How to set minimum Size of Custom Control with "CreateParams"

Question

I am trying to make a draggable, resizable panel with a minimum size. I have used CreateParams for the Resize and now the Minimum size property doesn't work.

My question is how to set the minimum size in this case?

I have tried Limit resizable dimensions of a custom control (c# .net) but can't get it to work.

using System;
using System.Collections.Generic;
using System.Drawing;
using System.Linq;
using System.Reflection;
using System.Runtime.InteropServices;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace Move_Resize_Controls
{
    class MyPanel: Panel
    {
        // For Moving Panel "Drag the Titlebar and move the panel"
        public const int WM_NCLBUTTONDOWN = 0xA1;
        public const int HT_CAPTION = 0x2;

        [DllImportAttribute("user32.dll")]
        public static extern int SendMessage(IntPtr hWnd,
                         int Msg, int wParam, int lParam);
        [DllImportAttribute("user32.dll")]
        public static extern bool ReleaseCapture();

        // Constructor
        public MyPanel()
        {
            typeof(MyPanel).InvokeMember("DoubleBuffered", BindingFlags.SetProperty | BindingFlags.Instance | BindingFlags.NonPublic, null, this, new object[] { true }); // Double buffer MyPanel
            TitleBar(); // TitleBar
        }

        // Resize function for the panel - "Resizable Panel"
        protected override CreateParams CreateParams
        {
            get
            {
                var cp = base.CreateParams;
                cp.Style |= (int)0x00040000L;  // Turn on WS_BORDER + WS_THICKFRAME
                //cp.Style |= (int)0x00C00000L;  // Move
                return cp;
            }
        }

        // The Title Bar
        private void TitleBar()
        {
            Panel titleBar = new Panel();
            titleBar.BackColor = Color.Black;
            titleBar.Size = new Size(this.Size.Width, 20);
            titleBar.Dock = DockStyle.Top;
            this.Controls.Add(titleBar);

            titleBar.MouseDown  += new System.Windows.Forms.MouseEventHandler(this.MouseDownTitleBar); // Mouse Down - Event
            typeof(Panel).InvokeMember("DoubleBuffered", BindingFlags.SetProperty | BindingFlags.Instance | BindingFlags.NonPublic, null, titleBar, new object[] { true }); // Double Buffered 
        }

        // Move Panel
        private void MouseDownTitleBar(object sender, MouseEventArgs e)
        {
            if (e.Button == MouseButtons.Left)
            {
                ReleaseCapture();
                SendMessage(Handle, WM_NCLBUTTONDOWN, HT_CAPTION, 0);
            }
        }
    }
}

Answer 1

Set the MinimumSize() property to want you want for your control (as normal through the IDE or through code), then add the code below to your control to trap the WM_GETMINMAXINFO message and override the minimum size as the control is dynamically resized:

class MyPanel: Panel
{

    public const int WM_GETMINMAXINFO = 0x24;

    public struct POINTAPI
    {
        public Int32 X;
        public Int32 Y;
    }

    public struct MINMAXINFO
    {
        public POINTAPI ptReserved;
        public POINTAPI ptMaxSize;
        public POINTAPI ptMaxPosition;
        public POINTAPI ptMinTrackSize;
        public POINTAPI ptMaxTrackSize;
    }

    protected override void WndProc(ref Message m)
    {
        switch (m.Msg)
        {
            case WM_GETMINMAXINFO:
                MINMAXINFO mmi = (MINMAXINFO)System.Runtime.InteropServices.Marshal.PtrToStructure(m.LParam, typeof(MINMAXINFO));
                mmi.ptMinTrackSize.X = this.MinimumSize.Width;
                mmi.ptMinTrackSize.Y = this.MinimumSize.Height;
                System.Runtime.InteropServices.Marshal.StructureToPtr(mmi, m.LParam, true);
                break;
        }
        base.WndProc(ref m);
    }

}