PHP execution order: Header, main page, and footer

Requirements and goal

For this developer tutorial, you should understand how the bluetronix CMS composes a page from its layout, the header, the main page, and the footer. We will show you the order in which the PHP scripts of these areas are executed and which parts of $LayoutHTML are already loaded.

In this example, the basic layout consists of the CMS files bx_Header.html, index.html, and bx_Footer.html. The main page index.html represents the currently called HTML page.

Basic layout: Header, main page, and footer

The basic layout determines the order in which the three areas are included. In the example shown, you will find the layout definition in the table 00_layout.

The relevant excerpt of the layout looks like this:

__DB_Layout_/bx_Header.html__
<main>
   __DB_Layout_Main__
</main>
__DB_Layout_/bx_Footer.html__

The first placeholder includes bx_Header.html. Within the main element, the currently requested page is included via __DB_Layout_Main__, in our example index.html. It is followed by bx_Footer.html.

Although the layout definition contains all three areas, the respective HTML content for the PHP code of the individual areas is loaded gradually into $LayoutHTML.

1. The PHP code of the header is executed first

Open the File Manager and go to the file bx_Header.html. You can edit the PHP code of this area via PHP Code.

The header is the first loaded page area. While its PHP code is executing, $LayoutHTML therefore contains only the HTML from bx_Header.html.

PHP-Code: bx_Header.html

$LayoutHTML enthält:
   bx_Header.html

Here, for example, you can replace placeholders in the header or prepare the navigation. You cannot yet access the actual HTML content of index.html or bx_Footer.html via $LayoutHTML at this point.

2. The PHP code of the main page is executed next

After the header, the CMS loads the called main page, here index.html, and executes its PHP code. At this point, $LayoutHTML contains both the HTML code of the header and the HTML code of the main page.

PHP-Code: index.html

$LayoutHTML enthält:
   bx_Header.html
   index.html

This allows the PHP code of the main page to not only replace its own placeholders but also modify any placeholders already present within the header.

For example: If your header contains the placeholder __HeaderClass__, you can replace it from the main page:

$LayoutHTML = str_replace("__HeaderClass__","active",$LayoutHTML);

Thus, a specific main page can mark its menu item as active within the already loaded header.

The footer has not yet been loaded at this point. Therefore, its HTML content cannot yet be reliably modified via $LayoutHTML.

3. PHP code of the footer is executed last

Finally, the CMS loads bx_Footer.html and executes its PHP code. Now $LayoutHTML contains the HTML content of all three areas.

PHP-Code: bx_Footer.html

$LayoutHTML enthält:
   bx_Header.html
   index.html
   bx_Footer.html

The footer PHP code can therefore replace placeholders within the header, main page, or footer, as long as they are still present at this point.

If the already loaded HTML contains the placeholder __MyTitle__, you can replace it there:

$LayoutHTML = str_replace("__MyTitle__","My Custom Title",$LayoutHTML);

The footer is also suitable for common adjustments that should only be made after loading the entire page structure.

Execution order at a glance

The crucial rule is: PHP can only modify the HTML areas that have already been loaded at this point via $LayoutHTML.

1. bx_Header.html
   PHP sieht: Header
        ↓
2. index.html
   PHP sieht: Header + Hauptseite
        ↓
3. bx_Footer.html
   PHP sieht: Header + Hauptseite + Footer

If, for example, you want to control a header placeholder from a specific page, you would use the PHP code of that main page. If a placeholder should be replaced in all three already loaded areas, the PHP code of the footer that is executed last is a good choice.

Important for your own PHP functions

When defining your own PHP functions in different areas, ensure that the same function is not defined multiple times during a page request. Use unique function names or check if the function already exists before defining it.

if(!function_exists("MyTemplateFunction")) {
   function MyTemplateFunction() {
      return true;
   }
}

Summary

In our basic layout, the PHP code from bx_Header.html runs first, followed by the PHP code from index.html, and finally the PHP code from bx_Footer.html. With each step, the HTML content you can access via $LayoutHTML expands.

Place your PHP code where the necessary HTML sections are already loaded: in the header for header-specific adjustments, in the main page for custom content and the previously loaded header, or in the footer for changes to the already assembled layout.