自定义验证消息不起作用 - Customized validation messages not working?

我试图将自定义验证消息添加到此表单中，但无法弄清楚我的一生。任何帮助/建议不胜感激...谢谢。

我已经尝试了一些教程，但似乎没有什么适合我，我确信它很简单，但我似乎无法弄清楚。

谢谢

验证表格：

<?php
if (isset($_POST['insert'])) {
  require_once('connection.php');
  $OK = false;
  $sql = 'INSERT INTO students (studentTitle, studentFirstName, studentLastName)
      VALUES(:studentTitle, :studentFirstName, :studentLastName)';
  $stmt = $conn->prepare($sql);
  $stmt->bindParam(':studentTitle', $_POST['studentTitle'], PDO::PARAM_STR);
  $stmt->bindParam(':studentFirstName', $_POST['studentFirstName'], PDO::PARAM_STR);
  $stmt->bindParam(':studentLastName', $_POST['studentLastName'], PDO::PARAM_STR);
  $stmt->execute();
  $OK = $stmt->rowCount();
  if ($OK) {
  header('Location: http://localhost/mysqlquiz/student.php');
  exit;
  } else {
  $error = $stmt->errorInfo();
  if (isset($error[2])) {
    $error = $error[2];
    }
  }
}
?>
<!DOCTYPE HTML>
<html>
<head>
<meta charset="utf-8">
<title>Add Student Details</title>
<link href="css/style.css" rel="stylesheet" type="text/css">
</head>
<body>
<h1 class="header">New student details</h1>
<p><a href="student.php">Student Listing </a></p>
<?php 
if (isset($error)) {
  echo "<p class='warning'>Error: $error</p>";
}
?>
    <?php
// define variables and set to empty values
$studentTitleErr = $studentFirstNameErr = $studentLastNameErr = "";
$studentTitle = $studentFirstName = $studentLastName = "";
if ($_SERVER["REQUEST_METHOD"] == "POST") {
   if (empty($_POST["studentTitle"])) {
     $studentTitleErr = "A title is required";
   } else {
     $studentTitle = test_input($_POST["studentTitle"]);
   }
   if (empty($_POST["studentFirstName"])) {
     $studentFirstNameErr = "First name is required";
   } else {
     $studentFirstName = test_input($_POST["studentFirstName"]);
   }
   if (empty($_POST["studentLastName"])) {
     $studentLastNameErr = "Last name is required";
   } else {
     $studentLastName = test_input($_POST["studentLastName"]);
   }
}
function test_input($data) {
   $data = trim($data);
   $data = stripslashes($data);
   $data = htmlspecialchars($data);
   return $data;
}
?>
    <form method="POST" action="<?php echo htmlspecialchars($_SERVER["PHP_SELF"]); ?>">
  <p>
      <label for="studentTitle">Title:</label>
      <select name="studentTitle" id="studentTitle" ><span class="error">* <?php echo $studentTitleErr;?></span>
            <option value="Mr">Mr.</option>
            <option value="Mrs">Mrs.</option>
            <option value="Ms">Ms.</option>
            <option value="Miss">Miss.</option>
     </select>
  </p>
  <p>
    <label for="studentFirstName">First Name:</label>
    <input type="text" name="studentFirstName" id="studentFirstName" ><span class="error">* <?php echo $studentFirstNameErr;?></span>
  </p>
  <p>
    <label for="studentLastName">Last Name:</label>
    <input type="text" name="studentLastName" id="studentLastName" ><span class="error">* <?php echo $studentLastNameErr;?></span>
  </p>
  <p>
    <input type="submit" name="insert" value="Add Details" id="insert">
    <input type="reset" name="clear" value="Clear" id="clear">
    <input name="studentID" type="hidden" value="<?php echo $studentID; ?>">
  </p>
</form>
</body>
</html>

我已经更新了你的代码。您应该先检查验证，然后插入。

<?php
// define variables and set to empty values
$studentTitleErr = $studentFirstNameErr = $studentLastNameErr = "";
$studentTitle = $studentFirstName = $studentLastName = "";
if (isset($_POST['insert'])) {
  require_once('connection.php');
  $error = $OK = false;
  if (empty($_POST["studentTitle"])) {
     $studentTitleErr = "A title is required";
$error = true;
   } else {
     $studentTitle = test_input($_POST["studentTitle"]);
   }
   if (empty($_POST["studentFirstName"])) {
     $studentFirstNameErr = "First name is required";
$error = true;
   } else {
     $studentFirstName = test_input($_POST["studentFirstName"]);
   }
   if (empty($_POST["studentLastName"])) {
     $studentLastNameErr = "Last name is required";
$error = true;
   } else {
     $studentLastName = test_input($_POST["studentLastName"]);
   }
if($error == false)
{
  $sql = 'INSERT INTO students (studentTitle, studentFirstName, studentLastName)
      VALUES(:studentTitle, :studentFirstName, :studentLastName)';
  $stmt = $conn->prepare($sql);
  $stmt->bindParam(':studentTitle', $_POST['studentTitle'], PDO::PARAM_STR);
  $stmt->bindParam(':studentFirstName', $_POST['studentFirstName'], PDO::PARAM_STR);
  $stmt->bindParam(':studentLastName', $_POST['studentLastName'], PDO::PARAM_STR);
  $stmt->execute();
  $OK = $stmt->rowCount();
  if ($OK) {
  header('Location: http://localhost/mysqlquiz/student.php');
  exit;
  } else {
  $error = $stmt->errorInfo();
  if (isset($error[2])) {
    $error = $error[2];
    }
  }
}
}
?>
<!DOCTYPE HTML>
<html>
<head>
<meta charset="utf-8">
<title>Add Student Details</title>
<link href="css/style.css" rel="stylesheet" type="text/css">
</head>
<body>
<h1 class="header">New student details</h1>
<p><a href="student.php">Student Listing </a></p>
<?php 
if (isset($error)) {
  echo "<p class='warning'>Error: $error</p>";
}
?>
    <?php
function test_input($data) {
   $data = trim($data);
   $data = stripslashes($data);
   $data = htmlspecialchars($data);
   return $data;
}
?>
    <form method="POST" action="<?php echo htmlspecialchars($_SERVER["PHP_SELF"]); ?>">
  <p>
      <label for="studentTitle">Title:</label>
      <select name="studentTitle" id="studentTitle" ><span class="error">* <?php echo $studentTitleErr;?></span>
            <option value="Mr">Mr.</option>
            <option value="Mrs">Mrs.</option>
            <option value="Ms">Ms.</option>
            <option value="Miss">Miss.</option>
     </select>
  </p>
  <p>
    <label for="studentFirstName">First Name:</label>
    <input type="text" name="studentFirstName" id="studentFirstName" ><span class="error">* <?php echo $studentFirstNameErr;?></span>
  </p>
  <p>
    <label for="studentLastName">Last Name:</label>
    <input type="text" name="studentLastName" id="studentLastName" ><span class="error">* <?php echo $studentLastNameErr;?></span>
  </p>
  <p>
    <input type="submit" name="insert" value="Add Details" id="insert">
    <input type="reset" name="clear" value="Clear" id="clear">
    <input name="studentID" type="hidden" value="<?php echo $studentID; ?>">
  </p>
</form>
</body>
</html>

因为您的数据库插入操作首先运行，并且没有检查所需的字段数据以运行或不运行。因此，它会运行，成功后它会重定向并退出：

header('Location: http://localhost/mysqlquiz/student.php');
exit;

这将清除POST并且所需的字段逻辑永远不会运行。