Sharepoint WebPart Lifecycle Events

On Page Load
Constructor
OnInit
OnLoad
ConnectionConsumer method is called if web part is connectable (sets the connection providers interface in the webpart)
CreateChildControls
OnPreRender (if your web part is connectable you would typically call the connection provider here to retrieve data)
SaveViewState
Render
RenderChildren
RenderContents
On 1st Postback
(PostBack click handler sets ViewState via public Property)
Constructor
OnInit
CreateChildControls
OnLoad
PostBack click handling
ConnectionConsumer method is called if web part is connectable (sets the connection providers interface in the webpart)
OnPreRender (if your web part is connectable you would typically call the connection provider here to retrieve data)
SaveViewState
Render
RenderChildren
RenderContents
On 2nd Postback
(PostBack click handler sets ViewState via public Property)
Constructor
OnInit
LoadViewState
CreateChildControls
OnLoad
PostBack click handling
ConnectionConsumer method is called if web part is connectable (sets the connection providers interface in the webpart)
OnPreRender (if your web part is connectable you would typically call the connection provider here to retrieve data)
SaveViewState
Render
RenderChildren
RenderContents