在占位符内的UserControl中将值设置为TextBox

时间:2013-08-28 12:58:13

标签: asp.net user-controls placeholder

我在用户控件中有一个文本框。我创建了这个用户控件,并在占位符中加载。

但是当我尝试为文本框分配值时,我在下面提出错误:

Object reference not set to an instance of an object

这是用户控件:

<%@ Control Language="C#" AutoEventWireup="true" CodeBehind="IVT_FormClient.ascx.cs" Inherits="Evi.Sc.Web.Evi.IVT.Sublayouts.IVT_FormClient" %>
<asp:Panel ID="pnlContainer" runat="server">        
    <asp:TextBox ID="txtClientNumber" runat="server"></asp:TextBox>
</asp:Panel>

访问修饰符是(在用户控件中):

public string TxtFirstName
{
    get { return txtFirstName.Text; }
    set { txtFirstName.Text = value; }
}

在网络表单中,我有控件参考:

<%@ Reference Control="~/Evi/IVT/Sublayouts/IVT_FormClient.ascx"   %>

在用户控件的代码后面是:

    public partial class frm_VerifyIdentity : System.Web.UI.Page
    {
        IVT_FormClient ivtFormClient = new IVT_FormClient();

        protected void Page_Load(object sender, EventArgs e)
        {
            if (!IsPostBack)
            {
            IVT_FormClient ivtFormClient = (IVT_FormClient)LoadControl("~/Evi/IVT/Sublayouts/IVT_FormClient.ascx");

                Client UserClient = new Client();

                UserClient = Load_ClientVerification(Server.HtmlEncode(Request.QueryString["ID"]).Trim());

                if (UserClient != null)
                {
                    ivtFormClient.TxtFirstName = UserClient.FirstName;
                    plhFormClient.Controls.Add(ivtFormClient);
                }

            }
        }
 }

发生错误的是这行代码:

                ivtFormClient.TxtFirstName = UserClient.FirstName;

1 个答案:

答案 0 :(得分:0)

不要像UserControl那样在LoadControl通过构造函数创建实例,而是使用Page_Load创建实例。但是,您只是if(!IsPostBack)。因此,控件通过构造函数实例化下一个回发。

此外,您必须在每次回发时重新创建动态控件。我建议将UserControl delaratively添加到页面。您可以相应地隐藏/显示它。否则,您需要始终创建/添加它,最好是Page_Init而不是Page_Load

所以这不是最佳实践(只需将其添加到页面中),但应该按照需要运行:

IVT_FormClient ivtFormClient = null;

protected void Page_Init(object sender, EventArgs e)
{
    ivtFormClient =(IVT_FormClient)LoadControl("~/Evi/IVT/Sublayouts/IVT_FormClient.ascx");
    Client UserClient = new Client();
    UserClient = Load_ClientVerification(Server.HtmlEncode(Request.QueryString["ID"]).Trim());

    if (UserClient != null)
    {
        ivtFormClient.TxtFirstName = UserClient.FirstName;
        plhFormClient.Controls.Add(ivtFormClient);
    }
}