单击“添加”按钮后如何重新加载动态添加的用户控件

Question

我有一个要求，当我单击父页面中的“添加”按钮时，必须动态加载用户控件。 用户控件包含文本框，下拉菜单和删除按钮。 如果单击特定用户控件的“删除”按钮，它将被删除。 一切都很好。 问题是，单击“添加”按钮后，页面将回退，并且用户控件中的选定值将失去其值。 我需要一种方法来从Code后面获取所有动态添加的控件，并将其存储在视图状态中，然后在页面加载中再次将其转换为用户控件，并将其添加到页面中。 请对此提供帮助。

SecondaryDestination.ascx如下所示：占位符将动态加载控件。

<td><asp:Label id="lblSecondary">Secondary Destination</asp:Label></td>     
<td>asp:DropDownList id="ddlSecondary" runat="server" CssClass="ddlbox" AutoPostBack="true"></asp:DropDownList> </td>   
<asp:UpdatePanel ID="updateEmailFtp" runat="server" UpdateMode="Conditional">
<ContentTemplate>
    <asp:PlaceHolder ID="plcEmail" runat="server">
        <table cellpadding="0" cellspacing="0" border="0" class="tbl_form" runat="server" id="tblSecondary">
        </table>    
    </asp:PlaceHolder>
</ContentTemplate>
<Triggers>
    <asp:AsyncPostBackTrigger ControlID="ddlSecondary" EventName="SelectedIndexChanged" />
</Triggers>

用户控件动态添加控件

protected void ddlSecondary_SelectedIndexChanged(object sender, EventArgs e)
    {
        if(ddlSecondary.SelectedIndex > 0)
        {
            pickerSecondaryViewPresenter = new PickerSecondaryViewPresenter(this);
            DestinationBO secondaryDestination = pickerSecondaryViewPresenter.getSecondaryDestination(int.Parse(ddlSecondary.SelectedItem.Value));

            if(secondaryDestination.DestinationType == "Email")
            {
                HtmlTable tblContent = (HtmlTable)FindControl("tblSecondary");

                Label lblPrimary = new Label();                 
                lblPrimary.Text = "Email Disstribution List";                                       
                HtmlTableCell tcPrimary1 = new HtmlTableCell();
                tcPrimary1.Controls.Add(lblPrimary);

                Label lblPrimaryDistributionList = new Label(); 
                lblPrimaryDistributionList.Text = secondaryDestination.DistributionList;
                HtmlTableCell tcPrimary2 = new HtmlTableCell();
                tcPrimary2.Controls.Add(lblPrimaryDistributionList);

                HtmlTableRow trPrimary = new HtmlTableRow();
                trPrimary.Controls.Add(tcPrimary1);
                trPrimary.Controls.Add (tcPrimary2);                        
                tblContent.Controls.Add(trPrimary);                     
            }
            else
            {
                Label lblFtp = new Label();                 
                lblFtp.Text = "Ftp Host";
                HtmlTableCell tcPrimary1 = new HtmlTableCell();
                tcPrimary1.Controls.Add(lblFtp);

                Label lblFtpHost = new Label();                 
                lblFtpHost.Text = secondaryDestination.FtpHost;                 
                HtmlTableCell tcPrimary2 = new HtmlTableCell();
                tcPrimary2.Controls.Add(lblFtpHost);    

                Button btn = new Button();
                btn.Text = "Connect FTP";
                tcPrimary2.Controls.Add(btn);   

                HtmlTableRow trPrimary1 = new HtmlTableRow();
                trPrimary1.Controls.Add(tcPrimary1);
                trPrimary1.Controls.Add (tcPrimary2);   

                Label lblDirectory = new Label();                   
                lblDirectory.Text = "Ftp Directory";
                HtmlTableCell tcPrimary3 = new HtmlTableCell();
                tcPrimary3.Controls.Add(lblDirectory);

                TextBox txtDirectory = new TextBox();                   
                txtDirectory.Text = "";                 
                HtmlTableCell tcPrimary4 = new HtmlTableCell();
                tcPrimary4.Controls.Add(txtDirectory);

                HtmlTableRow trPrimary2 = new HtmlTableRow();
                trPrimary2.Controls.Add(tcPrimary3);
                trPrimary2.Controls.Add(tcPrimary4);

                tblSecondary.Controls.Add(trPrimary1);      
                tblSecondary.Controls.Add(trPrimary2);

            }

此用户控件将添加到page1.aspx中：

<div>
<asp:UpdatePanel id ="up1" UpdateMode="conditional">
    <ContentTemplate>
        <uc:DestinationPicker id="destinatioPicker" runat="server" ></uc:DestinationPicker>
    </ContentTemplate>
</asp:UpdatePanel>
</div>
<asp:PlaceHolder ID="divSecondary" runat="server">  
    <ucS:DestinationPickerSecondary id="destinationPickerSecondary" runat="server" ></ucS:DestinationPickerSecondary>       
</asp:PlaceHolder>  

<div>
    <asp:Button id="btnAddSecondary" Text="Add Secondary" runat="server" OnClick="btnAddSecondary_Click"></asp:Button>
</div>

</div>

添加和删​​除用户控件可以正常工作：

protected void Page_Load(object sender, EventArgs e)
{    if(IsPostBack)
{
    AddAndRemoveDynamicControls();
}
}

我的问题是，每次单击添加按钮以添加动态添加的用户控件的新实例时，我都需要将所选项目保存在先前添加的用户控件的下拉列表中

Answer 1

在回发处理期间加载viewstate时，它将视图状态中的值与已加载的控件相关联。 您必须在处理viewstate之前动态地重新加载控件。 我过去在page_init事件中完成了此操作。