先看下面的一个例子：
script runat="server" language="C#">
void Page_Load(Object sender, EventArgs e)
{ 
foreach(Control c in Controls) lblControlList.Text += c.ToString() + " - " + c.ID + "<br>";
}</script><html><head></head><body> <b>A List of the Controls in the <code>Controls</code> Collection</b><br> <asp:label runat="server" id="lblControlList" /> <p> <form runat="server"> What's your name? <asp:textbox runat="Server" id="txtName" /> </form></body></html>这个例子列出页面上所有的控件,结果如下：
A List of the Controls in the
Controls CollectionSystem.Web.UI.LiteralControl -
System.Web.UI.WebControls.Label - lblControlList
System.Web.UI.LiteralControl -
System.Web.UI.HtmlControls.HtmlForm -
System.Web.UI.ResourceBasedLiteralControl -
特别要注意的一点：以上代码没有列出ID=“txtName”的TextBox控件！因为这个TextBox控件包含在Form里面，是Form的一个子控件。而我们的代码 foreach(Control c in Controls) 只关心当前页面Controls的控件，至于子控件却未能涉及。（可以把这些控件理解成一个树状的层次关系）
页面Controls
/ | \ //foreach(Control c in Controls)
控件1 控件2 控件3 // 只判断控件1、2、3属于页面Controls
/ \ //而未涉及到下属子控件
子控件1 子控件2
为了真正做到遍历所有控件集，可以用递归的方法来实现：
<script runat="server" language="C#">
void IterateThroughChildren(Control parent) { foreach (Control c in parent.Controls)
{
lblControlList.Text += "<li>" + c.ToString() + "</li>"; if (c.Controls.Count > 0) // 判断该控件是否有下属控件。 { lblControlList.Text += "<ul>"; IterateThroughChildren(c); //递归，访问该控件的下属控件集。 lblControlList.Text += "</ul>";
} } } void Page_Load(Object sender, EventArgs e){ lblControlList.Text += "<ul>"; IterateThroughChildren(this); lblControlList.Text += "</ul>"; }</script><html><head></head><body> <b>A List of the Controls in the <code>Controls</code> Collection</b><br> <asp:label runat="server" id="lblControlList" /> <p> <form runat="server"> What's your name? <asp:textbox runat="Server" id="txtName" /> </form></body></html> 以上代码运行结果如下：A List of the Controls in the Controls Collection
- System.Web.UI.LiteralControl
- System.Web.UI.WebControls.Label
- System.Web.UI.LiteralControl
- System.Web.UI.HtmlControls.HtmlForm
- System.Web.UI.LiteralControl
- System.Web.UI.WebControls.TextBox
- System.Web.UI.LiteralControl
- System.Web.UI.ResourceBasedLiteralControl
这下TextBox控件真的露出了庐山真面目。