Create simple WordPress plugins


Creating a Simple WordPress Plugin

You can use this as a code snippet for your projects. I am going to create a simple plugin that does nothing but display “Hello World”. I’ll leave the actual functionality of the plugin to you

Create a new php file in your plugin directory called my-hello-world.php, and type the following plugin code:

<?php
/*
Plugin Name: Hello World
Plugin URI: http://lonewolf-online.net/
Description: Sample Hello World Plugin
Author: Tim Trott
Version: 1
Author URI: http://lonewolf-online.net/
*/function sampleHelloWorld()
{
echo “<h2>Hello World</h2>”;
}
?>

The lines inside /* and */ are used by WordPress to find out about the plugin. We have one function called sampleHelloWorld which does exactly that.

Now, traditionally we would have had to open up the sidebar of the theme you are using, find the location of where you want the Hello World displayed, and hard code the function in. Upload to the server and test. If for some reason there is a problem with your plugin (or a third party plugin) then your site would almost certainly stop working. Changing the location from the left to the right sidebar means editing both files accordingly. This isn’t very good.

Widgets

Widgets take away the need for editing the sidebar files of a theme and allow for a drag and drop interface in the admin panel. Lets have a look at how we can wiget enable our plugin.

Open up the Hello World plugin file again and add these lines:

function widget_myHelloWorld() {
?>
<h2 class=”widgettitle”>My Widget Title</h2>
<?php sampleHelloWorld(); ?>
<?php
}function myHelloWorld_init()
{
register_sidebar_widget(__(‘Hello World’), ‘widget_myHelloWorld’);
}
add_action(“plugins_loaded”, “myHelloWorld_init”);

The first function here is what will be displayed on the sidebar when its set-up correctly. Notice that we are calling on our old function. This is upgrading the existing plugin to be widget enabled. You can if you like replace the function call with the function statements and combine the two functions.

The second function is called by WordPress when the plugin is activated. It calls a WordPress function that will register a new widget which will be called “Hello World” which will call our new widget function.

Add action just tells WordPress to call myHelloWorld_init when the plugin is loaded.

Enhancements for Theme Compatibility

While this widget will function fine, we can make some improvements to enable greater theme compatibility – not everyone uses the same themes as you test on.

WordPress will pass parameters to your widget, which contain information about the sidebar and the CSS classes. We should process these parameters and output the correct tags, or you risk breaking some themes.

The first thing we need to do is change our sampleHelloWorld function so that it will accept parameters, then to process these parameters into variables. This is done using the extract function.

function widget_myHelloWorld($args) {
extract($args);
?>
<h2 class=”widgettitle”>My Widget Title</h2>
<?php sampleHelloWorld(); ?>
<?php
}

These two lines will allow us to reference some variables and output correct html structure for the theme being used. The most important variables are before_widget, after_widget, before_title and after_title. Previously we have surrounded the widget title with a hard coded H2 tag with a css class widgettitle, but many themes do not support these tags. They may use a div, or a h1 or a span, so we need our widget to be flexible.

function widget_myHelloWorld($args) {
extract($args);
echo $before_widget;
echo $before_title;?>My Widget Title<?php echo $after_title;
sampleHelloWorld();
echo $after_widget;
}

These changes will allow our plugin to use the same tags as the theme author informs us we need to use, and will allow your widget to look the same as the other widgets in the sidebar.

To configure these options inside a theme, please see the section below on theme support.

Complete Plugin:

<?php
/*
Plugin Name: Hello World
Plugin URI: http://lonewolf-online.net/
Description: Sample Hello World Plugin
Author: Tim Trott
Version: 1
Author URI: http://lonewolf-online.net/
*/function sampleHelloWorld()
{
echo “<h2>Hello World</h2>”;
}function widget_myHelloWorld($args) {
extract($args);
echo $before_widget;
echo $before_title;?>My Widget Title<?php echo $after_title;
sampleHelloWorld();
echo $after_widget;
}

function myHelloWorld_init()
{
register_sidebar_widget(__(‘Hello World’), ‘widget_myHelloWorld’);
}
add_action(“plugins_loaded”, “myHelloWorld_init”);
?>

Testing your Plugin

If you check your plugins page now, you should now have a new plugin listed called Hello World which you can activate. On the Presentation tab, select widgets, and you should see your new widget available to be dragged onto a sidebar. Save your changes and admire your new work.

t is more than likely that your WordPress Widget will need to have some user configurable settings, so why not include a settings form within your widget?These settings pages (admin panels, configuration screen and so on…) are accessed from within the Presentation » Widgets screen from WordPress 2 and from Design » Widgets in WordPress 2.5. When you add a widget to a sidebar, you may notice a little icon on the right hand side of the widget. Clicking on this will open up the widget admin panel where your users can customize your widget to their needs.

Lets use the code from the Hello World widget of the last tutorial and change it around so that we have a settings page. We will see how to create the settings page, how to store/save and retrieve/load settings using the WordPress database and how to handle user inputs.

<?php
/*
Plugin Name: Hello World
Plugin URI: http://lonewolf-online.net/
Description: Sample Hello World Plugin
Author: Tim Trott
Version: 1
Author URI: http://lonewolf-online.net/
*/function sampleHelloWorld()
{
echo “<h2>Hello World</h2>”;
}

 

function widget_myHelloWorld($args) {
extract($args);
echo $before_widget;
echo $before_title;?>My Widget Title<?php echo $after_title;
sampleHelloWorld();
echo $after_widget;
}

function myHelloWorld_init()
{
register_sidebar_widget(__(‘Hello World’), ‘widget_myHelloWorld’);
}
add_action(“plugins_loaded”, “myHelloWorld_init”);
?>

The first thing we are going to create is the icon on the Widget sidebar screen, and get it to open up a blank screen which we will later fill with input controls.

We need to create a function that will be used to display and process the options. The convention is to use the plugin name appended with _control for the control panel page.

function myHelloWorld_control()
{
}

We will come back to this function a bit later on. For now, we will just get WordPress to use our blank form.

In the _init function where we register the sidebar widget, we need to add another function call that will tell WordPress that we have a control panel associated with our plugin.

function myHelloWorld_init()
{
register_sidebar_widget(__(‘Hello World’), ‘widget_myHelloWorld’);
register_widget_control(   ‘Hello World’, ‘myHelloWorld_control’, 300, 200 );
}

This extra function specifies the title of the page, the function that will be called (in this example it does nothing yet) and the widget control panel screen will be 300 pixels wide by 200 pixels tall. You can test this now, or continue and add some content.

WordPress Options

Before we get started on the admin panel, lets first have a look at how we can use the WordPress options database to store values. WordPress has a nice function that will do all the hard work for you called update_option. This function simply takes a key name and the data to store under that key, be it a string, integer or an array. You should try and use a unique, but meaningful, key name to avoid conflicts with other plugins or WordPress itself. I also use a prefix of “widget_” to identify that the settings are for a widget.

The WordPress options database is a table called by default wp_options, and maintains a list of key name and value pairs.

update_options(“widget_myHelloWorld”, “This is a test”);

This will update the key named widget_myHelloWorld in the WordPress database and set the value to “This is a test”. You can retrieve the information at a later date using the get_option function. This function only takes one parameter – the key name to retrieve.

$title = get_option(“widget_myHelloWorld”);
echo $title;

In this example we would expect to see “This is a test” on the screen.

Constructing our Admin Page

I am going to create the admin panel in four stages in this tutorial, you may wish to merge these all into one, or do them in a different order – its entirely up to you.

1. Create the Form Controls

To begin with you are going to need a form design. In this example we are going to simply use a text box and a label. I’ll leave the for design to you!

Each line on the form should be contained within a paragraph block to keep a nice uniform spacing between all elements. By default the items will be centred on the form, so if you need them to be left or right aligned, you will need to specify this in the p tag.

This is the code for my simple html form. You must use unique name and id attributes on the form. You will notice that there is no <form> element in the code. This is because a form element is provided by WordPress which encompass all the widgets that have been loaded.

function myHelloWorld_control()
{
?>
<p>
<label for=”myHelloWorld-WidgetTitle”>Widget Title: </label>
<input type=”text” id=”myHelloWorld-WidgetTitle” name=”myHelloWorld-WidgetTitle” value=”” />
</p>
<?php
}

If you test now you should have a label and text box centred on the widget control form. It is more than likely that you will need more than one form control, however I will let you work on that now you have a grasp of the basics.

2. Get Existing Data and Default Values

The next stage it to populate the form controls with either default values, or values obtained from the database with the get_options function.

Lets get the data from the database, perform a test on it to see if we have valid data, fill the data with default values if necessary then populate the form controls.

function myHelloWorld_control()
{
$options = get_option(“widget_myHelloWorld”);
if (!is_array( $options ))
{
$options = array(
‘title’ => ‘My Widget Title’
);
}?>
<p>
<label for=”myHelloWorld-WidgetTitle”>Widget Title: </label>
<input type=”text” id=”myHelloWorld-WidgetTitle” name=”myHelloWorld-WidgetTitle” value=”<?php echo $options[‘title’];?>” />
</p>
<?php
}

 

The first new line in this code will get the previously stored values from the database. We then test the output variable to see if it is null (no data was retrieved from the database) and if it is we create a new array with one element for the widget title. This method will guarantee that we have a valid value for the title (or an other setting) from the database or a default value. We can then use the title stored in the array to output into the text box value attribute.

3. Get User Input and Store the New Settings

We need some way of capturing the value a user may type in the box and storing it in the database to be re-used. For this we will need another form element that will identify our data when it is submitted. This new element is a hidden value which we will test against.

function myHelloWorld_control()
{
$options = get_option(“widget_myHelloWorld”);
if (!is_array( $options ))
{
$options = array(
‘title’ => ‘My Widget Title’
);
}if ($_POST[‘myHelloWorld-Submit’])
{
$options[‘title’] = htmlspecialchars($_POST[‘myHelloWorld-WidgetTitle’]);
update_option(“widget_myHelloWorld”, $options);
}

 

?>
<p>
<label for=”myHelloWorld-WidgetTitle”>Widget Title: </label>
<input type=”text” id=”myHelloWorld-WidgetTitle” name=”myHelloWorld-WidgetTitle” value=”<?php echo $options[‘title’];?>” />
<input type=”hidden” id=”myHelloWorld-Submit” name=”myHelloWorld-Submit” value=”1″ />
</p>
<?php
}

In this new code segment, we look at the PHP POST variable for an element called myHelloWorld-Submit (the same as the hidden field) and if we found it we extract the widget title from the post variable. It is important to ensure that the code we are about to insert into the database does not contain any malicious code, so we can use the htmlspecialchars function to help prevent SQL injections. We then make a call to update_option to save the new values to the database.

4. Using the Data

What is the point of doing all this and not using the data? None what so ever. Using the data within the widget is just as easy (in fact its the same) as using the data on the form.

In our code that outputs the widget title, you simply need to get the values for the database with get_option, make sure we have valid information and then output the value. We have already seen this in action on the widget control stage, so I will just go straight to the full code listing for this tutorial.

Complete Code

<?php
/*
Plugin Name: Hello World
Plugin URI: http://lonewolf-online.net/
Description: Sample Hello World Plugin
Author: Tim Trott
Version: 2
Author URI: http://lonewolf-online.net/
*/function sampleHelloWorld()
{
echo “<h2>Hello World</h2>”;
}

 

function widget_myHelloWorld($args) {
extract($args);

$options = get_option(“widget_myHelloWorld”);
if (!is_array( $options ))
{
$options = array(
‘title’ => ‘My Widget Title’
);
}

echo $before_widget;
echo $before_title;
echo $options[‘title’];
echo $after_title;

//Our Widget Content
sampleHelloWorld();
echo $after_widget;
}

function myHelloWorld_control()
{
$options = get_option(“widget_myHelloWorld”);<br/>
if (!is_array( $options ))
{
$options = array(
‘title’ => ‘My Widget Title’
);
}

if ($_POST[‘myHelloWorld-Submit’])
{
$options[‘title’] = htmlspecialchars($_POST[‘myHelloWorld-WidgetTitle’]);
update_option(“widget_myHelloWorld”, $options);
}

?>
<p>
<label for=”myHelloWorld-WidgetTitle”>Widget Title: </label>
<input type=”text” id=”myHelloWorld-WidgetTitle” name=”myHelloWorld-WidgetTitle” value=”<?php echo $options[‘title’];?>” />
<input type=”hidden” id=”myHelloWorld-Submit” name=”myHelloWorld-Submit” value=”1″ />
</p>
<?php
}

function myHelloWorld_init()
{
register_sidebar_widget(__(‘Hello World’), ‘widget_myHelloWorld’);
register_widget_control(   ‘Hello World’, ‘myHelloWorld_control’, 300, 200 );
}
add_action(“plugins_loaded”, “myHelloWorld_init”);
?>

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