safaribook-essential-aspdotnot-web-forms-development/notes/1_WebApplicationDevelopment.md

# 1. Web Application Development

## 1.1 Introduction

Overview of this chapter:
* Client-server model.
* .NET Framework
* ASP.NET and C# Programming
* Visual Studio
* (Practice) How to start a new ASP.NET Web Application project

## 1.2 Client-Server Model

Client-Server Model distributes processing btw:
* **server**: provider of resources/services
  * e.g. of Web server app: *Internet Information Service (IIS)*, *Apache HTTP Server*, *Oracle iPlanet Web Server*
* **client**: users of resources
  * e.g. of Web client app: *Microsoft Internet Explorer*, *Google Chrome*.

### Web Page: Static or Dynamic

* Static web page: do not change for all requests.
  * Before HTML5, `.html/.htm` files are static web pages.
* Dynamic web page: 
  * 

![Processing cycle of a static Web page](imgs/493603_1_En_1_Fig2_HTML.jpg)
Processing cycle of a static Web page:
1. Client requests a Web page from a Web server via *HTTP request*. content of request: 
   1. Web page
   2. IP of server & client
2. After server received HTTP request, it 
   1. locates desired web page file. 
   2. Then attach HTML file to HTTP response.
   3. send back to client

![Processing cycle of a dynamic Web page](imgs/493603_1_En_1_Fig3_HTML.jpg)
Processing cycle of a dynamic Web page:
1. Client requests a Web page from a server via an HTTP request. content of request:
   1. name of dynamci Web page (e.g. `Display_Products.aspx`)
   2. state of Web page controls (e.g. name in text box)
2. After server received HTTP request
   1. Check file exentention is `.aspx`, then pass processing control to the business logic of the server app (i.e. ASP.NET & C# code)
   2. If business logic requies service from db (e.g. reading, inserting), the app server pass processing control and related args to db server.
   3. After db server finish execution, it pass control back to app server
   4. App server pass data/response back to web server
   5. Web server formats HTML based on app server's work
   6. Web server attach HTML to HTTP response
   7. Web server sends response back to client

This is a full backend service processing cycle

## 1.3 .NET Framework

* **.NET Framewok** = Windows-based software dev and execution framework
* It consists of 
  * **Framework Class Library (FCL)**: a large library of classes to create Windows desktop app, or Web app using VB, VC++, VC#, etc.
  * **Common Language Runtime (CLR)**: environment where all .NET app executed. (Execution logic shown below)

![Organization of the .NET Framework](imgs/493603_1_En_1_Fig4_HTML.jpg)

## 1.4 OOP

A class can contain *properties* & *methods* and can handle *events*.
* **event** = end-user actions or other things that occur in time.
* properties, methods, events are all **members** of the class

### 1.4.1 Class and Objects

2 types of classes in .NET Framework:
* **non-static class**: contain non-static members that we can use, ONLY after we initialize an object from it.
* **static class**: contain static members that can be directly utilized w/o initialization

Class diagram (e.g. shown below, used to describe class in the book) include:
* name of class
* **namespace** of the class resides in: contain classes that provide specific functionality or specialized tpe
* selected **properties**, **methods**, **events**
* **event handler methods** are omitted in diagram in this book
  * event handler methods = handler methods that raised by **event**; begin with "On", end with event name.

### 1.4.2 Properties

Properties:
* = data of class
* can be read from (via `get` method) and written to (via `set` method)

### 1.4.3 Methods

Omitted

### 1.4.4 Events

Events are things that happened
* Raised by user action or sth in future.
* When event is raised, methods are invoked to handle it.
  * e.g. .NET Page class raises a **Load** event every time client reload web page.
* Events can be static or non-static for different class.

#### 1.4.5 Encapsulation