1.示例代码，假如主窗体为MainForm,有三个子窗体分别是：Form1，Form2，Form3

public partial class MainForm : Form
{public MainForm(){InitializeComponent();}Form1 form1 = new Form1(); //子窗体1Form2 form2 = new Form2(); //子窗体2Form3 form3 = new Form3(); //子窗体3private void MainForm_Load(object sender, EventArgs e) //主窗体加载事件{ShowForm(form3);  //将窗体加载至panle控件中ShowForm(form2);ShowForm(form1);}private void ShowForm(Form frm) //显示子窗体{if (!splitContainer1.Panel2.Controls.Contains(frm)){frm.TopLevel = false; //窗体是否为顶级窗体frm.FormBorderStyle = FormBorderStyle.None; //设置窗体无边框// frm.Dock = DockStyle.Fill;     //设置填充方式为充满frm.Parent = this.splitContainer1.Panel2; //设置父窗体  随业务逻辑变动splitContainer1.Panel2.Controls.Add(frm);frm.Show();                    //打开窗体frm.BringToFront(); //将控件显示最前}else{frm.BringToFront();}}private void btnShowForm1_Click(object sender, EventArgs e) //切换子窗体1{ShowForm(form1);BackColorSet(((System.Windows.Forms.Button)sender).Text);}private void btnShowForm2_Click(object sender, EventArgs e) //切换子窗体2{ShowForm(form2);BackColorSet(((System.Windows.Forms.Button)sender).Text);}private void btnShowForm3_Click(object sender, EventArgs e) //切换子窗体3{ShowForm(form3);BackColorSet(((System.Windows.Forms.Button)sender).Text);}private void BackColorSet(string item)  //设置按钮背景色{//①现将所有的按钮统一赋值为同一种颜色this.btnShowForm1.BackColor = Color.Teal;this.btnShowForm2.BackColor = Color.Teal;this.btnShowForm3.BackColor = Color.Teal;//②根据传入的参数判断当前是哪个按钮按下switch (item){case "显示子窗体1":this.btnShowForm1.BackColor = Color.Red;break;case "显示子窗体2":this.btnShowForm2.BackColor = Color.Red;break;case "显示子窗体3":this.btnShowForm3.BackColor = Color.Red;break;default:break;}}
}

运行结果