DockPanel 子窗体如何在父窗体打开另一子窗体，以选项卡式存在

父窗体代码：

//dockPanel1为DockPanel的实例
FrmOption frmOption = new FrmOption(dockPanel1);
frmOption.Show(dockPanel1);

子窗体代码:

public partial class FrmOption : DockContent
{
    private readonly DockPanel dockPanel1 = new DockPanel();

    public FrmOption(DockPanel dockPanel1)
    {
        InitializeComponent();
        this.dockPanel1 = dockPanel1;
    }

    private void FrmOption_Load(object sender, EventArgs e)
    {
        //调用父窗体的ToolStripProgressBar ,在父窗体ToolStripProgressBar 
必须设置为Modifier=Internal以上级别
        ToolStripProgressBar toolStripProgressBar = ((MainForm)MdiParent).toolStripProgressBar;
        toolStripProgressBar.Visible = true;
        toolStripProgressBar.Value = 90;
    }

    private void button1_Click(object sender, EventArgs e)
    {
        MainForm mainForm = MdiParent as MainForm;
        foreach (Form child in mainForm.MdiChildren)
        {
            //此处将在父窗体选项卡上显示
            if (child.Name == "FrmDepartment")
            {
                child.Activate();
                return;
            }
        }
        FrmDepartment frm = new FrmDepartment();
        frm.Show(dockPanel1);
    }
}