c# - 使用 EnableVisualStyles 的 MonthCalendar 控件选择范围？

Question

我正在使用 MonthCalendar 控件并希望以编程方式选择一个日期范围。当我这样做时，如果调用了 Application.EnableVisualStyles()，控件将无法正确绘制。根据 MSDN，这是一个已知问题。

Using the MonthCalendar with visual styles enabled will cause a selection range for the MonthCalendar control to not paint correctly (from: http://msdn.microsoft.com/en-us/library/system.windows.forms.monthcalendar.aspx)

除了不调用 EnableVisualStyles 之外真的没有解决办法吗？这似乎使该特定控件对于一系列应用程序完全无用，并且从我的角度来看是相当明显的疏忽。

Answer 1

在寻找相同问题的解决方案时，我首先在这里遇到这个问题，但后来我发现了 Nicke Andersson 的博客条目.我发现这很有帮助。这是我对 Nicke 的例子所做的:

public class MonthCalendarEx : System.Windows.Forms.MonthCalendar
{
    private int _offsetX;
    private int _offsetY;
    private int _dayBoxWidth;
    private int _dayBoxHeight;

    private bool _repaintSelectedDays = false;

    public MonthCalendarEx() : base()
    {
        OnSizeChanged(null, null);
        this.SizeChanged += OnSizeChanged;
        this.DateChanged += OnSelectionChanged;
        this.DateSelected += OnSelectionChanged;
    }

    protected static int WM_PAINT = 0x000F;

    protected override void WndProc(ref System.Windows.Forms.Message m)
    {
        base.WndProc(ref m);
        if (m.Msg == WM_PAINT)
        {
            Graphics graphics = Graphics.FromHwnd(this.Handle);
            PaintEventArgs pe = new PaintEventArgs(
                graphics, new Rectangle(0, 0, this.Width, this.Height));
            OnPaint(pe);
        }
    }

    private void OnSelectionChanged(object sender, EventArgs e)
    {
        _repaintSelectedDays = true;
    }

    private void OnSizeChanged(object sender, EventArgs e)
    {                         
        _offsetX = 0;
        _offsetY = 0;

        // determine Y offset of days area 
        while (
            HitTest(Width / 2, _offsetY).HitArea != HitArea.PrevMonthDate &&
            HitTest(Width / 2, _offsetY).HitArea != HitArea.Date)
        {
            _offsetY++;
        }

        // determine X offset of days area 
        while (HitTest(_offsetX, Height / 2).HitArea != HitArea.Date)
        {
            _offsetX++;
        }

        // determine width of a single day box
        _dayBoxWidth = 0;
        DateTime dt1 = HitTest(Width / 2, _offsetY).Time;

        while (HitTest(Width / 2, _offsetY + _dayBoxHeight).Time == dt1)
        {
            _dayBoxHeight++;
        }

        // determine height of a single day box
        _dayBoxWidth = 0;
        DateTime dt2 = HitTest(_offsetX, Height / 2).Time;

        while (HitTest(_offsetX + _dayBoxWidth, Height / 2).Time == dt2)
        {
            _dayBoxWidth++;
        }
    }

    protected override void OnPaint(PaintEventArgs e)
    { 
        base.OnPaint(e);

        if (_repaintSelectedDays)
        {
            Graphics graphics = e.Graphics;
            SelectionRange calendarRange = GetDisplayRange(false);
            Rectangle currentDayFrame = new Rectangle(
                -1, -1, _dayBoxWidth, _dayBoxHeight);

            DateTime current = SelectionStart;
            while (current <= SelectionEnd)                
            {
                Rectangle currentDayRectangle;

                using (Brush selectionBrush = new SolidBrush(
                    Color.FromArgb(
                        255, System.Drawing.SystemColors.ActiveCaption))) 
                {                    
                    TimeSpan span = current.Subtract(calendarRange.Start); 
                    int row = span.Days / 7; 
                    int col = span.Days % 7; 

                    currentDayRectangle = new Rectangle(
                        _offsetX + (col + (ShowWeekNumbers ? 1 : 0)) * _dayBoxWidth, 
                        _offsetY + row * _dayBoxHeight, 
                        _dayBoxWidth, 
                        _dayBoxHeight);

                    graphics.FillRectangle(selectionBrush, currentDayRectangle); 
                }

                TextRenderer.DrawText(
                    graphics, 
                    current.Day.ToString(), 
                    Font, 
                    currentDayRectangle, 
                    System.Drawing.SystemColors.ActiveCaptionText, 
                    TextFormatFlags.HorizontalCenter | TextFormatFlags.VerticalCenter);

                if (current == this.TodayDate)
                {
                    currentDayFrame = currentDayRectangle;
                }

                current = current.AddDays(1);
            }

            if (currentDayFrame.X > 0)
            {
                graphics.DrawRectangle(new Pen(
                    new SolidBrush(Color.Red)), currentDayFrame);
            }

            _repaintSelectedDays = false;
        }
    }
}