动态添加控件

public partial class UserControl_Simulation_ProjectNeedsManagement : System.Web.UI.UserControl
{
    private ArrayList arrProjectID
    {
        get
        {
            if (ViewState["ControlCount"] == null)
                ViewState["ControlCount"] = new ArrayList();
            return (ArrayList)ViewState["ControlCount"];
        }
        set
        {
            ViewState["ControlCount"] = value;
        }
    }  
    protected void Page_Load(object sender, EventArgs e)
    {
        if (!IsPostBack)
        {
            ProjectBind();
        }
        foreach(int id in arrProjectID)
        {
            LoadUserControl(id);
        }  
    }
    protected void btnAddProject_Click(object sender, EventArgs e)
    {
        int id = Convert.ToInt16(ddlProjectSimulation.SelectedValue);
        if (!arrProjectID.Contains(id))
        {
            arrProjectID.Add(id);
            LoadUserControl(id);
        }
        else
        { 
        
        }
    }
    private void ProjectBind()
    {
        List<ProjectInfo> projInfoLi = ProjectList.GetAllSimulationProject();
        ddlProjectSimulation.DataSource = projInfoLi;
        ddlProjectSimulation.DataTextField = "ProjectName";
        ddlProjectSimulation.DataValueField = "ID";
        ddlProjectSimulation.DataBind();
    }

    private void LoadUserControl(int id)
    {
        UserControl_Simulation_JobFamilyNeedsManagement ucJobFamilyNeedsManagement = (UserControl_Simulation_JobFamilyNeedsManagement)LoadControl("JobFamilyNeedsManagement.ascx");
        ucJobFamilyNeedsManagement.ID = "ucjf" + id;
        ucJobFamilyNeedsManagement.ProjectInfo = ProjectList.GetSimulationProject(id);
        pan.Controls.Add(ucJobFamilyNeedsManagement);
    }
}

      动态添加控件，很多时候需要动态添加用户控件包括usercontrol或asp.net控件。但页面提交后我们要保持控件内容不变，可由于页面的执行顺序导致控件重新加载，数据丢失。

      由于页面viewstate tree保存是通过ID对应，所以我们在添加控件时可以给添加的控件加一个固定ID，然后存在viewstate中，每次页面加载时添加ID为这些的用户控件。如本例的代码中就是以projectid作为加载的usercontrol的固定id。

      加载usercontrol用loadcontrol（address）方法。