如何从更新面板中的动态控件获取值 [英] How to get value from dynamic control in update panel

问题描述

我已经在下面给出了添加动态控件的代码，如何从这里获取值

 DropDownList ddlAgent =  new  DropDownList（）; 
 ddlAgent.EnableViewState =  false ; 
 ddlAgent.CssClass =   RegsSelect; 
 ddlAgent.ID =   ddlAgent; 
 ddlAgent.ClientIDMode = ClientIDMode.Static; 
 ddlAgent.Attributes.Add（  style，  margin-left：-4px; height：40px; width：328px;）; 
 upText.ContentTemplateContainer.Controls.Add（ddlAgent）; 
 
  //  使用下拉列表绑定数据 
 CUser objUser = < span class =code-keyword> new  CUser（）; 
 ddlAgent.DataSource = objUser.GetUserByRoleId（ 4 ）; 
 ddlAgent.DataValueField =   Id; 
 ddlAgent.DataTextField =   FirstName; 
 ddlAgent.DataBind（）; 

现在获取控制权

 DropDownList ddlAgent =（DropDownList）upText.ContentTemplateContainer.FindControl（  ddlAgent）; 

给出空参考例外



它是从上一个下拉列表的选定索引创建的，它放在updatepanel中

解决方案

始终在Page_Init事件中创建动态控件（阅读此内容 [ ^ ]和此 [ ^ ]获取详细信息）。

更改您的CS。试试这个：

  //  在此创建控件页面事件 
 受保护  void  Page_Init（ object  sender，EventArgs e）
 {
 DropDownList ddlAgent =  new  DropDownList（）; 
 ddlAgent.EnableViewState =  false ; 
 ddlAgent.CssClass =   RegsSelect; 
 ddlAgent.ID =   ddlAgent; 
 ddlAgent.ClientIDMode = ClientIDMode.Static; 
 ddlAgent.Attributes.Add（  style，  margin-left：-4px; height：40px; width：328px;）; 
 upText.ContentTemplateContainer.Controls.Add（ddlAgent）; 
} 

现在，找到控件并将其绑定在您的函数或方法中。试试这个：

 DropDownList ddlAgent =（DropDownList）upText.ContentTemplateContainer.FindControl（  ddlAgent）;  //  现在您将无法获得null referance异常 
  //  使用下拉列表绑定数据 
 CUser objUser =  new  CUser（）; 
 ddlAgent.DataSource = objUser.GetUserByRoleId（ 4 ）; 
 ddlAgent.DataValueField =   Id; 
 ddlAgent.DataTextField =   FirstName; 
 ddlAgent.DataBind（）; 

- Amit

I have given code for adding dynamic Control below , how to get value from this

DropDownList ddlAgent = new DropDownList();
                    ddlAgent.EnableViewState = false;
                    ddlAgent.CssClass = "RegsSelect";
                    ddlAgent.ID = "ddlAgent";
                    ddlAgent.ClientIDMode = ClientIDMode.Static;
                    ddlAgent.Attributes.Add("style", "margin-left:-4px;height:40px;width:328px;");
                    upText.ContentTemplateContainer.Controls.Add(ddlAgent);

                    //Binding data with dropdownlist
                    CUser objUser = new CUser();
                    ddlAgent.DataSource = objUser.GetUserByRoleId(4);
                    ddlAgent.DataValueField = "Id";
                    ddlAgent.DataTextField = "FirstName";
                    ddlAgent.DataBind();

now to get control

DropDownList ddlAgent=(DropDownList) upText.ContentTemplateContainer.FindControl("ddlAgent");

which gives Null Reference Exception

it is created from selected index of previous dropdownlist and it is placed in updatepanel

解决方案

Always create your dynamic control in Page_Init event (Read this[^] and this[^] for a detailed information).
Change your CS. Try this:

//Create the controls in this page event
protected void Page_Init(object sender, EventArgs e)
{
    DropDownList ddlAgent = new DropDownList();
    ddlAgent.EnableViewState = false;
    ddlAgent.CssClass = "RegsSelect";
    ddlAgent.ID = "ddlAgent";
    ddlAgent.ClientIDMode = ClientIDMode.Static;
    ddlAgent.Attributes.Add("style", "margin-left:-4px;height:40px;width:328px;");
    upText.ContentTemplateContainer.Controls.Add(ddlAgent);
}

Now, find the control and bind it in your function or method. Try this:

DropDownList ddlAgent=(DropDownList) upText.ContentTemplateContainer.FindControl("ddlAgent"); //Now you won't get a null referance exception
//Binding data with dropdownlist
CUser objUser = new CUser();
ddlAgent.DataSource = objUser.GetUserByRoleId(4);
ddlAgent.DataValueField = "Id";
ddlAgent.DataTextField = "FirstName";
ddlAgent.DataBind();

--Amit

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