Block submit after reload page - forms

Question

I "finished" my commenting system but one problem left.
After I write a comment and then reload the page, then the comment gets posted again..
Ive googled now 2~ hours and cant find some help
code:
<script type="text/javascript">
function toggle_comment(id) {
var e = document.getElementById(id);
if(e.style.display == 'block')
e.style.display = 'none';
else
e.style.display = 'block';
}
$(function() {
$(".submit").click(function() {
var comment = $("#comment").val();
var dataString = 'comment=' + comment;
if(comment=='')
{
alert('Please enter at least 30 characters');
return false
}
else
{
$.post("pages/comment.php", $("#postcommentform").serialize(), function(data) { });
}
});
});
$(function() {
$(".login").click(function() {
var username = $("#username").val();
var password = $("#password").val();
var dataString = 'username=' + username + '&password=' + password;
if(username=='' || password=='')
{
alert('Login is incorrect');
return false
}
else
{
$.post("pages/login.php", $("#postlogin").serialize(), function(data) { });
}
});
});
</SCRIPT>
<a class="sitelinksblue" onclick="toggle_comment('commentfield');" style="font-family: Verdana, Geneva, sans-serif;font-size:12px;font-weight:bolder;">+ Kommentar abgeben für Englisch Für Anfänger</a>
<BR></BR>
<?php
if(isset($_POST['submitcomment']) && $_POST['submitcomment']=="Submit") {
if((checkComment($_POST['comment']) && strlen($_POST['comment'])>=10 && strlen($_POST['comment'])<=1500)) {
$sqlCmd = "INSERT INTO topmovies.comments
(username,comment,date)
VALUES
('".mysql_real_escape_string($_SESSION['user_username'])."','".mysql_real_escape_string($_POST['comment']);."','".$sqlZeit."')";
$sqlQry = mysql_query($sqlCmd,$sqlHp);
?>
<?PHP
if (!$sqlQry) {
die('Invalid query: ' . mysql_error());
}else { echo'Comment Added!'; }
}else{ echo'Error! Please enter a comment with 30 or more and 1500 or less characters';}
} else { }
?>
<div id="commentfield" style="display:none">
<?PHP
if (isset($_SESSION['user_username'])){
if($getAdmin->status=='BANN'){
echo $lang['BANN'];
exit();
}else{
?>
<form id="postcommentform" method="POST" action="">
<p>Dein Name: <?PHP echo $_SESSION['user_username']; ?></p>
<textarea class="textareacom" name="comment" id="comment" rows="5" cols="20" maxlength="1500" value=""></textarea><br />
<input name="submitcomment" id="submit" type="submit" class="submit" value="Submit" />
</form>
<?PHP
}
}else{
?>
<FORM id="postlogin" action="" method="POST">
<p style="font-weight:bolder;">Um Kommentare schreiben zu können musst du dich zuerst einloggen</p>
<TABLE>
<TR>
<TD align="left"><font face="Arial" color="#000000"><?php echo $lang['REGISTER_USERNAME']; ?></TD>
<TD align="left"><input type="text" name="username"/></TD>
</TR>
<TR>
<TD align="left"><font face="Arial" color="#000000"><?php echo $lang['REGISTER_PASSWORD']; ?></TD>
<TD align="left"><input type="password" name="password"/></TD>
</TR>
<TR>
<TD></TD>
<TD align="left"><input type="submit" id="login" value="login" name="submit" /></TD>
</TR>
</TABLE>
<?php echo $lang['LOGIN_REGISTER']; ?> | <?php echo $lang['FORGOT_PW']; ?>
<BR></BR>
</FORM>
<?PHP
}
?>
</div>
<?php
$sql=mysql_query("select * from topmovies.comments ORDER BY date DESC");
while($row=mysql_fetch_array($sql))
{
$username=$row['username'];
$comment=$row['comment'];
$date=$row['date'];
$name=$row['name'];
?>
<div id="comments" name="comments">
<div class="comments" style="padding-top:5px;">
<BR>
<table width="746px" style="display:inline;" border="0" cellspacing="0" cellpadding="0">
<tr>
<td rowspan="4" valign="top" width="154px" style="padding-right:19px;"><img style="display: block; padding-top:10px;" src="http://img.movie4k.to/img/user_top.gif" height="8px"/>
<span class="test"><?php echo $username; ?><br />
<br />
<font size=1><?PHP echo date("d-m-Y", strtotime($date))?></br>
<?PHP echo date("H:i", strtotime($date))?></font></span>
<img style="display: block; background-color: #AFAFAF; padding-left:10px; padding-right:10px;" src="http://img.movie4k.to/userpics/476090.gif" width=40 height=50/>
<img style="display: block;" src="http://img.movie4k.to/img/user_bottom.gif" height="8px"/></td>
<td colspan="2" valign="bottom" height="8px"><img style="display: block; padding-top:10px;" src="http://img.movie4k.to/img/comment_top2.gif" height="8px"/></td>
</tr>
<tr>
<td rowspan="2" width="522px" class="comment" valign="top" bgcolor="#E3E3E3" style="padding-left:10px; padding-right:17px;">
<?php echo $comment; ?>
</td>
<td width="85px" valign="top" bgcolor="#E3E3E3" style="font-size:19px;">
<div style="min-height:50px;"></div>
</td>
</tr>
<tr>
<td bgcolor="#E3E3E3" valign="bottom"></td>
</tr>
<tr>
<td colspan="2" valign="top" height="8px"><img style="display: block;" src="http://img.movie4k.to/img/comment_bottom2.gif" height="8px"/></td>
</tr>
</table>
</div>
</div>
<BR />
<?php
}
?>
Does anyone see there a mistake what is wrong?
I tryed 1 thing, but then it dont show the echo "comment added!"

Answer 1

After the user submits the form, and after the POST data is read by the php code, you could redir to another page. That could solve it.
if you don't want to do that, you could compare the post with others to see if it has the same content, very close time-stamp, and same user. I wouldn't recommend that though.

Answer 2

Instead of doing
echo'Comment Added!';
You could redirect the user to the same page, thus removing the POST, with a 'flag' which tells the app a comment had just been added.
eg:
header('Location: myPage.php?commentAdded=true'); //myPage is current page
then somewhere else in the page:
if(isset($_GET['commentAdded'])){
echo'Comment Added!';
}