从其他窗口中调用本窗口控件

//下面的代码是在别的窗体中调用Form3的ComboBox1控件
Form3 f3 = new Form3();
f3.ComboBox1.Items.Add("XXX");
 f3.Show();
//下面的代码是Form3 这个类
public partial class Form3 : Form
{
  ComboBox comboBox1 = null;
  public Form3()
  {
    InitializeComponent();
    comboBox1 = new ComboBox();
    comboBox1.FormattingEnabled = true;
    comboBox1.Location = new System.Drawing.Point(209, 84);
    comboBox1.Name = "comboBox1";
    comboBox1.Size = new System.Drawing.Size(121, 20);
    this.Controls.Add(comboBox1);
   }
  public ComboBox ComboBox1
  {
    get { return comboBox1; }
  }
}