In webform.aspx:  <cc:ctlB ID="ctl1" runat="server" Width="200px" />

If set value to width property, I will get a error that say ctlB.Page is null. This control will be fine with no width property, why?

Could anybody help me ? thanks

ctlA.cs
----------------------------
[
AspNetHostingPermission(SecurityAction.Demand, Level = AspNetHostingPermissionLevel.Minimal),
AspNetHostingPermission(SecurityAction.InheritanceDemand, Level = AspNetHostingPermissionLevel.Minimal),
DefaultProperty("Text"),
ValidationProperty("Text"),
ToolboxData("<{0}:ctlA runat=\"server\"> </{0}:ctlA>")
]
public class ctlA : WebControl, INamingContainer
{
   protected TextBox _textBox;
   protected HiddenField _hiddenBox;

   [Bindable(false), DefaultValue(""), TypeConverter(typeof(UnitConverter))]
   public override Unit Width
   {
       get
       {
           EnsureChildControls();
           return this._textBox.Width;
       }
       set
       {
           EnsureChildControls();
           this._textBox.Width = value;
       }
   }

   public override bool EnableViewState
   {
       get
       {
           EnsureChildControls();
           return this._textBox.EnableViewState;
       }
       set
       {
           EnsureChildControls();
           this._textBox.EnableViewState = value;
           this._hiddenBox.EnableViewState = value;
           this.EnableViewState = value;
       }
   }

   protected override void CreateChildControls()
   {
       this._textBox = new TextBox();
       this._textBox.ID = "Name";
       this._textBox.ReadOnly = this.ReadOnly;
       this._hiddenBox = new HiddenField();
       this._hiddenBox.ID = "Value";

       this.Controls.Add(this._textBox);
       this.Controls.Add(this._hiddenBox);
   }

   protected override void Render(HtmlTextWriter writer)
   {
       EnsureChildControls();
       base.Render(writer);
   }

   public override ControlCollection Controls
   {
       get
       {
           EnsureChildControls();
           return base.Controls;
       }
   }

   public ctlA()
       : base(HtmlTextWriterTag.Span)
   {
   }
}

--------------------------------------------------------------------------------

ctlB.cs
------------------------------

[ToolboxData("<{0}:ctlB runat=\"server\"> </{0}:ctlB>")]
public class ctlB : ctlA
{
   internal Image _schImage;

   public ctlB()
       : base()
   {
   }

   protected override void CreateChildControls()
   {
       base.CreateChildControls();

       this._schImage = new Image();
       this._schImage.ID = "imgButton";
       this._schImage.Attributes["align"] = "absmiddle";

       this._schImage.Attributes["onclick"] = String.Format("__OpenDialog('{0}', null, {1}, {2}, '{3}', '{4}', {5});",
       Page.ResolveUrl(this.DialogPagePath), this.DialogWidth.ToString(), this.DialogHeight.ToString(), this._textBox.ClientID, this._hiddenBox.ClientID, (this.DialogMode == DialogMode.Model) ? "true" : "false");

       this.Controls.Add(_schImage);
   }

   protected override void OnPreRender(EventArgs e)
   {
       base.OnPreRender(e);
       this.Page.ClientScript.RegisterClientScriptResource(this.GetType(), "OpenDialog.js");
   }

   public override ControlCollection Controls
   {
       get
       {
           EnsureChildControls();
           return base.Controls;
       }
   }
}