Web-Part life Cycle in SharePoint

On Page Load

1.Constructor

2.OnInit

3.OnLoad

4.ConnectionConsumer method is called if web part is connectable (sets the connection providers interface in the webpart)

5.CreateChildControls

6.OnPreRender (if your web part is connectable you would typically call the connection provider here to retrieve data)

7.SaveViewState

8.Render

9.RenderChildren

10.RenderContents

On 1st Postback

(PostBack click handler sets ViewState via public Property)

1.Constructor

2.OnInit

3.CreateChildControls

4.OnLoad

5.PostBack click handling

6.ConnectionConsumer method is called if web part is connectable (sets the connection providers interface in the webpart)

7.OnPreRender (if your web part is connectable you would typically call the connection provider here to retrieve data)

8.SaveViewState

9.Render

10.RenderChildren

11.RenderContents

On 2nd Postback

(PostBack click handler sets ViewState via public Property)

1.Constructor

2.OnInit

3.LoadViewState

4.CreateChildControls

5.OnLoad

6.PostBack click handling

7.ConnectionConsumer method is called if web part is connectable (sets the connection providers interface in the webpart)

8.OnPreRender (if your web part is connectable you would typically call the connection provider here to retrieve data)

9.SaveViewState

10.Render

11.RenderChildren

12.RenderContents

Note that during the 2nd postback, LoadViewState, is called, since in the 1st postback the click handler sets the value of the ViewState backed public property.