如何使用下拉框创建一个for循环

Question

Hi I am trying to create a set of drop down boxes that will use an array of data from the values that you pick and then runs through a loop to post them to the screen at the moment the data that i want to use will just be local but i want to edit this later so that it will loop through the data from my database and post that to the screen. i have looked at other questions on this subject and just wondering how i would change it for my code i have looked at this link questions on stack overflow that I have looked at i have just got a couple questions that im wondering if anybody has seen this before or if they have seen any examples i have also looked at for loops and i understand the concept

my questions to you are:

1) how would I post the values from my drop down boxes into a php array 2) how would I then check the values against and array of data and then choose which are correct and post them to the screen. 3)Would I need to use a second language like javascript or can it be done just in php

My drop down box code is

<div id="Content">

    <?php include "select.class.php"; ?>
    <form id="select_form">
        Choose a category:<br />
        <select id="category">
            <?php echo $opt->ShowCategory(); ?>
        </select>
        <br /><br />

        Choose a type:<br />
        <select id="type">
            <option value="%">any...</option>
        </select>
        <br /><br />

        Choose a principle:<br />
        <select id="principle">
            <option value="%">any...</option>
        </select>
        <br /><br />

        <input type="submit" value="confirm" />
    </form>
    <div id="result"></div>

    <!-- end of the Options -->

below is the select.class.php

<?php
    class SelectList
    {
        protected $conn;

            public function __construct()
            {
                $this->DbConnect();
            }

            protected function DbConnect()
            {
                include "db_config.php";
                $this->conn = mysql_connect($host,$user,$password) OR die("Unable to connect to the database");
                mysql_select_db($db,$this->conn) OR die("can not select the database $db");
                return TRUE;
            }

            public function ShowCategory()
            {
                $sql = "SELECT * FROM subject";
                $res = mysql_query($sql,$this->conn);
                $category = '<option value="0">choose...</option>';
                while($row = mysql_fetch_array($res))
                {
                    $category .= '<option value="' . $row['subject_id'] . '">' . $row['description'] . '</option>';
                }
                return $category;
            }

            public function ShowType()
            {
                $sql = "SELECT * FROM section WHERE subject_id=$_POST[id]";
                $res = mysql_query($sql,$this->conn);
                $type = '<option value="0">choose...</option>';
                while($row = mysql_fetch_array($res))
                {
                    $type .= '<option value="' . $row['section_id'] . '">' . $row['description'] . '</option>';
                }
                return $type;
            }

             public function ShowPrinciple()
            {
                $sql = "SELECT * FROM principle WHERE section_id=$_POST[id]";
                $res = mysql_query($sql,$this->conn);
                $principle = '<option value="0">choose...</option>';
                while($row = mysql_fetch_array($res))
                {
                    $principle .= '<option value="' . $row['principle_id'] . '">' . $row['description'] . '</option>';
                }
                return $principle;
            }   
    }

    $opt = new SelectList();
?>

Answer 1

1) how would I post the values from my drop down boxes into a php array

In the form tag add method="POST". Reference in PHP with $_POST array. Make sure to validate and escape the data before writing to your DB.

2) how would I then check the values against and array of data and then choose which are correct and post them to the screen.

If you don't have millions of categories, you are better off sending them all as a JSON array and using Javascript. Something like:

<script>
var categories = <?php echo json_encode($opt->ShowCategory()); ?>;
</script>

json_encode may require some options to be set, depening on your character set. More info here: http://php.net/manual/en/function.json-encode.php

Making a new request each time someone changes a dropdown box will drive them crazy, I know I hate that. If you have used jQuery before, this is very easy. This isn't that difficult without it.

3)Would I need to use a second language like javascript or can it be done just in php

For the sake of your users, use Javascript.

Answer 2

code for showCategory()

...
$categories = new array();
$category = '<option value="0">choose...</option>';
while($row = mysql_fetch_array($res))
            {
                $categories[$row['subject_id']] = $row['description'];
            }
$validCategories = $this->getValidCategories() // get the valid categories 
foreach($categories as $index=>$cat){
   // only choose the categories that are valid
   if(array_search($cat,$validCategories) !== FALSE)
       $category.= '<option value="'.$index.'">'.$cat.'</option>'; 

}
return $category;