ASP.NET page life cycle

It is very much similar as ASP.NET page life cycle with enhancement of few events.

OnInit: This method handles initialization of the control.

OnLoad: This event handles the Load event and also used for initialize the control. But it is not intended for loading data or other processing functionality.

CreateChildControls: This creates any child controls.

EnsureChildControls: This method ensures that CreateChildControls has executed. EnsureChildControls method must be called to prevent null reference exceptions.

SaveViewState: View state of the web part saved.

OnPreRender: This method handles or initiates tasks such as data loading that must complete before the control can render.

Page.PreRenderComplete: The page fires the PreRenderComplete event after all controls have completed their OnPreRender methods.

Render: This method is used to render everything.

RenderContents: Renders the contents of the control only, inside of the outer tags and style properties.

OnUnload: Performs the final clean up.

Initial Load:

Events fired when a web part is initially loaded. 

Post-back:

     OnInit

     LoadViewState

     EnsureChildControls

     CreateChildControls

     EnsureChildControls

    CreateControlCollection

    EnsureChildControls (many)

    OnLoad

    btnUpdate_Click

    OnBubbleEvent

    EnsureChildControls

    OnPreRender

    EnsureChildControls (many)

    SaveViewState

    RenderControl

    Render

    RenderControl

    RenderContents

    RenderChildren

    OnUnload

    Dispose

Like Asp.Net life cycle there is also Web Part life cycle. So it is better to understand the web part life cycle. I’ve explained some of them which are used by every developer to cover most of the requirements:

OnInit: This method handles initialization of the control.

OnLoad: This event handles the Load event. This is also used for initialize the control but is not intended for loading data or other processing functionality.

CreateChildControls: This is the most popular event in web part life cycle. This creates any child controls. So if you are adding any control to display then you have to write in this method.

EnsureChildControls: This method ensures that CreateChildControls has executed. EnsureChildControls method must be called to prevent null reference exceptions.

SaveViewState: View state of the web part saved.

OnPreRender: This method handles or initiates tasks such as data loading that must complete before the control can render.

Page.PreRenderComplete: The page fires the PreRenderComplete event after all controls have completed their OnPreRender methods.

Render: This method is used to render everything.

RenderContents: Renders the contents of the control only, inside of the outer tags and style properties.

OnUnload: Performs the final cleanup.