Life Cycle of a WebPart

1. OnInit - Handles the initialization of the webpart

2. OnLoad - Handles the load event

3. CreateChildControls - Creates all the child controls if present

4. EnsureChildControls - Ensures that the CreateChildControls method has been executed

5. OnPreRender - Handles tasks such as data loading etc that need to be completed before the controls are rendered

6. Page.PreRenderComplete - it is fired once the OnPreRender gets executed

7. Render - Renders the entire control

8. RenderContents - Renders the contents

Diff between Microsoft.SharePoint.WebPartPages and System.Web.UI.WebControls.WebParts

Microsoft.SharePoint.WebPartPages provides backward compatibility with the webparts of SharePoint 2003 in MOSS 2007.  In case we plan to create a webpart in MOSS 2007 with nothing to do with the previous versions, it's recommended to use System.Web.UI.WebControls.WebParts.

Types of WebParts

They can be braodly classified in to 2:

1. ASP .NET WebParts: These are built on top of the ASP .NET WebPart Infrastructure.  They need a reference to System.Web.dll and inherit from the webpart base class System.Web.UI.WebControls.WebParts namespace.  These can be used in ASP .NET applications as well as SharePoint sites.

2. SharePoint WebParts:  These need a reference from the Microsoft.SharePoint.dll and must inherit the base class Microsoft.SharePoint.WepPartPages namespace.  These can be used in Sharepoint Sites only.

Web Part description(.dwp) file

A Web Part description file is an XML text file with the extension .dwp. It can contain the following:

• Property names and settings for the instance of this Web Part.
• A reference to its companion Web Part assembly file (.dll).
• If a user has personalized a Web Part, changes to any common and custom property settings

When Windows SharePoint Services is first installed, a Web Part description file is often stored in the Site Web Part Gallery. Other instances of this Web Part description file are created over time as users export Web Parts, and as site administrators upload and download Web Parts.