When an ASP.NET page runs, the page goes through a life cycle in which it performs a series of processing steps. These include initialization, instantiating controls, restoring and maintaining state, running event handler code, and rendering. It is important for you to understand the page life cycle so that you can write code at the appropriate life-cycle stage for the effect you intend.

If you develop custom controls, you must be familiar with the page life cycle in order to correctly initialize controls, populate control properties with view-state data, and run control behavior code. The life cycle of a control is based on the page life cycle, and the page raises many of the events that you need to handle in a custom control.

This topic contains the following sections:

• General Page Life-cycle Stages

• Life-cycle Events

• Additional Page Life Cycle Considerations

• Catch-Up Events for Added Controls

• Data Binding Events for Data-Bound Controls

• Login Control Events

General Page Life-Cycle Stages

In general terms, the page goes through the stages outlined in the following table. In addition to the page life-cycle stages, there are application stages that occur before and after a request but are not specific to a page. For more information, see Introduction to the ASP.NET Application Life Cycle and ASP.NET Application Life Cycle Overview for IIS 7.0.

Some parts of the life cycle occur only when a page is processed as a postback. For postbacks, the page life cycle is the same during a partial-page postback (as when you use an UpdatePanel control) as it is during a full-page postback.

Life-Cycle Events

Within each stage of the life cycle of a page, the page raises events that you can handle to run your own code. For control events, you bind the event handler to the event, either declaratively using attributes such as onclick, or in code.

Pages also support automatic event wire-up, meaning that ASP.NET looks for methods with particular names and automatically runs those methods when certain events are raised. If the AutoEventWireup attribute of the @ Page directive is set to true, page events are automatically bound to methods that use the naming convention of Page_event, such as Page_Load and Page_Init. For more information on automatic event wire-up, see ASP.NET Web Server Control Event Model.

The following table lists the page life-cycle events that you will use most frequently. There are more events than those listed; however, they are not used for most page-processing scenarios. Instead, they are primarily used by server controls on the ASP.NET Web page to initialize and render themselves. If you want to write custom ASP.NET server controls, you need to understand more about these events. For information about creating custom controls, see Developing Custom ASP.NET Server Controls.

Page Event	Typical Use
PreInit	Raised after the start stage is complete and before the initialization stage begins. Use this event for the following: Check the IsPostBack property to determine whether this is the first time the page is being processed. The IsCallback and IsCrossPagePostBack properties have also been set at this time. 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.
Init	Raised after all controls have been initialized and any skin settings have been applied. The Init event of individual controls occurs before the Init event of the page. Use this event to read or initialize control properties.
InitComplete	Raised at the end of the page's initialization stage. Only one operation takes place between the Init and InitComplete events: tracking of view state changes is turned on. View state tracking enables controls to persist any values that are programmatically added to the ViewState collection. Until view state tracking is turned on, any values added to view state are lost across postbacks. Controls typically turn on view state tracking immediately after they raise their Init event. Use this event to make changes to view state that you want to make sure are persisted after the next postback.
PreLoad	Raised after the page loads view state for itself and all controls, and after it processes postback data that is included with the Request instance.
Load	The Page object calls the OnLoad method on the Page object, and then recursively does the same for each child control until the page and all controls are loaded. The Load event of individual controls occurs after the Load event of the page. Use the OnLoad event method to set properties in controls and to establish database connections.
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.
LoadComplete	Raised at the end of the event-handling stage. Use this event for tasks that require that all other controls on the page be loaded.
PreRender	Raised after the Page object has created all controls that are required in order to render the page, including child controls of composite controls. (To do this, the Page object calls EnsureChildControls for each control and for the page.) The Page object raises the PreRender event on the Page object, and then recursively does the same for each child control. The PreRender event of individual controls occurs after the PreRender event of the page. Use the event to make final changes to the contents of the page or its controls before the rendering stage begins.
PreRenderComplete	Raised after each data bound control whose DataSourceID property is set calls its DataBind method. For more information, see Data Binding Events for Data-Bound Controls later in this topic.
SaveStateComplete	Raised after view state and control state have been saved for the page and for all controls. Any changes to the page or controls at this point affect rendering, but the changes will not be retrieved on the next postback.
Render	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 a Render method that writes out the control's markup to send 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. For more information, see Developing Custom ASP.NET Server Controls. A user control (an .ascx file) automatically incorporates rendering, so you do not need to explicitly render the control in code.
Unload	Raised 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.

Additional Page Life Cycle Considerations

Individual ASP.NET server controls have their own life cycle that is similar to the page life cycle. For example, a control's Init and Load events occur during the corresponding page events.

Although both Init and Load recursively occur on each control, they happen in reverse order. The Init event (and also the Unload event) for each child control occur before the corresponding event is raised for its container (bottom-up). However the Load event for a container occurs before the Load events for its child controls (top-down). Master pages behave like child controls on a page: the master page Init event occurs before the page Init and Load events, and the master page Load event occurs after the page Init and Load events.

When you create a class that inherits from the Page class, in addition to handling events raised by the page, you can override methods from the page's base class. For example, you can override the page's InitializeCulture method to dynamically set culture information. Note that when an event handler is created using the Page_event syntax, the base implementation is implicitly called and therefore you do not need to call it in your method. For example, the base page class's OnLoad method is always called, whether you create a Page_Load method or not. However, if you override the page OnLoad method with the override keyword (Overrides in Visual Basic), you must explicitly call the base method. For example, if you override the OnLoad method on the page, you must call base.Load (MyBase.Load in Visual Basic) in order for the base implementation to be run.

The following illustration shows some of the most important methods of the Page class that you can override in order to add code that executes at specific points in the page life cycle. (For a complete list of page methods and events, see the Page class.) The illustration also shows how these methods relate to page events and to control events. The sequence of methods and events in the illustration is from top to bottom, and within each row from left to right.

Catch-Up Events for Added Controls

If controls are created dynamically at run time or declaratively within templates of data-bound controls, their events are initially not synchronized with those of other controls on the page. For example, for a control that is added at run time, the Init and Load events might occur much later in the page life cycle than the same events for controls created declaratively. Therefore, from the time that they are instantiated, dynamically added controls and controls in templates raise their events one after the other until they have caught up to the event during which it was added to the Controls collection.

Data Binding Events for Data-Bound Controls

To help you understand the relationship between the page life cycle and data binding events, the following table lists data-related events in data-bound controls such as the GridView, DetailsView, and FormView controls.

Nested Data-Bound Controls

If a child control has been data bound, but its container control has not yet been data bound, the data in the child control and the data in its container control can be out of sync. This is true particularly if the data in the child control performs processing based on a data-bound value in the container control.

For example, suppose you have a GridView control that displays a company record in each row, and it displays a list of the company officers in a ListBox control. To fill the list of officers, you would bind the ListBox control to a data source control (such as SqlDataSource) that retrieves the company officer data using the company ID in a query.

If the ListBox control's data-binding properties, such as DataSourceID and DataMember, are set declaratively, the ListBox control will try to bind to its data source during the containing row's DataBinding event. However, the CompanyID field of the row does not contain a value until the GridView control's RowDataBound event occurs. In this case, the child control (the ListBox control) is bound before the containing control (the GridView control) is bound, so their data-binding stages are out of sync.

To avoid this condition, put the data source control for the ListBox control in the same template item as the ListBox control itself, and do not set the data binding properties of the ListBox declaratively. Instead, set them programmatically at run time during the RowDataBound event, so that the ListBox control does not bind to its data until the CompanyID information is available.

For more information, see Binding to Data Using a Data Source Control.

Login Control Events

The Login control can use settings in the Web.config file to manage membership authentication automatically. However, if your application requires you to customize how the control works, or if you want to understand how Login control events relate to the page life cycle, you can use the events listed in the followinbg table.

Application Designing-Requirements to Prototypes

Application design is one of the most critical part of software design..it it’s right the road ahead is a cakewalk…if not…Nightmare begins.

Here I am starting a series of posts that will explore the application design processes and tools in detail.

 Prior to application design, Requirement gathering constitutes the basic framework on which design is built. The requirements need to be analyzed from 4 perspectives to make valid requirements docs. The figure below sums up these perspectives

Here QoS is Quality of Service that also needs to be considered.

Use cases also are a means of defining the requirements and sometimes serve as the main basis for application design; however there are some basic differences.

Use Cases versus Requirements
    A use case is a Unified Modeling Language (UML) model meant to describe a set of user steps that accomplish a task.
Requirements define what must be created to satisfy the needs of the user. Together, they provide a good view of how the user sees the system.
One the requirements are finalized, the Prototype validates the requirements that can be a POC or Mockups.

Mockups and Proof-of-Concept Prototypes
    A mockup is meant to verify the requirements and use cases through the creation of a number of key screens in the system. Mockups are also called horizontal prototypes because they take a single, horizontal picture of the application. They do not go deeply (or vertically) into the other layers of the application such as the business objects and the database layers. Mockups are a great way to determine whether the requirements are complete and understood. They also help validate the use cases, the navigational structure, and some of the logical interactions of the application.

Mockups shortcomings
    They do not help to prove any of the architecture concepts for the system. They also do not validate the technology decisions.

Mockups Advantages:
    Mockups are useful for defining how the application will look and behave. This removes ambiguity from the implementation and builds early consensus on what will be delivered.

A proof-of-concept prototype is meant to validate the requirements and confirm the technology recommendations and high-level design. A proof-of-concept prototype is also called a vertical prototypebecause it looks at the application across the entire stack (UI, services, business objects, and database). Proof-of-concept prototypes have also been called reference architectures because they provide a reference for the development team on just how the system should work from top to bottom. This removes ambiguity, creates a standard, and eliminates a lot of risk.

Proof-of-concept prototype is generally, created by choosing a key requirement of the application and then building it out through each layer of the design. It makes more sense to prove out a riskier requirement than to work with a well-known requirement.

After going through the above exercises, the main work of design begins, as summarized below.

 

As the above figure depicts the first design phase is to develop Logical Model. All these designing phases make use of certain diagramming techniques ranging from ORM diagrams to Sequence and collaboration Diagrams.

These Diagrams will be covered in next post, which will explain all the used diagrams in detail.

Hope this was helpful..

Till Next we Connect….

Happy Learning.

One of the unique features of C# is the concept of Partial, extendable to definition of a Class or a Struct, an Interface or a method.
Using this, the definition of any class, struct, interface of method can exist in two or more source files. Each source file contains a section of the type or method definition, and all parts are combined when the application is compiled.

To split a class definition, partial keyword modifier is used.

For Example:

   1:      public partial class Pradeep

   2:      {

   3:          public void OnLeave()

   4:          {

   5:          }

   6:      }

   7:   

   8:      public partial class Pradeep

   9:      {

  10:          public void InMeeting()

  11:          {

  12:          }

  13:      }

Here, it is valid to use the same name for the class and implement desired functionality separately.
Finally, when compiled, the code is auto merged , giving a Final class named Pradeep, with the two methods that were defined separately.

The partial keyword indicates that other parts of the class, struct, or interface can be defined in the namespace.
Following are the points that need to be taken care of while working with Partial keyword.

• All the parts must use the partial keyword.

• All the parts must have the same accessibility, such as public, private, and so on.

• All partial-type definitions meant to be parts of the same type must be defined in the same assembly and the same module (.exe or .dll file). Partial definitions cannot span multiple modules.

• If any part is declared abstract, then the whole type is considered abstract.

• If any part is declared sealed, then the whole type is considered sealed.

• If any part declares a base type, then the whole type inherits that class.

• Parts can specify different base interfaces, and the final type implements all the interfaces listed by all the partial declarations.

• Nested types can be partial, even if the type they are nested within is not partial itself

For Example:

    class LeaveReachTimings
    {
        partial class Residence
        {
            void TimetoReach() { }
        }
        partial class Office
        {
            void TimeToLeave() { }
        }
    }

Here the Class LeaveReachTimings is not partial, but it is completely valid to declare partial classes Residence and Office as nested classes in it.

• Attributes of partial-type definitions are merged

For Example

    [SerializableAttribute]
    partial class CurrentCompany { }

    [Obsolete Attribute]
    partial class CurrentCompany { }

    These two attributes will finally merge and are equivalent to the following.

    [SerializableAttribute]
    [Obsolete Attribute]
    partial class CurrentCompany { }

Enough of Theory Let us now create one partial Class to verify the concepts covered so far.

    public partial class Record
    {
        private int x;
        private int y;

        public Record(int x, int y)
        {
            this.x = x;
            this.y = y;
        }
    }

    public partial class Record
    {
        public int PrintSum()
        {
            return x + y;
        }

    }

Similar to Partial Classes, Partial Methods are also allowed. These are allowed in partial classes or struct.
One part of class contains the signature and the same or other part of the partial class can contain its implementation.
If no implementation is provided, then the method and all calls made to it are removed at compile time.

Therefore, any code in the partial class can use a partial method, even if the implementation is not supplied. No compile-time or run-time errors will result if the method is called but not implemented.

A partial method declaration consists of two parts: the definition, and the implementation. These may be in separate parts of a partial class, or in the same part.

If there is no implementation declaration, then the compiler optimizes away both the defining declaration and all calls to the method.

Following are the considerations with Partial Methods.

• Partial method declarations must begin with the partial keyword

• Return Type is always void.

• out parameters are not allowed , however ref can be used.

• Partial methods cannot be virtual as they are implicitly private.

It means they have access modifiers such as public, private or internal. Hence, they cannot be called from outside the partial class, and cannot be declared as virtual.

• Partial methods cannot be extern, because the presence of the body determines whether they are defining or implementing.

• Partial methods can use static and unsafe modifiers.

• Partial methods can be generic.

• A delegate to a partial method which has an implementation, can be made. But, the partial method which has just a signature and no implementation can not have a delegate.

Example:

    public partial class PartialClassTest
    {
        private string mytest = string.Empty;

        partial void MyPartialMethodTest();

    }


    public partial class PartialClassTest
    {
        partial void MyPartialMethodTest()
        {
            mytest = "Partial Method call Succeded!!";

        }

        public string returnstring()
        {
            MyPartialMethodTest();
            return mytest;

        }
    }

Here the partial methods, always return void and to get the value of mytest string I have to declare yet another method(return string), which finally prints the string on the webpage if called as per the following code.

    protected void Page_Load(object sender, EventArgs e)
    {
        PartialClassTest ptest = new PartialClassTest();
        Response.Write(ptest.returnstring());
    }

Please note: Delegate or Enumeration declarations can not use partial keyword.

Hope this discussion was helpful.

Till Next time we connect, Happy Coding!!!