Complete WordPress Theme & Plugin Development Course

In this lesson we introduce this section on PHP for WordPress and go over what we will learn in the coming lessons:

• Explain what PHP is and how it works
• Write some PHP and learning the basics of the language
• Introduce important WordPress specific PHP things that are important to know about, like the Loop, Template Tags, and Hooks

Next up we answer the question, "What is PHP?"

In this lesson we learn the PHP stands for "PHP: Hypertext Preprocessor" and runs before the HTML for a web page is generated.  PHP runs a lot in WordPress and can be used outside of WordPress as well to build sites and applications.

PHP Review:

• PHP is a programming language
• It runs on the server before HTML is sent to the browser
• PHP is used quite a lot in WordPress itself and in WordPress Development
• PHP can also be used outside of WordPress in other applications and web sites

Next up we practice writing some PHP.

In this lesson we start to write some basic PHP.

Covered in this lesson:

• Opening an index.php file
• Writing a variable
• Echoing a variable
• Echoing a string of text
• Concatenating or combining variables and strings

Next up we learn some more PHP Programming Basics.

In text lesson we outline some of the basics of working with PHP that are important for us to know going forward.  Read through and absorb what you can and in the next lesson we will look at putting some of this into practice.

In this lesson we work on the following practice exercise:

1. Activate theme 1.4 PHP Basics (Starter)
2. Create an array of post titles
3. Loop through the array of posts
4. Inside of the Loop, call a display_title() function and pass it the title as a parameter
5. Have the display_title() function echo the title in an <h3> tag

Try practicing this on your own before checking out the completed solution and the walk through in the video.

In this lesson we learn about the WordPress Coding Standards.  

These are guidelines and suggestions for how to write and format your PHP when working with WordPress.

You can access the WordPress PHP Coding Standards here: https://make.wordpress.org/core/handbook/best-practices/coding-standards/php/

The WordPress Coding Standards contain information around the following topics:

• Single and Double Quotes
• Indentation
• Brace Style
• Use elseif, not else if
• Regular Expressions
• No Shorthand PHP Tags
• Remove Trailing Spaces
• Space Usage
• Formatting SQL statements
• Database Queries
• Naming Conventions
• Self-Explanatory Flag Values for Function Arguments
• Interpolation for Naming Dynamic Hooks
• Ternary Operator
• Yoda Conditions
• Clever Code
• Error Control Operator @
• Don’t extract()

Not all of these may make sense to you at this point so try taking a read through these now and check back on them again at different points in the course.

In general you will find three general types of PHP files in WordPress:

1. WordPress Core Files - These control how WordPress works, not edited, but interesting and possibly helpful to read through or study.
2. WordPress Theme Files - These control how themes work and display content.  When you are building or customizing a child theme you will definitely edit these files.
3. WordPress Plugin Files - These are used when building plugins.  If you are writing your own plugin or extending another plugin you will edit these files, but you would not generally directly edit the code of another plugin.
4. Include Files - Small PHP files that are included in larger files appear in Core, Theme and Plugin files.  You will likely come across and write them yourself.

The Loop is a combination of a conditional statement and loop that intelligently gathers and prepares post or page content to display.

It consists of the following:

1. A PHP If Statement
2. A PHP While Loop
3. A special WordPress function call to get the correct post or page (or custom post etc)

A basic loop looks like this:

```

    <?php if ( have_posts() ) : while ( have_posts() ) : the_post(); ?>

      <h2><?php the_title(); ?></h2>
      <?php the_content(); ?>

    <?php endwhile; else: ?>

      <h2><?php esc_html_e( '404 Error', 'phpforwp' ); ?></h2>
      <p><?php esc_html_e( 'Sorry, content not found.', 'phpforwp' ); ?></p>

    <?php endif; ?>

```

Notice that since the PHP code is inside various self contained PHP blocks, it is also possible to use HTML inside of the Loop.

It is also possible though to have a pure PHP loop without any HTML being included between PHP blocks:

```

<?php if ( have_posts() ) : while ( have_posts() ) : the_post(); 

     the_title( ’<h1>', ’</h1>' ); 

     the_content();

endwhile; else: 

     _e( 'Sorry, no pages matched your criteria.', 'textdomain' ); 

endif; ?>

```

It is also possible to customize the Loop, which we will look at late in the course.

Now it's time to practice using PHP Loop on your own:

1. Activate theme 1.8 – The Loop (Starter) 
2. Open index.php
3. Code out The Loop
4. Use the_title and the_content to display the content
5. Display a 404 message using _e() if no content available
6. Open a page or post from WP Admin to test

Try tackling this on your own then follow along with me as I show you the approach I took.

Template tags are special functions that allow us to easily get information and content from WordPress.

Some popular template tags include:

• get_header()
• get_footer()
• get_sidebar()
• get_template_part()
• wp_login_form()
• bloginfo()
• the_title()
• get_the_title()
• the_content()
• the_author()
• the_category()
• the_tags()
• comment_author()
• the_post_thumbnail()
• the_permalink()
• edit_post_link()
• site_url()
• wp_nav_menu()

Now that we've learned about template tags, it's time for you to tackle some practice on your own:

1. Activate theme 1.10 – Template Tags (Starter) 
2. Open index.php
3. Add template tags inside The Loop
4. Add template tags outside The Loop
5. See how many different template tags you can get working!

After you take a stab on your own, you can follow along with my solution :)

Conditional Tags are WordPress functions that return true when certain conditions are met.

Some common conditional tags include:

• is_front_page()
• is_home()
• is_admin()
• is_single()
• is_single( 'slug' )
• is_single( [ 'slug-1', 'slug-2', 'slug-3' ] )
• is_singular()
• get_post_type()
• has_excerpt()
• is_page()
• is_page( 'slug' )
• is_page( [ 'slug-1', 'slug-2', 'slug-3' ] )
• is_page_template( 'custom.php' )
• comments_open()
• is_category()
• is_tag()
• is_archive()
• in_the_loop()

Now that you've learned about Conditional Tags, let's try practicing writing some:

1. Activate theme 1.12 – Conditional Tags (Starter) 
2. Open index.php
3. Try adding conditional tags
4. Open page from admin or visit site.dev/category site.dev/tag url directly
5. Might need && || !

Hooks allow you to add custom code into existing software.

Two types of hooks exist in WordPress:

1. Action Hooks let you run your own code when certain events take place in the WordPress run cycle.
2. Filter Hooks let you modify how content is displayed on a page or saved to the database.

Here is an example of an Action Hook in use:

```

<?php 

function my_theme_styles() { 

     wp_enqueue_style( 'main-css', get_stylesheet_uri() );

}

add_action( 'wp_enqueue_scripts', 'my_theme_styles' );

?> 

```

Here is an example of a Filter Hook in use:

```

<?php 

function my_read_more_link( $excerpt ) { 

     return $excerpt . '<a href="' . get_permalink() . '">Read more</a>'; 

} 

add_filter( 'get_the_excerpt', 'my_read_more_link', 10 );

?> 

```

Now it's time to practice writing some hooks on your own. 

Try the following:

1. Activate 1.14 – WordPress Hooks (Starter)
2. Open the functions.php
3. Try enqueueing the theme CSS via an Action Hook
4. Try adding a Read More link to the_excerpt() with a filter

Some important points for review:

• PHP is a server side programming language.
• Many Core, Plugin and Theme
  files in WordPress are PHP.
• Some basic PHP is required for WordPress Development.
• WordPress provides The Loop, Template Tags and Conditionals to make writing PHP easier.
• Action and Filter Hooks let us run our own code and modify data in WordPress programmatically.

A Child Theme allows you to override another theme (parent theme) without making direct changes that are lost during updates.

A Starter Theme includes helpful files and functions for building themes from scratch.  You usually edit starter themes directly, not using child themes.

Here is when to use each:

• Child Theme - Customizing an existing  theme
• Starter Theme - Building sites from scratch

Child Theme

1. Reference to parent theme in style.css file
2. Include parent style in functions.php file
3. Copies of any templates from Parent Theme you want to modify

Parent Theme

1. Keeps all original files unedited
2. Before loading a file, WordPress looks to see if exists in Child Theme
3. Can be updated without affecting code in Child Theme

In this lesson we take a look at a child theme in action.

Now it is time for you to practice making a child theme:

1. Pick a WordPress theme
2. Create a Child Theme for it
3. Modify the CSS and one of the templates
4. You don’t need to make it look better, just get it working!
5. Demo and Practice Child Theme files 

Starter Theme Basics:

1. Include common theme template files
2. No CSS styles (but some include Bootstrap / Foundation)
3. Extra functionality in functions.php
4. Extra hooks in template files
5. Follow modular file architecture
6. Some include workflow tools
7. Usually edited directly, not via child themes

In this lesson I encourage you to go practice working with a starter theme on your own:

1. Choose a starter theme (I recommend JointsWP)
2. Install and Activate it
3. Make a CSS change
4. Make a change to one of the templates
5. WARNING: Not all starter themes are created equal

Child Theme Review:

• When customizing a theme use a Child Theme
• When starting from scratch use a Starter Theme
• Also possible to start with no child theme or starter theme!