public class PageBase : System.Web.UI.Page
{
protected TMessageBox MsgBox;
override protected void OnInit(EventArgs e)
{
InitializeComponent();
base.OnInit(e);
}

private void InitializeComponent()
{
MsgBox = new TMessageBox(); //这一步成功
this.Controls.Add(MsgBox); //这一步的时候说MsgBox未定义
}
}