How to add child nodes to custom asp.net user control derived from System.Web.UI.Control

Question

I would like to know how to add some additional child nodes to a custom user control class derived from System.Web.UI.Control.

For example currently I have a control that contains no child nodes and on the design surface looks like the following.

<cust:MyCustomControl id="ctlMyCustomControl" runat="server" attribute1="somevalue" attribute2="somevalue" ></MyCustomControl>

What I am looking for is to have the ability to add n number of child nodes to this control from the design surface and then access their values from the code. So adding to the control stated above.

<cust:MyCustomControl id="ctlMyCustomControl" runat="server" attribute1="somevalue" attribute2="somevalue" >
  <childnode1>value1</childnode1>
  <childnode2>value2</childnode2>
</MyCustomControl>

It is not clear to me how to access the child nodes.

Any insight on how to do this is appreciated.

Answer 1

You want to be able to describe asp.net control properties declaratively.

To be able to have the following markup:

<Abc:CustomControlUno runat="server" ID="Control1">
    <Children>
        <Abc:Control1Child IntegerProperty="1" StringProperty="Item1" />
        <Abc:Control1Child IntegerProperty="2" StringProperty="Item2" />
    </Children>
</Abc:CustomControlUno>

You need the following code:

[ParseChildren(true)]
[PersistChildren(true)]
[ToolboxData("<{0}:CustomControlUno runat=server></{0}:CustomControlUno>")]
public class CustomControlUno : WebControl, INamingContainer
{
    private Control1ChildrenCollection _children;

    [PersistenceMode(PersistenceMode.InnerProperty)]
    [DesignerSerializationVisibility(DesignerSerializationVisibility.Content)]
    public Control1ChildrenCollection Children
    {
        get
        {
            if (_children == null)
                _children = new Control1ChildrenCollection();
            return _children;
        }
    }
}

public class Control1ChildrenCollection : List<Control1Child>
{
}

public class Control1Child
{

    public int IntegerProperty { get; set; }
    private string StringProperty { get; set; }
}

Answer 2

If you wanted to support the given syntax as-is (without having to use the tag prefixes), you could use a ControlBuilder:

 //MyControlBuilder 
 public class MyControlBuilder : ControlBuilder
 {
   public override Type GetChildControlType(string tagName, IDictionary attribs)
   { 
     if (tagName.StartsWith("childnode")) return typeof(Control);
     else return base.GetChildControlType(tagName,attribs);
   }

   public override void AppendLiteralString(string s)
   { 
     //ignore literals betwen tags
   }
 }

 //MyCustomControl
 [ParseChildren(false)]
 [ControlBuilder(typeof(MyControlBuilder))]
 public class MyCustomControl : Control
 {
   public string attribute1 {get;set;}
   public string attribute2 {get;set;}

   protected override void AddParsedSubObject(object obj)
   {
     Control ctrl = (Control) obj;
     LiteralControl childNode = ctrl.Controls[0];

     //Add as-is (e.g., literal "value1")
     Controls.Add(childNode);
   }
 }

See also http://msdn.microsoft.com/en-us/library/system.web.ui.controlbuilder.aspx