TextBox with bottom border

Question

I want to have TextBox with bottom border but Graphics drawn for TextBox is distorted/broken on resize because of Color.Transparent.

Using an code I found, I was able to create a underlined TextBox (Drawn Rectangle with tranparent top, left, right). The problem is when I resize the form/window: when I resize it to smaller, then resize again to expand it, the graphics drawn is distorted. Any fix for this?

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

Here's the code:

[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?

Solution

To have a TextBox with bottom border, The most simple workaround that I can offer is docking a 1 pixel height lable (or other control) to bottom of the 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 });
    }
}

Comments

[Reza Aghaei]

@Yawz I saw your edit. You can use White color to render those invisible borders, but It also makes flickering when you move mouse over the control. Currently I prefer to use this workaround which I shared.

[Aesthetic]

This doesn't answer directly my question, but it's a solves my problem in a different approach, but how can I create a padding for the text? See this Screenshot: oi67.tinypic.com/10zvgqu.jpg I hope to give it padding on right and left sides, and a margin to raise the text..

[Reza Aghaei]

• For padding between Text and Line: it's enough to set AutoSize property in constructor to false. • For setting left padding and right padding, you should send EM_SETMARGINS message to the TextBox. You will find this post helpful: NumericUpDown with Unit I've set left padding in answer, and in comments added right padding too.

[Aesthetic]

I'm a newbie and literally don't know how to use that code to give my text box a left and right margin, anyways I will accept this. Here's my code where I don't know how to implement the left and right padding for the text.. pastebin.com/3AgtNZqx I am hoping for a result like this: imgur.com/2In0DQB .. I tried but I can't implement, I hope you have a solution for this..

[Aesthetic]

stackoverflow.com/questions/38448277/…

[Reza Aghaei]

The solution is the same way it's done in the numeric updown control which I linked to. That answer is really a good example and I hope you find it useful too. Anyway, I posted an answer for your new question :)

[HmH]

Nice and simple, but how can I change the label back color dynamically.

[Reza Aghaei]

@HmH TextBox.Controls[0] is the label. You can also create a public property to expose it.