Within each stage of the life cycle of a page, the page raises events that you can handle to run your own code.The following are the page life-cycle events that you will use most frequently.
- Control events
Use this event for the following:
Check the IsPostBack property to determine whether this is the first time the page is being processed.
Create or re-create dynamic controls.
Set a master page dynamically.
Set the Theme property dynamically.
Read or set profile property values.
Note: If the request is a postback, the values of the controls have not yet been restored from view state. If you set a control property at this stage, its value might be overwritten in the next event.
Raised after all controls have been initialized and any skin settings have been applied. Use this event to read or initialize control properties.
Raised by the Page object. Use this event for processing tasks that require all initialization be complete.
Use this event if you need to perform processing on your page or control before the Load event.
After the Page raises this event, it loads view state for itself and all controls, and then processes any postback data included with the Request instance.
The Page calls the OnLoad event method on the Page, then recursively does the same for each child control, which does the same for each of its child controls until the page and all controls are loaded.
Use the OnLoad event method to set properties in controls and establish database connections.
6). Control events:
Use these events to handle specific control events, such as a Button control's Click event or a TextBox control's TextChanged event.
Note: In a postback request, if the page contains validator controls, check the IsValid property of the Page and of individual validation controls before performing any processing.
Use this event for tasks that require that all other controls on the page be loaded.
Before this event occurs:
The Page object calls EnsureChildControls for each control and for the page.
Each data bound control whose DataSourceID property is set calls its DataBind method.
The PreRender event occurs for each control on the page. Use the event to make final changes to the contents of the page or its controls.
Before this event occurs, ViewState has been saved for the page and for all controls. Any changes to the page or controls at this point will be ignored.
Use this event perform tasks that require view state to be saved, but that do not make any changes to controls.
This is not an event; instead, at this stage of processing, the Page object calls this method on each control. All ASP.NET Web server controls have aRender method that writes out the control's markup that is sent to the browser.
If you create a custom control, you typically override this method to output the control's markup. However, if your custom control incorporates only standard ASP.NET Web server controls and no custom markup, you do not need to override the Render method.
A user control (an .ascx file) automatically incorporates rendering, so you do not need to explicitly render the control in code.
This event occurs for each control and then for the page. In controls, use this event to do final cleanup for specific controls, such as closing control-specific database connections.
For the page itself, use this event to do final cleanup work, such as closing open files and database connections, or finishing up logging or other request-specific tasks.
Note: During the unload stage, the page and its controls have been rendered, so you cannot make further changes to the response stream. If you attempt to call a method such as the Response.Write method, the page will throw an exception.