ASP Nested Tags in a Custom User Control

I wrote a blog post about this some time ago. In brief, if you had a control with the following markup:

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

You'd need the code in the control to be along the lines of:

[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; }}

I followed Rob's blog post, and made a slightly different control. The control is a conditional one, really just like an if-clause:

<wc:PriceInfo runat="server" ID="PriceInfo">    <IfDiscount>        You don't have a discount.    </IfDiscount>    <IfNotDiscount>        Lucky you, <b>you have a discount!</b>    </IfNotDiscount></wc:PriceInfo>

In the code I then set the HasDiscount property of the control to a boolean, which decides which clause is rendered.

The big difference from Rob's solution, is that the clauses within the control really can hold arbitrary HTML/ASPX code.

And here is the code for the control:

using System.ComponentModel;using System.Web.UI;using System.Web.UI.WebControls;namespace WebUtilities{    [ToolboxData("<{0}:PriceInfo runat=server></{0}:PriceInfo>")]    public class PriceInfo : WebControl, INamingContainer    {        private readonly Control ifDiscountControl = new Control();        private readonly Control ifNotDiscountControl = new Control();        public bool HasDiscount { get; set; }        [PersistenceMode(PersistenceMode.InnerProperty)]        [DesignerSerializationVisibility(DesignerSerializationVisibility.Content)]        public Control IfDiscount        {            get { return ifDiscountControl; }        }        [PersistenceMode(PersistenceMode.InnerProperty)]        [DesignerSerializationVisibility(DesignerSerializationVisibility.Content)]        public Control IfNotDiscount        {            get { return ifNotDiscountControl; }        }        public override void RenderControl(HtmlTextWriter writer)        {            if (HasDiscount)                ifDiscountControl.RenderControl(writer);            else                ifNotDiscountControl.RenderControl(writer);        }    }}

I ended up with something very similar to the answer by Rob (in wayback archive) @gudmundur-h, but I used ITemplate to get rid of that annoying "You can't place content between X tags" in the usage. I'm not entirely sure what is actually required or not, so it's all here just in case.

The partial/user control markup: mycontrol.ascx

Note the important bits: plcChild1 and plcChild2.

<!-- markup, controls, etc --><div class="shell">    <!-- etc -->    <!-- optional content with default, will map to `ChildContentOne` -->    <asp:PlaceHolder ID="plcChild1" runat="server">        Some default content in the first child.        Will show this unless overwritten.        Include HTML, controls, whatever.    </asp:PlaceHolder>    <!-- etc -->    <!-- optional content, no default, will map to `ChildContentTwo` -->    <asp:PlaceHolder ID="plcChild2" runat="server"></asp:PlaceHolder></div>

The partial/user control codebehind: mycontrol.ascx.cs

[ParseChildren(true), PersistChildren(true)][ToolboxData(false /* don't care about drag-n-drop */)]public partial class MyControlWithNestedContent: System.Web.UI.UserControl, INamingContainer {    // expose properties as attributes, etc    /// <summary>    /// "attach" template to child controls    /// </summary>    /// <param name="template">the exposed markup "property"</param>    /// <param name="control">the actual rendered control</param>    protected virtual void attachContent(ITemplate template, Control control) {        if(null != template) template.InstantiateIn(control);    }    [PersistenceMode(PersistenceMode.InnerProperty),    DesignerSerializationVisibility(DesignerSerializationVisibility.Content)]    public virtual ITemplate ChildContentOne { get; set; }    [PersistenceMode(PersistenceMode.InnerProperty), DesignerSerializationVisibility(DesignerSerializationVisibility.Content)]    public virtual ITemplate ChildContentTwo { get; set; }    protected override void CreateChildControls() {        // clear stuff, other setup, etc        // needed?        base.CreateChildControls();        this.EnsureChildControls(); // cuz...we want them?        // using the templates, set up the appropriate child controls        attachContent(this.ChildContentOne, this.plcChild1);        attachContent(this.ChildContentTwo, this.plcChild2);    }}

Important bits (?):

• ParseChildren -- so stuff shows up?
• PersistChildren -- so dynamically created stuff doesn't get reset?
• PersistenceMode(PersistenceMode.InnerProperty) -- so controls are parsed correctly
• DesignerSerializationVisibility(DesignerSerializationVisibility.Content) -- ditto?

The control usage

<%@ Register Src="~/App_Controls/MyStuff/mycontrol.ascx" TagPrefix="me" TagName="MyNestedControl" %><me:MyNestedControl SomeProperty="foo" SomethingElse="bar" runat="server" ID="meWhatever">    <%-- omit `ChildContentOne` to use default --%>    <ChildContentTwo>Stuff at the bottom! (not empty anymore)</ChildContentTwo></me:MyNestedControl>