复选框不会在WP管理员中保持检查状态

I have a list of checkboxes in the WP post dashboard.

The issue is that they don't stay selected after I update the post, so I have to select them again each time:

I tried:

<input type="checkbox" name="industry[]" value="habia" <?php if(isset($_POST['habia'])){echo "checked='checked'";}?> /> habia<br>

or

<input type="checkbox" name="industry[]" value="habia" <?php if(isset($_POST['industry[]'])){echo "checked='checked'";}?> /> habia<br>

or

<input type="checkbox" name="industry[habia]" value="habia" <?php if(isset($_POST['industry']['habia'])){echo "checked='checked'";}?> /> habia<br>

echo $_POST['habia'] doesn't return anything;

My rest of the code:

function industryApprovals(){//the field in the admin section
        global $post;
        $custom = get_post_custom($post->ID);
        $industry = $custom["industry"][0];
        ?>
        <input type="checkbox" name="industry[]" value="habia" <?php if(isset($_POST['habia'])){echo "checked='checked'";}?> /> habia<br>
        <input type="checkbox"/>

        Current values are: 
        <b><?php  
            $industry=unserialize($industry); //looks like wp always returns data from checkboxes serialized
            if($industry == false){ 
                echo "No selected industries.";
            } 
            else{
                $show_values = implode(", ", $industry);
                echo $show_values.'.'; 
            }
        ?></b> 

        <?php
    }

    function save_industry_approvals(){//preserve the data in the admin section
        global $post;
        update_post_meta($post->ID, "industry", $_POST["industry"]);
    }

Thanks!

Solved it by checking the array for the value:

<input type="checkbox" name="industry[]" value="habia" <?php if (in_array("habia", $industry)){echo "checked='checked'";}?> /> habia<br>

Still don't know understand why $_POST did not return anything.