PHP登录表单刷新页面而不是重定向

<?php
session_start();
require("includes/connect.php");
?>

            <div class="container">
                <form class="form-signin" role="form" action="login.php" method="post">
                    <h2 class="form-signin-heading">Please sign in</h2>
                    <input type="text" class="form-control" placeholder="Username" name="username_login" required autofocus>
                    <input class="form-control" type="password"  placeholder="Password" name="user_password" required>
                    <button class="btn btn-lg btn-primary btn-block" type="submit">Sign in</button>
                    <label class="forgotten"><a href="forgottenpass.php">Forgotten password?</a></label>
                </form>
    <?php
    //if an admin or user session is already in progress then dont let them log in, redirect to 'index.php'
    if (isset($_SESSION['admin']) && ($_SESSION['admin'] == true) || isset($_SESSION['user']) && ($_SESSION['user'] == true)) {
        header ("Location: index.php");     
        //if use not logged in then
    }else{
        //if username and password are entered, blank before user fills form
        $usr = (isset($_POST['username_login'])? $_POST['username_login']:null);
        $pwd = (isset($_POST['user_password'])? $_POST['user_password']:null);
        $usr = mysqli_escape_string($conn, $usr); //Prevent against SQL Injection by avoiding "'" being executed
        $pwd = mysqli_escape_string($conn, $pwd); //Prevent against SQL Injection by avoiding "'" being executed
        if ($usr && $pwd){  
            $epwd = $pwd;
            $q = "SELECT * FROM users WHERE UName='$usr' LIMIT 1;";
            $resultset = mysqli_query($conn,$q);
            $rowcount = mysqli_num_rows($resultset);
            if ($rowcount==1){ 
                while ($userRow = mysqli_fetch_assoc($resultset)){
                    //Get the DB username and password to compare
                    $dataBaseEmail = $userRow['UName'];
                    $dataBasePass = $userRow['Password'];   
                    $userGroup = $userRow['UserLevelID'];
                }
            mysqli_free_result($resultset);
            unset($q);
            //Compare DB user and pass to those entered
            if ($usr == $dataBaseEmail && $epwd == $dataBasePass){
                //Now that we know they are activated ect, we can create a session based on their privlidges 
                if ($userGroup ==1){ //ADMIN load the console 
                    header("Location: index.php");
                    $_SESSION['admin'] = true;
                }else{ //Normal User
                    header ("Location: logout.php");
                    $_SESSION['user'] = true;
                    $_SESSION['user'] = $dataBaseEmail;
                    }  
                }else{//user and pass do not match DB
                    echo '<div class="login-error">Incorrect Password, try again</div>';     
                }
            }else{
                echo '<div class="login-error">Error: There is no such user registered on the system. Please check the username and password entered.</div>';
            }
        }
    }
    ?>
            </div> <!-- /container -->

头语句必须在任何HTML代码之前使用。来源:http://pl1.php.net/manual/en/function.header.php

再次检查您的代码，您的查询在admin会话检查后继续破坏，因为您没有添加如果表单张贴检查

在这行

if (isset($_SESSION['admin']) && ($_SESSION['admin'] == true) || isset($_SESSION['user']) && ($_SESSION['user'] == true)) {
    header ("Location: index.php");     
    //if use not logged in then
}else{

在else后添加另一个if语句

if (isset($_SESSION['admin']) && ($_SESSION['admin'] == true) || isset($_SESSION['user']) && ($_SESSION['user'] == true)) {
    header ("Location: index.php");     
    //if use not logged in then
 }else
    if ( trim($_POST['username_login']) AND trim($_POST['user_password']))
    {

您必须将LOGIN code的位置更改为before HTML tags，因为header()在header发送任何输出到客户端浏览器后将不起作用。

<?php
session_start ();
require ("includes/connect.php");
            //Check for FORM POST 
            if (isset ( $_POST ['username_login'] ) && isset ( $_POST ['user_password'] )) {
                // if an admin or user session is already in progress then dont let them log in, redirect to 'index.php'
                if (isset ( $_SESSION ['admin'] ) && ($_SESSION ['admin'] == true) || isset ( $_SESSION ['user'] ) && ($_SESSION ['user'] == true)) {
                    header ( "Location: index.php" );
                    // if use not logged in then
                } else {
                    // if username and password are entered, blank before user fills form
                    $usr = (isset ( $_POST ['username_login'] ) ? $_POST ['username_login'] : null);
                    $pwd = (isset ( $_POST ['user_password'] ) ? $_POST ['user_password'] : null);
                    $usr = mysqli_escape_string ( $conn, $usr ); // Prevent against SQL Injection by avoiding "'" being executed
                    $pwd = mysqli_escape_string ( $conn, $pwd ); // Prevent against SQL Injection by avoiding "'" being executed
                    if ($usr && $pwd) {
                        $epwd = $pwd;
                        $q = "SELECT * FROM users WHERE UName='$usr' LIMIT 1;";
                        $resultset = mysqli_query ( $conn, $q );
                        $rowcount = mysqli_num_rows ( $resultset );
                        if ($rowcount == 1) {
                            while ( $userRow = mysqli_fetch_assoc ( $resultset ) ) {
                                // Get the DB username and password to compare
                                $dataBaseEmail = $userRow ['UName'];
                                $dataBasePass = $userRow ['Password'];
                                $userGroup = $userRow ['UserLevelID'];
                            }
                            mysqli_free_result ( $resultset );
                            unset ( $q );
                            // Compare DB user and pass to those entered
                            if ($usr == $dataBaseEmail && $epwd == $dataBasePass) {
                                // Now that we know they are activated ect, we can create a session based on their privlidges
                                if ($userGroup == 1) { // ADMIN load the console
                                    header ( "Location: index.php" );
                                    $_SESSION ['admin'] = true;
                                } else { // Normal User
                                    header ( "Location: logout.php" );
                                    $_SESSION ['user'] = true;
                                    $_SESSION ['user'] = $dataBaseEmail;
                                }
                            } else { // user and pass do not match DB
                                echo '<div class="login-error">Incorrect Password, try again</div>';
                            }
                        } else {
                            echo '<div class="login-error">Error: There is no such user registered on the system. Please check the username and password entered.</div>';
                        }
                    }
                }
            }
            ?>
<!-- container -->
<div class="container">
<form class="form-signin" role="form" action="login.php" method="post">
    <h2 class="form-signin-heading">Please sign in</h2>
    <input type="text" class="form-control" placeholder="Username"
        name="username_login" required autofocus> 
        <input class="form-control" type="password" placeholder="Password" name="user_password" required>
        <button class="btn btn-lg btn-primary btn-block" type="submit">Sign in</button>
    <label class="forgotten">
            <a href="forgottenpass.php">Forgotten password?</a></label>
</form>
</div>
<!-- /container -->

".mysql_errno();｝｝其他的{回声mysql_error()。
".mysql_errno ();｝//echo $用户名。"——"美元密码;?>

<form class="form-signin" role="form" action="login.php" method="post">
                <h2 class="form-signin-heading">Please sign in</h2>
                <input type="text" class="form-control"  placeholder = "Username"name="username_login" >
                <input class="form-control" type="password" placeholder = "password"  name="user_password" >
                <button class="btn btn-lg btn-primary btn-block" type="submit">Sign in</button>
                <label class="forgotten"><a href="../forgottenpass.php">Forgotten password?</a></label>
   </form>