Sweet DevTools

I just published few online tools for developers at devtools.manitra.net and I hope they will allow you to save time. The widgets currently available are :

Those tools already exist on the web but the key stuffs here is that they are :

  • tiny (minimalist web page without blabla about what a base64 encoding is etc ..)
  • embeddable as widget
  • free and ad-free

By the way, they are best used within a netvibes dashboard (Web Page Widget).

Enjoy :)

Code of duty : le concours de programmation de Criteo

Criteo, ma société, lance un concours de programmation avec 10 000€ ou 20 IPAD2 à gagner. Les short listés auront de grandes chances d’être embauchés.

Si vous en avez marre des SSII ou des sociétés qui ne jurent que par le prestige des diplômes et que, comme moi vous êtes passionnés par la programmation, c’est le moment de vous bouger et de rejoindre le petit Google français.

p.s : ce n’est pas un jeu vidéo :)

How to create deeply nested Asp.net Dynamic Controls ?

Creating controls at runtime (dynamic controls) in Asp.net is both tricky and unintuitive. This article will explain a pattern to make it easier.

The main advantages of this strategy are :
– ability to create deeply nested controls with unlimited depth
– each dynamicaly created controls have normal states (Viewstate is not broken)
– you can create those controls whenever you want (including OnClick events, PreRender and Render phases)
– no hacks with postback arguments are required

[UPDATE (2011/08/01)] : “M” found that the PersistentPanel doesn’t work well when it is instantiated in a markup file (aspx/ascx/master …) so I would advice you to instanciate it via code in the CreateChildControl method. The source code in the bottom of the page have been updated to reflect that.

The online demo

To help you understand what am I talking about here is an online example of deeply nested and dynamically created controls using Asp.Net.

You can create as much nested controls as you want and test that each controls persists its state upon postbacks.

The implementation

The PersistentPanel

The PersistentPanel is just a Panel wich persists its child controls collection using the viewstate automatically. This is a key control because it recreates the dynamically created controls on each post back during the right life-cycle phase : OnLoadViewstate. Thanks to this early recreation, those controls can persist their state in the ViewState like any controls declared in the markup page during the design time.

This kind of component is quite common now a days but the particularity here is that I do not try to persits all the nested controls but only the direct children. Indeed, if you try to persist and recreate the whole hierarchy, you’ll encounter problems and will have to handle a lot of special cases. More over since event handlers are not persisted, the restored components wont work.

The implementation process of the PersitentPanel :

  • during the save process of the viewstate we save the control hierarchy (type+Id only) using a serializable entity that store the control type, its Id and and a list of children
  • during the restore process of the viewstate we refill the Controls collection using the previously saved control hierarchy

The parent of the dynamic controls

The component wich will dynamicaly create the controls will first embed a PersistentPanel. And each time it will want to add a control it will add that control in the PersistentPanel’s controls collection. Here is an example :

Combining both to build a hierarchical data editor

Now we have a persistant panel and know that dynamically created controls are persisted, we’ll create a control that would create other complexes controls wich will have the same type as their creator. This would give us a powerfull control that would be able to display or edit hierarchical data wich, in our case, is a filter expression. We’ll have
– a control to edit scalar filter
– a control to edit composite filter
The scalar filter will just contain 3 simple controls for the field name, the operator and the value. The composite filter editor will be the interesting one. Indeed, it’s gonna contains a variable number of scalar editor and other composite filter editor. So it will use a persistant panel to host those nested controls. And that’s it !

Conclusion

The important things to remember are that :
– a control can be created at anytime, but it must be recreated on each postback during/before the LoadViewState of its container
– the ID of the dynamic control must be the same
– event handlers are not persisted, you have to rewire them up on each postback, the PersistantPanel has the ControlRestored event wich is the best place to do so.

Download the source code

The online demo application is available here :

Have fun !

Concise C# Part 3 : C# 3 shortcuts

The version 3 of C# brings us a lot of syntactic sugar to reduce the length of our code. Here are some of them.

This post is part of a serie about making C# code shorter.

Constructors with Property initializers

Collection initializers

Var keyword

Automatic properties

Concise C# Part 2 : Try Catch and reusability

Exception handling is an important part of any software. In this post, I will talk about a trick to make but some kind of reusability on exception handling.

This post is part of a serie about making C# code shorter

When you write code, you usually try to reuse your code by creating methods and calling those methods each time you the need their functionality. When working with exceptions, it’s a bit tricky because, they don’t follow the normal code flow, they jump out of your method … unless you catch them. The consequence is that you usually have multiple similar try {} catch {} blocks that are often copied and pasted.

This is what usually happens

The solution to reuse the exception block

This is what you could do to reuse the same error handling code block in c# :