in php, why input form when submit it takes 2 time

问题:

    <?php
        if ($_POST['submit']) {
            mysql_connect ("localhost", "root", "swt") or die ('Error: ' . mysql_error());
            mysql_select_db("db") or die ('Data error:' . mysql_error());
            $text = mysql_real_escape_string($_POST['comments']); 
            $query="INSERT INTO greetings (msg) VALUES ('$text')";
            mysql_query($query) or die ('Error updating database' . mysql_error());
            $id= mysql_insert_id();
            $url = "preview.php?id=".$id;
        }
    ?>
<form method="post" action="<? echo $url ?>" enctype="multipart/form-data" >
    <textarea name="comments" placeholder="please input your message"></textarea>
    <input name="submit" type="submit" value="submit" />
</form>

hello, sorry im newbie in PHP. i want to ask, why when i submit it must takes 2 times pressed before go to the preview.php

thanks.

回答1:

First time the $url is empty so the browser is requesting same page, then the $url is changed, then injected to form so the next post will redirect to your preview.php file.
Just sent header for redirect.

header("Location: /preview.php?id=".$id);

so it will be:

  <?php
        if ($_POST['submit']) {
            mysql_connect ("localhost", "root", "swt") or die ('Error: ' . mysql_error());
            mysql_select_db("db") or die ('Data error:' . mysql_error());
            $text = mysql_real_escape_string($_POST['comments']); 
            $query="INSERT INTO greetings (msg) VALUES ('$text')";
            mysql_query($query) or die ('Error updating database' . mysql_error());
            $id= mysql_insert_id();
            $url = "preview.php?id=".$id;
            header("Location: $url");
        }
    ?>
<form method="post" enctype="multipart/form-data" >
    <textarea name="comments" placeholder="please input your message"></textarea>
    <input name="submit" type="submit" value="submit" />
</form>

Dont use action when you are wanting to send the request to the same page.
(Im assuming the php part in your snippet is the same file)

Also to send the redirect you need to not have html output before sending the header

回答2:

First change <? to <?php like..

<form method="post" action="<?php echo $url ?>" enctype="multipart/form-data" >
<textarea name="comments" placeholder="please input your message"></textarea>
<input name="submit" type="submit" value="submit" />

i like it that way..

Second open the firebug, click on the button and see what is the error you are getting..There is a possibility that you may have some error in the page, or check if your request is initiating or not on the first click. Also check if $url is not empty, on the first click..

回答3:

Change <?= $url?> to <?php echo $ url;?>.

Your server do not have short_open_tags enabled.

回答4:

Your form action value ($url) is generated after first post is submitted, which means it is empty on first submit click. Better solution is to keep action value empty, and in post logic, instead only build $url value you can forward user to $url:

...
  $id= mysql_insert_id();
  $url = "preview.php?id=".$id;
  header('Location: '.$url);
}