[php] Keep values selected after form submission

Consider:

<form method="get" action="">
   <select name="name">
      <option value="a">a</option>
      <option value="b">b</option>
   </select>
   <select name="location">
      <option value="x">x</option>
      <option value="y">y</option>
   </select>
   <input type="submit" value="Submit" class="submit" />
</form>

On submitting the form, how do I make sure that the selected values remain selected in the dropdowns? This form is inside WordPress (PHP).

I don't work in WordPress much, but for forms outside of WordPress, this works well.

PHP

location = "";  // Declare variable

if($_POST) {
    if(!$_POST["location"]) {
        $error .= "Location is required.<br />"; // If not selected, add string to error message
     }else{
        $location = $_POST["location"];          // If selected, assign to variable
     }

HTML

<select name="location">
    <option value="0">Choose...</option>
    <option value="1" <?php if (isset($location) && $location == "1") echo "selected" ?>>location 1</option>
    <option value="2" <?php if (isset($location) && $location == "2") echo "selected" ?>>location 2</option>
</select>

After trying all these "solutions", nothing work. I did some research on W3Schools before and remember there was explanation of keeping values about radio.

But it also works for the Select option. See below for an example. Just try it out and play with it.

<?php
    $example = $_POST["example"];
?>
<form method="post">
    <select name="example">
        <option <?php if (isset($example) && $example=="a") echo "selected";?>>a</option>
        <option <?php if (isset($example) && $example=="b") echo "selected";?>>b</option>
        <option <?php if (isset($example) && $example=="c") echo "selected";?>>c</option>
    </select>
    <input type="submit" name="submit" value="submit" />
</form>

If you are using WordPress (as is the case with the OP), you can use the selected function.

<form method="get" action="">
  <select name="name">
    <option value="a" <?php selected( isset($_POST['name']) ? $_POST['name'] : '', 'a' ); ?>>a</option>
    <option value="b" <?php selected( isset($_POST['name']) ? $_POST['name'] : '', 'b' ); ?>>b</option>
  </select>
  <select name="location">
    <option value="x" <?php selected( isset($_POST['location']) ? $_POST['location'] : '', 'x' ); ?>>x</option>
    <option value="y" <?php selected( isset($_POST['location']) ? $_POST['location'] : '', 'y' ); ?>>y</option>
  </select>
  <input type="submit" value="Submit" class="submit" />
</form>

Just change this line:

 <input type="submit" value="Submit" class="submit" />

with this line:

 <input type="submit" value="Submit/Reload" class="submit" onclick="history.go(-1);">

JavaScript only solution:

var tmpParams = decodeURIComponent(window.location.search.substr(1)).split("&");
for (var i = 0; i < tmpParams.length; i++) {
    var tmparr = tmpParams[i].split("=");
    var tmp = document.getElementsByName(tmparr[0])[0];
    if (!!tmp){
        document.getElementsByName(tmparr[0])[0].value = tmparr[1];
    }
}

Or if you are using jQuery you can replace

 var tmp = document.getElementsByName(tmparr[0])[0];
 if (!!tmp){
     document.getElementsByName(tmparr[0])[0].value = tmparr[1];
 }

with:

 $('*[name="'+tmparr[0]+'"]').val(tmparr[1]);

Since WordPress already uses jQuery you can try something like this:

var POST=<?php echo json_encode($_POST); ?>;
for(k in POST){
  $("#"+k).val(POST[k]);
}

Try this solution for keep selected value in dropdown:

<form action="<?php echo get_page_link(); ?>" method="post">
    <select name="<?php echo $field_key['key']; ?>" onchange="javascript: 
       submit()">
    <option value="">All Category</option>
    <?php 
    foreach( $field['choices'] as $key => $value ){ 
       if($post_key==$key){ ?>
          <option value="<?php echo $key; ?>" selected><?php echo $value; ?></option>
<?php
   }else{?>
  <option value="<?php echo $key; ?>"><?php echo $value; ?></option>
 <?php }
  }?>
 </select>
</form>

This works for me!

<label for="reason">Reason:</label>
<select name="reason" size="1" id="name" >
    <option value="NG" selected="SELECTED"><?php if (!(strcmp("NG", $_POST["reason"]))) {echo "selected=\"selected\"";} ?>Selection a reason below</option>
    <option value="General"<?php if (!(strcmp("General", $_POST["reason"]))) {echo "selected=\"selected\"";} ?>>General Question</option>
    <option value="Account"<?php if (!(strcmp("Account", $_POST["reason"]))) {echo "selected=\"selected\"";} ?>>Account Question</option>
    <option value="Other"<?php if (!(strcmp("Other", $_POST["reason"]))) {echo "selected=\"selected\"";} ?>>Other</option>

</select>

<select name="name">
   <option <?php if ($_GET['name'] == 'a') { ?>selected="true" <?php }; ?>value="a">a</option>
   <option <?php if ($_GET['name'] == 'b') { ?>selected="true" <?php }; ?>value="b">b</option>
</select>

<form method="get" action="">
 <select name="name" value="<?php echo $_GET['name'];?>">
   <option value="a">a</option>
   <option value="b">b</option>
 </select>
 <select name="location" value="<?php echo $_GET['location'];?>">
   <option value="x">x</option>
   <option value="y">y</option>
 </select>
   <input type="submit" value="Submit" class="submit" />
</form>