带底边框的文本框

我希望有TextBox有底部边框，但绘制的图形为TextBox调整大小时会扭曲/损坏，因为Color.Transparent.

使用我找到的代码，我能够创建一个带下划线的文本框（具有透明顶部、左侧、右侧的绘制矩形）。问题是当我调整表单/窗口的大小时：当我将其调整为较小，然后再次调整大小以展开它时，绘制的图形会扭曲。有什么解决办法吗？

Here are photos: The second photo has been already resized smaller, then back to a larger size.

这是代码：

[DllImport("user32")]
    private static extern IntPtr GetWindowDC(IntPtr hwnd);
    struct RECT {
        public int left, top, right, bottom;
    }
    struct NCCALSIZE_PARAMS {
        public RECT newWindow;
        public RECT oldWindow;
        public RECT clientWindow;
        IntPtr windowPos;
    }

    float clientPadding = 0;
    int actualBorderWidth = 2;
    Color borderColor = Color.Black;
    protected override void WndProc(ref Message m) {
        //We have to change the clientsize to make room for borders
        //if not, the border is limited in how thick it is.
        if (m.Msg == 0x83) { //WM_NCCALCSIZE 
            if (m.WParam == IntPtr.Zero) {
                RECT rect = (RECT)Marshal.PtrToStructure(m.LParam, typeof(RECT));
                rect.left += 2;
                rect.right -= 2;
                rect.top += 0;
                rect.bottom -= 0;// (int)clientPadding;
                Marshal.StructureToPtr(rect, m.LParam, false);
            } else {
                NCCALSIZE_PARAMS rects = (NCCALSIZE_PARAMS)Marshal.PtrToStructure(m.LParam, typeof(NCCALSIZE_PARAMS));
                rects.newWindow.left += (int)clientPadding;
                rects.newWindow.right -= (int)clientPadding;
                rects.newWindow.top += (int)clientPadding;
                rects.newWindow.bottom -= 2;
                Marshal.StructureToPtr(rects, m.LParam, false);
            }
        }
        if (m.Msg == 0x85) {//WM_NCPAINT    
            IntPtr wDC = GetWindowDC(Handle);
            using (Graphics g = Graphics.FromHdc(wDC)) {
                ControlPaint.DrawBorder(g, new Rectangle(0, 0, Size.Width, Size.Height),
                    Color.Transparent, 1, ButtonBorderStyle.Solid,
                    Color.Transparent, 1, ButtonBorderStyle.Solid,
                    Color.Transparent, 1, ButtonBorderStyle.Solid,
                    borderColor, actualBorderWidth, ButtonBorderStyle.Solid);
            }
            return;
        }
        base.WndProc(ref m);
    }

EDIT :

I already found the issue, it's because of the Color.Transparent I fixed it by changing it to Color.White, since I have a white background. But then, that would not always be the case, how would I prevent that "Flickering/Tearing" while using Color.Transparent?

有一个TextBox带有底部边框，我可以提供的最简单的解决方法是将 1 像素高度的标签（或其他控件）停靠在底部TextBox:

using System.Drawing;
using System.Windows.Forms;
public class MyTextBox : TextBox
{
    public MyTextBox()
    {
        BorderStyle = System.Windows.Forms.BorderStyle.None;
        AutoSize = false; //Allows you to change height to have bottom padding
        Controls.Add(new Label()
                    { Height = 1, Dock = DockStyle.Bottom, BackColor = Color.Black });
    }
}