C#タスクバーを除いたデスクトップのサイズを取得する。

namespace screensize;

public partial class Form1 : Form
{
    public Form1()
    {
        InitializeComponent();

        var btn = new Button
        {
            Location = new Point(100, 100),
            Size = new Size(400, 300),
            Text = "画面サイズを取得",
        };
        this.Controls.Add(btn);
        btn.Click += (s, e) => {
            if (Screen.PrimaryScreen is not null) {
                string msg = string.Format("WorkingArea Width:{0} Height:{1}\nBounds Width{2} Height{3}",
                    Screen.PrimaryScreen.WorkingArea.Width,
                    Screen.PrimaryScreen.WorkingArea.Height,
                    Screen.PrimaryScreen.Bounds.Width,
                    Screen.PrimaryScreen.Bounds.Height);
                MessageBox.Show(msg, "msg");
            }
        };
    }
}