4.2 MVC Application Architecture

• List the three components.

• Any good idea to send data without displaying to the user or obtaining from the user?
• There is one input type for this purpose. What is it?
  'hidden'

  <form action='controller.php' method='POST'> <-- in view_startpage.php -->
      <input type='hidden' name='page' value='StartPage'>
      <input type='hidden' name='command' value='SignIn'>
      <input type='text' name='username'>
      <input type='password' name='password'>
      <input type='submit'>
  </form>
  

• Here is an example of controller.php with the above <form>.

  <?php
  //---- Case 1 ----
  if (empty($_POST['page']) {  // What does this mean?
      include("view_startpage.php");  // Logically the code in "view_..." will be copied to this position.
      exit();
  } 
  
  //---- Case 2 ----
  $page = $_POST['page'];
  if ($page == 'StartPage') {
      $command = $_POST['command'];  // In view_startpage.php, an input in a form, of which type is 'hidden' and name is 'command'.
      switch($command) {
          case 'SignIn':
              ...
              exit();  // or break when there is something more to do after switch
          case 'Join':  // or 'SignUp;
              ...
              exit();
          case 'ForgotPassword':
              ...
              exit();
          default:
              ...
              exit();
      }
  }
  
  //---- Case 3 ----
  else if ($page == 'MainPage') {
      ...
      exit();
  }
  
  //---- Case 4 ----
  else {
      ...
      exit();
  }
  ?>
  

• Trial 0.5: Assuming the GET method, let's check if the 'page' value is empty. If so, include "e5_view_startpage.php" and exit. Note that "e5_view_startpage.php" includes the client-side code.
  <?php if (????) { ???("e5_view_startpage.php"); // Logically the code in "e5_..." will be copied to this position. ???; } ?> Submit the code to the server to execute PHP code
  
• Trial 1: Let's try to route the command sent from the client.
  <?php /* Just for testing; Let's assume the data were sent from the client to controller.php. */ $_POST['page'] = 'StartPage'; // In view_startpage.php, an input in a form, of which type is 'hidden' and name is 'StartPage'. $_POST['command'] = ???; // SignIn $_POST['username'] = 'John'; $_POST['password'] = 'topsecretpassword'; ?> <?php // In controller.php, $page = $_POST[???]; if (????) { // If the data came from StartPage $command = $_POST[???]; ???($command) { ???? // SignIn case echo 'Username = ' . ??? . ', Password = ' ??? ??? . '<br>'; if (is_valid(???, ???)) // is_valid() is defined below for testing. echo 'Valid username and password<br>'; ??? echo 'Invalid username and password<br>'; exit(); // or break when there is something more to do after switch case 'Join': // or 'SignUp' //... ???(); case 'ForgotPassword': //... exit(); ???: echo 'Unknown command<br>'; exit(); } } // Just for testing here. It will be moved to Model. ??? is_valid($u, $p) { ???; // return if $u is 'comp3540' and $p is 'topsecretpassword'. Otherwise, false } ?> Submit the code to the server to execute PHP code
  
• What if there are a lot of things to do for each command, such as accessing DB and generating new client side code?
• Another question is how to use Controller with Model and View? How to logically separate Controller, Model, and View?

• include() and require() are like the import statement in Java and the include statement in C.
• How are include() and require() different?
• When AA.php includes or requires BB.php, all the code in BB.php will be logically copied into AA.php and the PHP code will be executed.
• Can all the variables in AA.php, that are declared before the inclusion of BB.php, be used with the code in BB.php?
  YES
• When AA.php includes or requires BB.php, can all the variables in BB.php be used in AA.php after the inclusion?
  YES
• The two questions in the above are very important when you use MVC with PHP. This is how Controller sends information to View/Model and how View/Model sends information to Controller.

• <!-- controller.php -->
  <?php
  ...
  $display_modal_window = 'signin';
  include ('view_startpage.php');  // When controller.php is executed,
                                   // this will be replaced by the code in 'view_startpage.php'.
  ...
  ?>
  ---------------------------------------
  <!-- view_startpage.php -->
  ...
  window.addEventListener('load', function() {
      ...;
      <?php
          if ($display_modal_window == 'signin')
              echo 'show_signin();'; // send JavaScript code back to the client
      ?>
  });
  ...
  

• The 'include' statement in the above controller will include the view_startpage.php in the controller and the included code is executed. In this example, logically speaking, $display_modal_window is used to pass information to the code in vew_startpage.php. After the inclusion, controller.php becomes like

  <!-- controller.php -->
  <?
  ...
  $display_modal_window = 'signin';
  ?>
      ...
      window.addEventListener('load', function() {
          ...;
          <?php
              if ($display_modal_window == 'signin')
                  echo 'show_signin();';  // echo JavaScript code
          ?>
      });
      ...
  <?php
  ...
  ?>
  

• What HTML/CSS/JS content will be sent to the client after the above PHP code in controller.php is executed with $display_modal_window = 'signin'?

  ...
  window.addEventListener('load', function() {
    ...;
    show_signin();
    ...
  });
  ...
  

• Start web page - initially no SignIn box; accepts commands, such as SignIn (or Login), Join (or SignUp), ForgotPassword, ..., and submits them to the controller
• Main web page - accepts some other commands, such as SignOut, Search, ..., and submits them to the controller

• Case 1: controller.php is directly accessed. Not from StartPage nor MainPage.
• Case 2: Or some commands come from StartPage.
• Case 3: Or some other commands come from MainPage.
• How many different types of values must be submitted to controller.php?

<?php
// Case 1: When no page value is sent from the client
if (empty($_POST['page'])) {  // That is, controller.php is the URL of TRUQA. http://cs.tru.ca/.../controller.php
                              // No POST or GET data comes.
                              // You may use if (!isset($_POST['page'])) instead of empty(...).
    $display_modal_window = 'none';  // This variable will be used in 'view_startpage.php'.
                              // It will display the start page without any modal window, i.e., no SignIn box, no Join box, ...
    include ('view_startpage.php');  // The user will see StartPage without any modal window on.
    exit();
}

require('model.php');  // This file includes some routines to access DB.
...

// Case 2: When a command comes from StartPage
if ($_POST['page'] == 'StartPage')
{
    $command = $_POST['command'];
    switch($command) {  // When a command is sent from the client through the SignIn modal window
        case 'SignIn':  // With username and password
            if (there is an error in username and password) {
                $error_msg_username = '* Wrong username, or';
                $error_msg_password = '* Wrong password'; // Set an error message into a variable.
                                                          // This variable will used in the form in 'view_startpage.php'.
                $display_modal_window = 'signin';  // It will display the start page with the SignIn box.
                                                   // This variable will be used in 'view_startpage.php'.
                include('view_startpage.php');  // The user will see StartPage with the SignIn modal window on.
            } else
                include ('view_mainpage.php');  // The user will see MainPage.
            exit();
        case 'Join':  // or 'SignUp' with username, password, email, some other information
            ...
            exit();
        ...
    }
}

// Case 3: When a command comes from 'MainPage'
else if ($_POST['page'] == 'MainPage'){
    ...
}
?>