C# 、子窗体调用父窗体属性、方法

namespace Test
{
    public partial class FrmMain : Form
    {
        public FrmMain()
        {
             InitializeComponent();
        }
        public DataTable DT;
        private void button1_Click(object sender, EventArgs e) 
        { 
            FrmChild fm = new FrmOptime(this); 
            fm.Show(); 
         } 
        public void BindData(){}
     }
}

namespace Test
{
    public partial class FrmChild : Form
    {
        public FrmChild ()
        {
            InitializeComponent();
        }
        FrmMain frmMain;
        public FrmChild (FrmMain fm)
        {
            InitializeComponent();
            frmMain = fm;
        }
    private void button1_Click(object sender, EventArgs e) 
    { 
        frmMain.RemnantDT;
        frmMain.BindData();
    }
   }
}