C#

If you are showing a WinForm with 'WindowState = FormWindowState.Maximized, it will fill the screen completely, covering any TaskBars that are not hidden.

private void frmMain_Load(object sender, EventArgs e)
{
   MaximizedBounds = Screen.FromHandle(Handle).WorkingArea;
   WindowState = FormWindowState.Maximized;
}

Do you have experience with interop in C# using the Shell ... i.e., using WndProc, using P/Invokes ?

Ken Guru wrote:

If i set FormBorderStyle.Sizeable everything is OK.

Quote:

I drag the taskbar from the bottom to the side

using System;
using System.ComponentModel;
using System.Drawing;
using System.Windows.Forms;
using Microsoft.Win32;

namespace MaxonTBarChange
{
    public partial class Form1 : Form
    {
        public Rectangle AppBounds;

        public Form1()
        {
            InitializeComponent();

            AppBounds = Screen.PrimaryScreen.WorkingArea;

            this.Bounds = AppBounds;

            SystemEvents.UserPreferenceChanged += SystemEventsOnUserPreferenceChanged;

            this.Closing += OnClosing;
        }

        private void OnClosing(object sender, CancelEventArgs e)
        {
            SystemEvents.UserPreferenceChanged -= SystemEventsOnUserPreferenceChanged;
        }

        private void SystemEventsOnUserPreferenceChanged(object sender, UserPreferenceChangedEventArgs e)
        {
            // changing TaskBar location: category: 'Desktop
            // Console.WriteLine(e.Category.ToString());

            var bnds = Screen.PrimaryScreen.WorkingArea;

            if (AppBounds != bnds)
            {
                AppBounds = bnds;
                this.Bounds = AppBounds;
            }
        }
    }
}

string Display(object o)
{
    return o switch
    {   
        Point p => $"({p.X}, {p.Y})",
        _ => "unknown"
    };
}

OriginalGriff wrote:

Which means that we will have to deal with it as maintenance in future...

Bastard Programmer from Hell
If you can't read my code, try converting it here[^]
"If you just follow the bacon Eddy, wherever it leads you, then you won't have to think about politics." -- Some Bell.