05 html-forms

05 html-forms

• 1.
  HTML/XHTML Forms Aug 24, 2012
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  What are forms?  <form> is just another kind of XHTML/HTML tag  Forms are used to create (rather primitive) GUIs on Web pages  Usually the purpose is to ask the user for information  The information is then sent back to the server  A form is an area that can contain form elements  The syntax is: <form parameters> ...form elements... </form>  Form elements include: buttons, checkboxes, text fields, radio buttons, drop-down menus, etc  Other kinds of tags can be mixed in with the form elements  A form usually contains a Submit button to send the information in he form elements to the server  The form’s parameters tell JavaScript how to send the information to the server (there are two different ways it could be sent)  Forms can be used for other things, such as a GUI for simple programs 2
• 3.
  Forms and JavaScript  The JavaScript language can be used to make pages that “do something”  You can use JavaScript to write complete programs, but...  Usually you just use snippets of JavaScript here and there throughout your Web page  JavaScript code snippets can be attached to various form elements  For example, you might want to check that a zipcode field contains a 5-digit integer before you send that information to the server  Microsoft calls its version of JavaScript “active scripting”  Forms can be used without JavaScript, and JavaScript can be used without forms, but they work well together  JavaScript for forms is covered in a separate lecture 3
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  The <form> tag  The <form arguments> ... </form> tag encloses form elements (and probably other elements as well)  The arguments to form tell what to do with the user input  action="url" (required)  Specifies where to send the data when the Submit button is clicked  method="get" (default)  Form data is sent as a URL with ?form_data info appended to the end  Can be used only if data is all ASCII and not more than 100 characters  method="post"  Form data is sent in the body of the URL request  Cannot be bookmarked by most browsers  target="target"  Tells where to open the page sent as a result of the request  target= _blank means open in a new window  target= _top means use the same window 4
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  The <input> tag  Most, but not all, form elements use the input tag, with a type="..." argument to tell which kind of element it is  type can be text, checkbox, radio, password, hidden, submit, reset, button, file, or image  Other common input tag arguments include:  name: the name of the element  id: a unique identifier for the element  value: the “value” of the element; used in different ways for different values of type  readonly: the value cannot be changed  disabled: the user can’t do anything with this element  Other arguments are defined for the input tag but have meaning only for certain values of type 5
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  Text input A textfield: <input type="text" name="textfield" value="with an initial value" /> A multi-line text field <textarea name="textarea" cols="24" rows="2">Hello</textarea> A password field: <input type="password" name="textfield3" value="secret" /> • Note that two of these use the input tag, but one uses textarea 6
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  Buttons  A submit button: <input type="submit" name="Submit" value="Submit" />  A reset button: <input type="reset" name="Submit2" value="Reset" />  A plain button: <input type="button" name="Submit3" value="Push Me" />  submit: send data  reset: restore all form elements to their initial state  button: take some action as • Note that the type is input,specified by JavaScript not “button” 7
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  Radio buttons Radio buttons:<br> <input type="radio" name="radiobutton" value="myValue1" /> male<br> <input type="radio" name="radiobutton" value="myValue2” checked="checked" />female  If two or more radio buttons have the same name, the user can only select one of them at a time  This is how you make a radio button “group”  If you ask for the value of that name, you will get the value specified for the selected radio button  As with checkboxes, radio buttons do not contain any text 8
• 9.
  Labels  In many cases, the labels for controls are not part of the control  <input type="radio" name="gender" value="m" />male  In this case, clicking on the word “male” has no effect  A label tag will bind the text to the control  <label><input type="radio" name="gender" value="m" />male</label>  Clicking on the word “male” now clicks the radio button  w3schools says that you should use the for attribute:  <label for="lname">Last Name:</label> <input type="text" name="lastname" id="lname" />  In my testing (Firefox and Opera), this isn’t necessary, but it may be for some browsers  Labels also help page readers read the page correctly  Some browsers may render labels differently 9
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  Checkboxes  A checkbox: <input type="checkbox" name="checkbox" value="checkbox" checked="checked">  type: "checkbox"  name: used to reference this form element from JavaScript  value: value to be returned when element is checked  Note that there is no text associated with the checkbox  Unless you use a label tag, only clicking on the box itself has any effect 10
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  Drop-down menu orlist  A menu or list: <select name="select"> <option value="red">red</option> <option value="green">green</option> <option value="BLUE">blue</option> </select>  Additional arguments:  size: the number of items visible in the list (default is "1")  multiple  if set to "true" (or just about anything else), any number of items may be selected  if omitted, only one item may be selected  if set to "false", behavior depends on the particular browser 11
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  Hidden fields  <input type="hidden" name="hiddenField" value="nyah"> &lt;-- right there, don't you see it?  What good is this?  All input fields are sent back to the server, including hidden fields  This is a way to include information that the user doesn’t need to see (or that you don’t want her to see)  The value of a hidden field can be set programmatically (by JavaScript) before the form is submitted 12
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  A complete example <html> <head> <title>GetIdentity</title> <meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1"> </head> <body> <p><b>Who are you?</b></p> <form method="post" action=""> <p>Name: <input type="text" name="textfield"> </p> <p>Gender: <label><input type="radio" name="gender" value="m" />Male<label> <label><input type="radio" name="gender" value="f" />Female</label> </p> </form> </body> </html> 13
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  The End 14