如何从UserControl访问页面中的控件？

Question

如何从UserControl访问当前页面中的Control（下拉列表）？

在用户控件：

String test = ((DropDownList)this.Parent.FindControl("drpdwnlstMainRegion")).SelectedValue; 

或

String test = ((DropDownList)this.Page.FindControl("drpdwnlstMainRegion")).SelectedValue; 

它在（（DropDownList的）this.Parent.FindControl（ “drpdwnlstMainRegion”））由于某种原因，返回null？！？！

顺便说一句...我使用ASP.NET C＃3.5。

感谢

Answer 1

取决于你的页面的结构和控制的嵌套，你可能不得不递归遍历所有控件的抓取。像下面的内容可能会有所帮助：http://stevesmithblog.com/blog/recursive-findcontrol/

Answer 2

编译这些扩展方法到您的装配：

using System.Collections.Generic; 
using System.Linq; 
using System.Web.UI; 

public static class ControlExtensions 
{ 
    /// <summary> 
    /// Recurses through a control tree and returns an IEnumerable&lt;Control&gt; 
    /// containing all Controls from the control tree 
    /// </summary> 
    /// <returns>an IEnumerable&lt;Control&gt;</returns> 
    public static IEnumerable<Control> FindAllControls(this Control control) 
    { 
     yield return control; 

     foreach (Control child in control.Controls) 
      foreach (Control all in child.FindAllControls()) 
       yield return all; 
    } 

    /// <summary> 
    /// Recurses through a control tree and finds a control with 
    /// the ID specified 
    /// </summary> 
    /// <param name="control">The current object</param> 
    /// <param name="id">The ID of the control to locate</param> 
    /// <returns>A control of null if more than one control is found with a matching ID</returns> 
    public static Control FindControlRecursive(this Control control, string id) 
    { 
     var controls = from c in control.FindAllControls() 
         where c.ID == id 
         select c; 

     if (controls.Count() == 1) 
      return controls.First(); 

     return null; 
    } 
} 

然后用这样的：

Control whatYoureLookingFor = Page.Master.FindControlRecursive("theIdYouAreLookingFor"); 

这几个问题的重复已经在所以但我找不到它们。