Thay đổi trạng thái form c# (WindowState)

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

namespace _1_start { public partial class Form1 : Form { public Form1() { InitializeComponent(); }


    private void btnclose_Click(object sender, EventArgs e)
    {
        Close();
    }

    private void btnmini_Click(object sender, EventArgs e)
    {
        this.WindowState = FormWindowState.Minimized;
    }

    private void btnmax_Click(object sender, EventArgs e)
    {
        this.WindowState = FormWindowState.Maximized;
    }

    private void btntb_Click(object sender, EventArgs e)
    {
        this.WindowState = FormWindowState.Normal;
    }
}

}