ITEC 325 2014spring ibarland

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lect09-forms
html input forms, and php
chapter 3

From PHP Visual Quickstart Guide by Larry Ullman
Originally based on notes by Jack Davis (jcdavis@radford.edu)

• HTML tags for Input Fields
  • check boxes

    <input type='checkbox' name='cb1' value='milk' id='cbOne' checked='checked' />

  • text fields,

    <input type='text' name='txt1' size='10' maxlength='8' id='txtone' />

  • radio buttons

    <input type='radio' name='age' value='over50' /> <br/> <input type='radio' name='age' value='30to50' /> <br/> <input type='radio' name='age' value='under30' /> <br/>

    
    
    
    
    The variable "age" will be set to one of the three values.
    (A second set of unrelated radio buttons would share a different name attribute.)
    
  • textareas:

    <textarea name='comments' rows='3' cols='30'> Initial Contents </textarea>

    Initial Contents
    Note that this isn't an input tag — text areas get their own tag type, “textarea”.

    (I'm not really sure why text areas are different from from checkboxes/radio-buttons/text-fields¹. It'd seem more sensible to either have a single tag input with attributes for every possible type of input-widget, or have each type of input-widget be its own stand-alone tag. But going half-and-half on the issue only confuses me.)

  • Select Boxes (drop-down)

    <select name='title'> <option value = 'mr'>Mr.</option> <option value = 'ms'>Ms.</option> <option value = 'mrs'>Mrs.</option> <option value = 'miss'>Miss</option> </select>

    Mr. Ms. Mrs. Miss
  • Submit button:

    <input type='submit' value='Submit Data to Server' />

  • Reset button:

    <input type='reset' value='Clear Form' />

• Form Example
  • Simple Form Example
    lect09-forms.php
• Remember: <input name='aNodeName' /> uses the name attribute to pass information in the action/request, but <label for='aNodeId'>… uses id to refer to the DOM node of the current tree. (It makes good sense, but takes a moment of thought.)
• GET & POST methods

  Q: But how is information communicated from a web form (pure html) to a php program?
  A: When you click 'submit', the HTML makes a page-request to the page specified by the form's "action" attribute. (Presumably it's a php page.) The page-request incudes extra information about what html input fields had been selected, etc., as part of the http request. The server gets that request and invokes the php file as normal, but it also pre-initializes an array of values for the program — and it fills that array with the extra information contained in the page-request.

  • GET - form data is sent to the server appended to the server script URL
    In the server script, data is retrieved via the super global associative array $_GET.
  • POST - form data is embedded in the http request header
    Server script - $_POST
  When to use which?:
  • GET requests can be bookmarked;
  • GET requests should be idempotent — that is, fetching the same request twice should be the same as getting it once. Even better, they should have no side-effects²³.
    So if your form causes a bank transfer to happen, or adds something to the user's shopping-cart, or updates a database, then GET is probably not appropriate.
  • POST requests are more secure against casual looking over the shoulder (but still vulnerable to packet sniffing etc.)
  • When refreshing a page created via POST, browsers tend to respond: “Refreshing will cause the page to re-submit; do you really want to do this?”
  • Possible guideline (?): If the page is changing a database's contents, use POST.
  • Many people suggest using POST as default.
  • Explore: How does a newspaper handle it? nytimes. Discuss: When might you choose to use post/get vs. could just have a separate URL for each result, e.g. different xkcd strips.

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©2014, Ian Barland, Radford University Last modified 2014.Feb.10 (Mon)

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