c# - 如何设置日期时间选择器下拉列表以仅显示月份

Question

因此，点击下拉菜单时不会显示这个。

我希望下拉菜单在点击时是这样的。

非常感谢您的帮助。 :)

Answer 1

使用 windows messages approach ，您可以检测月历控件显示和强制月 View ，您可以检测 View 更改并在月到日 View 更改时关闭月历控件(选择月份后)。

实现它的最简单方法是覆盖 DateTimePicker。

public class MonthPicker : DateTimePicker
{
    // initialize Format/CustomFormat to display only month and year.
    public MonthPicker()
    {
        Format = DateTimePickerFormat.Custom;
        CustomFormat = "MMMM yyyy";
    }

    // override Format to redefine default value (used by designer)
    [DefaultValue(DateTimePickerFormat.Custom)]
    public new DateTimePickerFormat Format
    {
        get => base.Format;
        set => base.Format = value;
    }

    // override CustomFormat to redefine default value (used by designer)
    [DefaultValue("MMM yyyy")]
    public new string CustomFormat
    {
        get => base.CustomFormat;
        set => base.CustomFormat = value;
    }

    protected override void WndProc(ref Message m)
    {
        if (m.Msg == WM_NOFITY)
        {
            var nmhdr = (NMHDR)Marshal.PtrToStructure(m.LParam, typeof(NMHDR));
            switch (nmhdr.code)
            {
                // detect pop-up display and switch view to month selection
                case -950:
                {
                    var cal = SendMessage(Handle, DTM_GETMONTHCAL, IntPtr.Zero, IntPtr.Zero);
                    SendMessage(cal, MCM_SETCURRENTVIEW, IntPtr.Zero, (IntPtr)1);
                    break;
                }

                // detect month selection and close the pop-up
                case MCN_VIEWCHANGE:
                {
                    var nmviewchange = (NMVIEWCHANGE)Marshal.PtrToStructure(m.LParam, typeof(NMVIEWCHANGE));
                    if (nmviewchange.dwOldView == 1 && nmviewchange.dwNewView == 0)
                    {
                        SendMessage(Handle, DTM_CLOSEMONTHCAL, IntPtr.Zero, IntPtr.Zero);
                    }

                    break;
                }
            }
        }
        base.WndProc(ref m);
    }

    private const int WM_NOFITY = 0x004e;
    private const int DTM_CLOSEMONTHCAL = 0x1000 + 13;
    private const int DTM_GETMONTHCAL = 0x1000 + 8;
    private const int MCM_SETCURRENTVIEW = 0x1000 + 32;
    private const int MCN_VIEWCHANGE = -750;

    [DllImport("user32.dll")]
    public static extern IntPtr SendMessage(IntPtr hWnd, int wMsg, IntPtr wParam, IntPtr lParam);

    [StructLayout(LayoutKind.Sequential)]
    private struct NMHDR
    {
        public IntPtr hwndFrom;
        public IntPtr idFrom;
        public int code;
    }

    [StructLayout(LayoutKind.Sequential)]
    struct NMVIEWCHANGE
    {
        public NMHDR nmhdr;
        public uint dwOldView;
        public uint dwNewView;
    }
}