendar.Appointment)

    For Each m_App As Calendar.Appointment In appointments
        If (m_App.StartDate >= args.StartDate) AndAlso (m_App.StartDate <= args.EndDate) Then
            m_Apps.Add(m_App)
        End If
    Next

    args.Appointments = m_Apps
End Sub

这是 DayView.cs 控制文件中的OnResolveAppointments和ResolveAppointment函数。

public event EventHandler<ResolveAppointmentsEventArgs> OnResolveAppointments;



protected virtual void ResolveAppointments(ResolveAppointmentsEventArgs args)
    {
        System.Diagnostics.Debug.WriteLine("Resolve app");

        if (OnResolveAppointments != null)
            OnResolveAppointments(this, args);

        this.allDayEventsHeaderHeight = 0;

        // cache resolved appointments in hashtable by days.
        cachedAppointments.Clear();

        if ((selectedAppointmentIsNew) && (selectedAppointment != null))
        {
            if ((selectedAppointment.StartDate > args.StartDate) && (selectedAppointment.StartDate < args.EndDate))
            {
                args.Appointments.Add(selectedAppointment);
            }
        }

        foreach (Appointment appointment in args.Appointments)
        {
            int key = -1;
            AppointmentList list;

            if (appointment.StartDate.Day == appointment.EndDate.Day && appointment.AllDayEvent == false)
            {
                key = appointment.StartDate.Day;
            }
            else
            {
                key = -1;
            }

            list = (AppointmentList)cachedAppointments[key];

            if (list == null)
            {
                list = new AppointmentList();
                cachedAppointments[key] = list;
            }

            list.Add(appointment);
        }
    }

另外，这里是OnPaint方法

protected override void OnPaint(PaintEventArgs e)
    {
        e.Graphics.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.AntiAlias;

        // resolve appointments on visible date range.
        ResolveAppointmentsEventArgs args = new ResolveAppointmentsEventArgs(this.StartDate, this.StartDate.AddDays(daysToShow));
        ResolveAppointments(args);

        using (SolidBrush backBrush = new SolidBrush(renderer.BackColor))
            e.Graphics.FillRectangle(backBrush, this.ClientRectangle);

        // Visible Rectangle
        Rectangle rectangle = new Rectangle(0, 0, this.Width - VScrollBarWith, this.Height);

        DrawDays(ref e, rectangle);

        DrawHourLabels(ref e, rectangle);

        DrawDayHeaders(ref e, rectangle);
    }

有人有什么建议吗？

4

2 回答 2

1

DayView1_ResolveAppointments显然是控件事件的事件处理ResolveAppointments程序DayView1。如果For Each抛出异常，那么这意味着那appointments是Nothing在那个时候，而不是一个空列表，正如你所期望的那样。添加

If appointments Is Nothing Then
    Return
End If

在For Each循环之前。

于 2010-06-20T01:16:11.403 回答
0

您的控件似乎在其覆盖范围内Calendar.DayView调用了该函数。我建议你检查那里的代码。OnResolveAppointmentsOnPaint

同时，您可能只是跳过For Eachif appointmentsis Nothing。

于 2010-06-10T04:03:25.430 回答