C#

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

namespace TestWinFormControlLibrary
{
    public partial class UserControl1: UserControl
    {
        public UserControl1()
        {
            InitializeComponent();
        }
    }
}

public partial class CustomTextBoxForWhatever: TextBox

using System;
using System.Runtime.InteropServices;
using System.Text;

namespace FileINIAccess
{
    public class IniAccess
    {
        public string path;

        [DllImport("kernel32")] private static extern bool WritePrivateProfileSection(string lpAppName, string lpString, string lpFileName);
        [DllImport("kernel32")] private static extern bool WritePrivateProfileString(string section, string key, string val, string filePath);
        [DllImport("kernel32")] private static extern int GetPrivateProfileString(string section, string key, string def, StringBuilder retVal, int size, string filePath);
        [DllImport("kernel32")] private static extern int GetPrivateProfileSection (string lpAppName , StringBuilder lpReturnedString, int nSize , string lpFileName );

        public void IniFile(string INIPath)
        {
            path=INIPath;
        }

        public Boolean WriteProfileString(string Section, string Key, string Value)
        {
            bool rs=WritePrivateProfileString(Section,Key,Value,path);
            return rs;
        }

        public Boolean WritePrivatSection(string Section, string Value)
        {
            bool rs=WritePrivateProfileSection(Section,Value,path);
            return rs;
        }

        public string GetProfileString(string Section, string Key, string DefValue)
        {
            StringBuilder temp=new StringBuilder(255);
            int rs=GetPrivateProfileString(Section,Key,DefValue,temp,255,path);
            if (rs>0)
            {
                return temp.ToString();

            }
            else 
            {
                return DefValue.ToString();
            }
        }

        public string GetProfileSection(string Section)
        {
            StringBuilder temp=new StringBuilder(255);
            int rs = GetPrivateProfileSection(Section, temp, 255, path);
            if (rs>0)
            {
                return temp.ToString();
            }
            else 
            {
                return "";
            }
        }
    }

}

using Microsoft.VisualBasic;
using System;
using System.Collections;
using System.Collections.Generic;
using System.Data;
using System.Diagnostics;
using System.Runtime.InteropServices;

public class Form1
{

	private void Form1_Load(System.Object sender, System.EventArgs e)
	{
		CueBannerText.SetCueText(TextBox1, "Enter Name here");
	}
	public Form1()
	{
		Load += Form1_Load;
	}
}



public static class CueBannerText
{
	[DllImport("user32.dll", CharSet = CharSet.Auto)]
	private static Int32 SendMessage(IntPtr hWnd, int msg, int wParam, 	[MarshalAs(UnmanagedType.LPWStr)]
string lParam)
	{
	}
	[DllImport("user32", EntryPoint = "FindWindowExA", CharSet = CharSet.Ansi, SetLastError = true, ExactSpelling = true)]
	private static extern IntPtr FindWindowEx(IntPtr hWnd1, IntPtr hWnd2, string lpsz1, string lpsz2);

	private const int EM_SETCUEBANNER = 0x1501;

	public static void SetCueText(Control cntrl, string text)
	{
		if (cntrl is ComboBox) {
			IntPtr Edit_hWnd = FindWindowEx(cntrl.Handle, IntPtr.Zero, "Edit", null);
			if (!(Edit_hWnd == IntPtr.Zero)) {
				SendMessage(Edit_hWnd, EM_SETCUEBANNER, 1, text);
			}
		} else if (cntrl is TextBox) {
			SendMessage(cntrl.Handle, EM_SETCUEBANNER, 1, text);
		}
	}
}