PHP没有从上一页的表单中获得任何响应

I have the file "1.php" and the file "2.php" ...

In "1.php", there's a HTML form:

<form action="2.php" method="post">
  <div class="form-group">
    <label for="db_username">Field 1:</label>
    <input type="text" class="form-control" id="db_username">
  </div>
  <div class="form-group">
    <label for="db_password">Field 2:</label>
    <input type="password" class="form-control" id="db_password">
  </div>
  <div class="form-group">
    <label for="db_passphrase">Field 3:</label>
    <input type="text" class="form-control" id="db_passphrase">
  </div>
  <button type="submit" class="btn btn-default">Next</button>
</form>

While in "2.php", the action must be applied in PHP .. like that:

<?php
// Process of Step "1"
$db_username = $_POST['db_username'];
$db_password = $_POST['db_password'];
$db_passphrase = $_POST['db_passphrase'];

if( !isset($db_username) || !isset($db_password) || !isset($db_passphrase) ) {
    header("Location: 1.php?error=1");
    die();
}
?>

However .. the values of $_POST['db_username'], $_POST['db_password'] and $_POST['db_passphrase'] is empty...

You need to use the name attribute to later access the $_POST data, as in:

<input type="text" class="form-control" id="db_username" name="db_username">

You need to give the inputs a name and acces that value through $_POST['name']. id is not relevant for php form handling

You have to give name for the textfields like this

<input type="text" class="form-control" id="db_username" name="db_username">

Put name instead of id. it should work