不能在调整无边界表单大小的同时绘制边界

Question

我有一个无边界的表单（FormBorderStyle.None）...我试图覆盖WndProc方法来调整无边界表单的大小，并使用OnPaint方法在表单周围绘制边界线...

但是当我调整表单大小时，左右边框的边界线不可见。

当您打开Windows照片应用程序时，您可以在照片应用程序周围看到一个蓝色边框...我要绘制一个这样的边框。

我的完整代码：

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace ModernBorderlessForm
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();

            this.BackColor = Color.FromArgb(63, 63, 63);
            this.FormBorderStyle = FormBorderStyle.None;
            this.DoubleBuffered = true;
            this.SetStyle(ControlStyles.ResizeRedraw, true);
        }

        private const int
            HTLEFT = 10,
            HTRIGHT = 11,
            HTTOP = 12,
            HTTOPLEFT = 13,
            HTTOPRIGHT = 14,
            HTBOTTOM = 15,
            HTBOTTOMLEFT = 16,
            HTBOTTOMRIGHT = 17;
        const int _ = 10; // you can rename this variable if you like

        new Rectangle Top { get { return new Rectangle(0, 0, this.ClientSize.Width, _); } }
        new Rectangle Left { get { return new Rectangle(0, 0, _, this.ClientSize.Height); } }
        new Rectangle Bottom { get { return new Rectangle(0, this.ClientSize.Height - _, this.ClientSize.Width, _); } }
        new Rectangle Right { get { return new Rectangle(this.ClientSize.Width - _, 0, _, this.ClientSize.Height); } }
        Rectangle TopLeft { get { return new Rectangle(0, 0, _, _); } }
        Rectangle TopRight { get { return new Rectangle(this.ClientSize.Width - _, 0, _, _); } }
        Rectangle BottomLeft { get { return new Rectangle(0, this.ClientSize.Height - _, _, _); } }
        Rectangle BottomRight { get { return new Rectangle(this.ClientSize.Width - _, this.ClientSize.Height - _, _, _); } }

        // For resizing borderless form
        protected override void WndProc(ref Message message)
        {
            base.WndProc(ref message);

            if (message.Msg == 0x84) // WM_NCHITTEST
            {
                var cursor = this.PointToClient(Cursor.Position);

                if (TopLeft.Contains(cursor)) message.Result = (IntPtr)HTTOPLEFT;
                else if (TopRight.Contains(cursor)) message.Result = (IntPtr)HTTOPRIGHT;
                else if (BottomLeft.Contains(cursor)) message.Result = (IntPtr)HTBOTTOMLEFT;
                else if (BottomRight.Contains(cursor)) message.Result = (IntPtr)HTBOTTOMRIGHT;

                else if (Top.Contains(cursor)) message.Result = (IntPtr)HTTOP;
                else if (Left.Contains(cursor)) message.Result = (IntPtr)HTLEFT;
                else if (Right.Contains(cursor)) message.Result = (IntPtr)HTRIGHT;
                else if (Bottom.Contains(cursor)) message.Result = (IntPtr)HTBOTTOM;
            }
        }

        // For drawing border lines
        protected override void OnPaint(PaintEventArgs e)
        {
            base.OnPaint(e);
            e.Graphics.DrawRectangle(Pens.DodgerBlue, 0, 0, this.ClientSize.Width - 1, this.ClientSize.Height - 1);
        }
    }
}