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PHP - How to detect postback and page refresh

Posted on 2009-05-18
16
1,600 Views
Last Modified: 2012-05-07
I have a php page that posts back to itself. Each time somebody clicks the submit button they get charged a credit. I don't want the customer to pay if they refresh the screen - only if they hit the submit button. How can I distinguish between postback and refresh?

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Question by:lwfuk
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16 Comments
 
LVL 4

Expert Comment

by:trencH87
ID: 24414225
You should at first auto-refresh the site after submit to be sure the end-user don't get charged more credits than he want.

Assuming you have a submit button named "submit", this is the way to check a post.
<?
if (isset($_POST['submit'])) {
    // Charge credit
}
?>

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LVL 4

Expert Comment

by:trencH87
ID: 24414271
Btw, to auto-refresh the site after submit, use this:
<?
if (isset($_POST['submit'])) {
    // Charge credit code here
 
    // Refresh
    header("location: " . $_SERVER['REQUEST_URI']);
}
?>

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Author Comment

by:lwfuk
ID: 24414402
Hi trencH87

Could you test this and tell me what is wrong. It always resisters 'Refresh'

Kind Regards,

Adrian Smith
London


<?php
 
if (isset($_POST['submit'])) {
    echo 'Post';
	header("location: " . $_SERVER['REQUEST_URI']);
} else {
	echo 'Refresh';
}
 
?>
 
<html>
<body>
<form id="f" name="f" method="post" action="<?php $PHP_SELF; ?>">
  <input type="submit" name="button" id="button" value="Submit" />
</form>
</body>
</html>

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LVL 4

Expert Comment

by:trencH87
ID: 24414584
Yup
<?php
 
if (isset($_POST['submit'])) 
{
    
    // Type in the code for charging credits here.
 
    // header() in this case refreshes the site.
    header("location: " . $_SERVER['REQUEST_URI']);
 
} else 
{
    echo 'Form isnt submitted. Please submit the form.';
}
 
?>
 
 
<html>
<body>
<form id="test" name="test" method="post" action="">
  <input type="submit" name="submit" id="button" value="Submit" />
</form>
</body>
</html>

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0
 

Author Comment

by:lwfuk
ID: 24414676
trencH87

It doesn't work. Did you test it?

The example you posted is identical to mine except that you have missed off:

action="<?php $PHP_SELF; ?>"
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LVL 4

Expert Comment

by:trencH87
ID: 24414710
<?php $PHP_SELF; ?> is really unnessasary in this case. And yes, I tested it. Remember that it shouldnt print out anything when submitting the form. The code I gave you just refreshes the site when the form is submitted. Its up to you to implement the function for charging credits.
0
 
LVL 4

Expert Comment

by:trencH87
ID: 24414734
Btw, it wasnt identical. I renamed the input type name to "submit" - or else $_POST['submit'] wouldnt work.
0
 

Author Comment

by:lwfuk
ID: 24414742
The example above continually registers 'Form isnt submitted. Please submit the form.'
0
 

Author Comment

by:lwfuk
ID: 24414771
Take a look again.

ie:  <input type="submit" name="button" id="button" value="Submit" />

Note: type="submit"
0
 
LVL 4

Expert Comment

by:trencH87
ID: 24414852
Just copy&paste this code, and you'll see that it works.

Note: name="submit". the "type" isnt read by $_POST[] - the "name" is.
<?php
 
if (isset($_POST['submit'])) 
{
	// Insert the code for charging credits here.
	
	// header() in this case refreshes the site. 
	//Uncomment this when you want to use it.
    #header("location: " . $_SERVER['REQUEST_URI']);
 
	echo "Form is submitted!";
 
} 
 
?>
 
 
<html>
<body>
<form id="test" name="test" method="post" action="">
  <input type="submit" name="submit" id="button" value="Submit" />
</form>
</body>
</html>

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0
 

Author Comment

by:lwfuk
ID: 24414928
Unfortunatly it still doesn't work.  It prints "Form is submitted!" when you post. It also prints it when you refresh. Test the code below. The counter continually counts whether you refresh or post.


<?php
 
session_start();
 
if (isset($_POST['submit'])) 
{
        // Insert the code for charging credits here.
        
        // header() in this case refreshes the site. 
        //Uncomment this when you want to use it.
    #header("location: " . $_SERVER['REQUEST_URI']);
 
        echo "Form is submitted!";
		
		$_SESSION['count']++;
		
		echo $_SESSION['count'];
		
		
 
} 
 
?>
 
 
<html>
<body>
<form id="test" name="test" method="post" action="">
  <input type="submit" name="submit" id="button" value="Submit" />
</form>
</body>
</html>

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0
 
LVL 4

Expert Comment

by:trencH87
ID: 24415942
Thats what the header is for. Please read up on www.php.net/header
0
 

Author Comment

by:lwfuk
ID: 24416105
Sorry trencH87 but we are just going round in circles.

Do you have a working example? If so, could you post it or if not sombody else reply.

Regards,

Adrian Smith

0
 
LVL 4

Expert Comment

by:trencH87
ID: 24418998
Try this one then.
<?php
session_start();
 
if (isset($_POST['submit'])) 
{
	// Insert the code for charging credits here.
	$_SESSION['count']++;
	
	// header() in this case refreshes the site. 
	//Uncomment this when you want to use it.
	#header("location: " . $_SERVER['REQUEST_URI']);         
 
}
 
echo "Charged points: " . $_SESSION['count'];
 
?>
 
 
<html>
<body>
<p>
<form id="test" name="test" method="post" action="">
  <input type="submit" name="submit" id="button" value="Submit" />
</form>
</p>
</body>
</html>

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0
 
LVL 4

Accepted Solution

by:
trencH87 earned 125 total points
ID: 24419001
Im sorry, this one:
<?php
session_start();
 
if (isset($_POST['submit'])) 
{
	// Insert the code for charging credits here.
	$_SESSION['count']++;
	
	// header() in this case refreshes the site. 
	//Uncomment this when you want to use it.
	header("location: " . $_SERVER['REQUEST_URI']);         
 
}
 
echo "Charged points: " . $_SESSION['count'];
 
?>
 
 
<html>
<body>
<p>
<form id="test" name="test" method="post" action="">
  <input type="submit" name="submit" id="button" value="Submit" />
</form>
</p>
</body>
</html>

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0
 

Author Closing Comment

by:lwfuk
ID: 31582672
Marvellous! Thats what I call a good solution.
Well Done.
0

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