在form中添加一个NotifyIcon控件
this.notifyIcon1 = new System.Windows.Forms.NotifyIcon(this.components);
notifyIcon1.Icon = new Icon("app.ico");//指定一个图标
notifyIcon1.Visible = false;
notifyIcon1.Click += new System.EventHandler(this.notifyIcon1_Click);
this.SizeChanged += new System.EventHandler(this.Form1_SizeChanged);