Factory Pattern for User Controls
User Controls are handy when working in web forms, but what a mess they can generate. I was asked what to do when UCs are used and some dependencies need to be injected during the construction - but UCs are a bit tricky in regards to construction. So the possibilities are:
1. Use new operator and instantiate a user control (Web Application Project) - no good as the visual elements residing on the designer surface (.ascx) then not loaded.
2. Use Page.LoadControl(<path>) - but no option to pass in parameters.
3. Use Page.LoadControl(<type>, params object) - not strongly typed.
So all these possibilities are nice, but not helping to use a load with strongly typed parameters. Then the idea proposed at one of the replies with almost the same question was to use a static factory. I tried to play with the idea and this was a result.
Step 1 - create the UC
<%@ Control Language="C#" AutoEventWireup="true" CodeBehind="SomeUserControl.ascx.cs"
Inherits="LoadControlWithFactory.SomeUserControl" %>
<asp:TextBox runat="server" id="txtName"></asp:TextBox>
|
Step 2 - create the code behind with static factory method
1: public partial class SomeUserControl : UserControl 2: { 3: private string name; 4: 5: protected override void OnLoad(EventArgs e) 6: { 7: base.OnLoad(e); 8: txtName.Text = name; 9: } 10: 11: public static SomeUserControl Create(string name) 12: { 13: SomeUserControl some =
((Page)HttpContext.Current.Handler).LoadControl("~/SomeUserControl.ascx") as SomeUserControl; 14: some.name = name; 15: return some; 16: } 17: } |
Note: the underlined code has a bad smell - but that was the only idea I had to gain access to the currently executed page. Any other ideas are welcomed.
Step 3 - load UC dynamically through the code with injected data
1: public partial class _Default : System.Web.UI.Page 2: { 3: protected override void OnPreRender(EventArgs e) 4: { 5: base.OnPreRender(e); 6: phContent.Controls.Add(SomeUserControl.Create("Sean Feldman")); 7: phContent.Controls.Add(SomeUserControl.Create("Anna Feldman")); 8: } 9: } |
Conclusions
What it seems is that this allowed a few more things than just a pattern implementation. It allowed:
- DRY principle - rather than replicating the .ascx path wherever UC is loaded, this information is now stored and encapsulated inside the factory.
LoadControl("~/SomeUserControl.ascx") as SomeUserControl; // for Sean
LoadControl("~/SomeUserControl.ascx") as SomeUserControl; // for Sean
- Simplicity - Drop Dead Simple principle (well, this is something I like to apply recently to the code to make is easy to digest, so this is the name I came up with).
SomeUserControl.FactoryMethod(<typed params>); |
- Maintainability - simple and affordable.
Update 2007-12-17: I have re-arranged slightly the post to minimize clipping and attached the code.