How Do I Make A Checkbox Checked By Default?-CodePudding

Using PHP and sessions, how can I check a checkbox the first time the page is loaded?

Here is a minimal sample of my code:

index.php:

<?php
session_start();
$_SESSION['foo'] = $_POST['foo'];
?>
<!doctype html>
<html>
  <body>
  <form method='POST'>
    <input type="checkbox" id="checkFoo" name="foo" <?php echo (isset($_POST['foo']) && $_POST['foo'] === 'on') ? 'checked' : ''; ?>>
    <label for="checkFoo">checkbox</label>
    <button type="submit">Submit</button>
  </form>
  <?php include 'print.php'; ?>
  </body>
</html>

print.php:

<?php
session_start();
echo $_SESSION['foo'].' ';
?>

Apart from the default value, this code works exactly as I intend:

When the user checks the checkbox and clicks submit, it prints 'on'
When the user unchecks the checkbox and clicks submit, it prints nothing
Clicking the submit button does not change the value of the checkbox

How can I change the default (startup) value of the checkbox to 'on', without changing the above behavior?

CodePudding user response：

When the page will be first loaded, the $_POST['submit'] would not be set as the page would be accessed using a GET Request.

So Modify the files: index.php

<?php
session_start();
$_SESSION['foo'] = $_POST['foo'] ?? '';
?>
<!doctype html>
<html>
  <body>
  <form method='POST'>
  <input type="checkbox" id="checkFoo" value="on" name="foo" <?php echo ((!isset($_POST['submit']) && $_SESSION['foo'] != 'off') || ($_SESSION['foo'] === 'on')) ? 'checked' : ''; ?>>

    <label for="checkFoo">checkbox</label>
    <button type="submit" name="submit">Submit</button>
  </form>
  <?php include 'print.php'; ?>
  </body>
</html>

print.php

<?php
if(!isset($_SESSION)) {
    session_start();
}
if(isset($_SESSION['foo'])) {
    echo $_SESSION['foo'].' ';
}
?>

CodePudding user response：

This is a little verbose, but it's good practice to use a default value, then check if something exists before setting a variable to it.

Something like this should work.

<?php
session_start();
// default value is on
$foo = "on";

// if session has a value, use it instead
if(isset($_SESSION["foo"])){
    $foo = $_SESSION["foo"];
}


// if post has a value, use it instead and set the session value
if(isset($_POST["foo"])){
    $foo = $_POST["foo"];
    $_SESSION["foo"] = $_POST["foo"];
}

$checked = $foo === "on";

This can be simplified in newer PHP versions (7 )

<?php
session_start();
$foo = $_POST["foo"] ?? $_SESSION["foo"] ?? "on";
$_SESSION["foo"] = $foo;