# How to extend the CMS interface #

## Introduction ##

The CMS interface works just like any other part of your website: It consists of
PHP controllers, templates, CSS stylesheets and JavaScript. Because it uses the
same base elements, it is relatively easy to extend.

As an example, we're going to add a permanent "bookmarks" link list to popular pages
into the main CMS menu. A page can be bookmarked by a CMS author through a
simple checkbox.

For a deeper introduction to the inner workings of the CMS, please refer to our
guide on [CMS Architecture](/developer_guides/customising_the_admin_interface/cms_architecture).

## Redux Devtools

It's important to be able to view the state of the React application when you're debugging and
building the interface.

To be able to view the state, you'll need to be in a dev environment 
and have the [Redux Devtools](https://github.com/zalmoxisus/redux-devtools-extension)
installed on Google Chrome or Firefox, which can be found by searching with your favourite search
engine.

## Overload a CMS template ##

If you place a template with an identical name into your application template
directory (usually `mysite/templates/`), it'll take priority over the built-in
one.

CMS templates are inherited based on their controllers, similar to subclasses of
the common `Page` object (a new PHP class `MyPage` will look for a `MyPage.ss` template).
We can use this to create a different base template with `LeftAndMain.ss`
(which corresponds to the `LeftAndMain` PHP controller class).

Copy the template markup of the base implementation at `framework/admin/templates/Includes/LeftAndMain_Menu.ss`
into `mysite/templates/Includes/LeftAndMain_Menu.ss`. It will automatically be picked up by
the CMS logic. Add a new section into the `<ul class="cms-menu-list">`

	:::ss
	...
	<ul class="cms-menu-list">
		<!-- ... -->
		<li class="bookmarked-link first">
			<a href="{$AdminURL}pages/edit/show/1">Edit "My popular page"</a>
		</li>
		<li class="bookmarked-link last">
			<a href="{$AdminURL}pages/edit/show/99">Edit "My other page"</a>
		</li>
	</ul>
	...

Refresh the CMS interface with `admin/?flush=all`, and you should see those
hardcoded links underneath the left-hand menu. We'll make these dynamic further down.

## Include custom CSS in the CMS

In order to show the links a bit separated from the other menu entries,
we'll add some CSS, and get it to load
with the CMS interface. Paste the following content into a new file called
`mysite/css/BookmarkedPages.css`:

	:::css
	.bookmarked-link.first {margin-top: 1em;}

Load the new CSS file into the CMS, by setting the `LeftAndMain.extra_requirements_css`
[configuration value](../../configuration).

	:::yml
	LeftAndMain:
	  extra_requirements_css:
	    - mysite/css/BookmarkedPages.css

## Create a "bookmark" flag on pages ##

Now we'll define which pages are actually bookmarked, a flag that is stored in
the database. For this we need to decorate the page record with a
`DataExtension`. Create a new file called `mysite/code/BookmarkedPageExtension.php`
and insert the following code.

	:::php
	<?php

	class BookmarkedPageExtension extends DataExtension {

		private static $db = array(
			'IsBookmarked' => 'Boolean'
		);

		public function updateCMSFields(FieldList $fields) {
			$fields->addFieldToTab('Root.Main',
				new CheckboxField('IsBookmarked', "Show in CMS bookmarks?")
			);
		}
	}

Enable the extension in your [configuration file](../../configuration)

	:::yml
	SiteTree:
	  extensions:
	    - BookmarkedPageExtension

In order to add the field to the database, run a `dev/build/?flush=all`.
Refresh the CMS, open a page for editing and you should see the new checkbox.

## Retrieve the list of bookmarks from the database

One piece in the puzzle is still missing: How do we get the list of bookmarked
pages from the database into the template we've already created (with hardcoded
links)? Again, we extend a core class: The main CMS controller called
`LeftAndMain`.

Add the following code to a new file `mysite/code/BookmarkedLeftAndMainExtension.php`;

	:::php
	<?php

	class BookmarkedPagesLeftAndMainExtension extends LeftAndMainExtension {

		public function BookmarkedPages() {
			return Page::get()->filter("IsBookmarked", 1);
		}
	}

Enable the extension in your [configuration file](../../configuration)

	:::yml
	LeftAndMain:
	  extensions:
	    - BookmarkedPagesLeftAndMainExtension

As the last step, replace the hardcoded links with our list from the database.
Find the `<ul>` you created earlier in `mysite/admin/templates/LeftAndMain.ss`
and replace it with the following:

	:::ss
	<ul class="cms-menu-list">
		<!-- ... -->
		<% loop $BookmarkedPages %>
		<li class="bookmarked-link $FirstLast">
			<li><a href="{$AdminURL}pages/edit/show/$ID">Edit "$Title"</a></li>
		</li>
		<% end_loop %>
	</ul>

## Extending the CMS actions

CMS actions follow a principle similar to the CMS fields: they are built in the
backend with the help of `FormFields` and `FormActions`, and the frontend is
responsible for applying a consistent styling.

The following conventions apply:

* New actions can be added by redefining `getCMSActions`, or adding an extension
with `updateCMSActions`.
* It is required the actions are contained in a `FieldSet` (`getCMSActions`
returns this already).
* Standalone buttons are created by adding a top-level `FormAction` (no such
button is added by default).
* Button groups are created by adding a top-level `CompositeField` with
`FormActions` in it.
* A `MajorActions` button group is already provided as a default.
* Drop ups with additional actions that appear as links are created via a
`TabSet` and `Tabs` with `FormActions` inside.
* A `ActionMenus.MoreOptions` tab is already provided as a default and contains
some minor actions.
* You can override the actions completely by providing your own
`getAllCMSFields`.

Let's walk through a couple of examples of adding new CMS actions in `getCMSActions`.

First of all we can add a regular standalone button anywhere in the set. Here
we are inserting it in the front of all other actions. We could also add a
button group (`CompositeField`) in a similar fashion.

	:::php
	$fields->unshift(FormAction::create('normal', 'Normal button'));

We can affect the existing button group by manipulating the `CompositeField`
already present in the `FieldList`.

	:::php
	$fields->fieldByName('MajorActions')->push(FormAction::create('grouped', 'New group button'));

Another option is adding actions into the drop-up - best place for placing
infrequently used minor actions.

	:::php
	$fields->addFieldToTab('ActionMenus.MoreOptions', FormAction::create('minor', 'Minor action'));

We can also easily create new drop-up menus by defining new tabs within the
`TabSet`.

	:::php
	$fields->addFieldToTab('ActionMenus.MyDropUp', FormAction::create('minor', 'Minor action in a new drop-up'));

<div class="hint" markdown='1'>
Empty tabs will be automatically removed from the `FieldList` to prevent clutter.
</div>

To make the actions more user-friendly you can also use alternating buttons as
detailed in the [CMS Alternating Button](cms_alternating_button)
how-to.

## ReactJS in SilverStripe

### SilverStripeComponent

The base class for SilverStripe React components. If you're building React components for the CMS, this is the class you want to extend. `SilverStripeComponent` extends `React.Component` and adds some handy CMS specific behaviour.

### Creating a component

__my-component.js__
```javascript
import SilverStripeComponent from 'silverstripe-component';

class MyComponent extends SilverStripeComponent {

}

export default MyComponent;
```

That's how you create a SilverStripe React component!

### Interfacing with legacy CMS JavaScript

One of the great things about ReactJS is that it works great with DOM based libraries like jQuery and Entwine. To allow legacy-land scripts to notify your React component about changes, add the following.

__my-component.js__
```javascript
import SilverStripeComponent from 'silverstripe-component';

class MyComponent extends SilverStripeComponent {
	componentDidMount() {
		super.componentDidMount();
	}
	
	componentWillUnmount() {
		super.componentWillUnmount();
	}
}

export default MyComponent;
```

This is functionally no different from the first example. But it's a good idea to be explicit and add these `super` calls now. You will inevitably add `componentDidMount` and `componentWillUnmount` hooks to your component and it's easy to forget to call `super` then.

So what's going on when we call those? Glad you asked. If you've passed `cmsEvents` into your component's `props`, wonderful things will happen.

Let's take a look at some examples.

### Getting data into a component

Sometimes you'll want to call component methods when things change in legacy-land. For example when a CMS tab changes you might want to update some component state.

__main.js__
```javascript
import $ from 'jquery';
import React, { PropTypes, Component } from 'react';
import MyComponent from './my-component';

$.entwine('ss', function ($) {
	$('.my-component-wrapper').entwine({
		getProps: function (props) {
			var defaults = {
				cmsEvents: {
					'cms.tabchanged': function (event, title) {
						// Call a Redux action to update state.
					}
				}
			};
			
			return $.extend(true, defaults, props);
		},
		onadd: function () {
			var props = this.getProps();
			
			React.render(
				<MyComponent {...props} />,
				this[0]
			);
		}
	});
});
```

__legacy.js__
```javascript
(function ($) {
	$.entwine('ss', function ($) {
		$('.cms-tab').entwine({
			onclick: function () {
				$(document).trigger('cms.tabchanged', this.find('.title').text());
			}
		});
	});
}(jQuery));
```

Each key in `props.cmsEvents` gets turned into an event listener by `SilverStripeComponent.componentDidMount`. When a legacy-land script triggers that event on `document`, the associated component callback is invoked, with the component's context bound to it.

All `SilverStripeComponent.componentWillUnmount` does is clean up the event listeners when they're no longer required.

There are a couple of important things to note here:

1. Both files are using the same `ss` namespace.
2. Default properties are defined using the `getProps` method.

This gives us the flexibility to add and override event listeners from legacy-land. We're currently updating the current tab's title when `.cms-tab` is clicked. But say we also wanted to highlight the tab. We could do something like this.

__legacy.js__
```javascript
(function ($) {
	$.entwine('ss', function ($) {
		$('.main .my-component-wrapper').entwine({
			getProps: function (props) {
				return this._super({
					cmsEvents: {
						'cms.tabchanged': function (event, title) {
							// Call a Redux action to update state.
						}
					}
				});
			}
		});
		
		$('.cms-tab').entwine({
			onclick: function () {
				$(document).trigger('cms.tabchanged', this.find('.title').text());
			}
		});
	});
}(jQuery));
```

Here we're using Entwine to override the `getProps` method in `main.js`. Note we've made the selector more specific `.main .my-component-wrapper`. The most specific selector comes first in Entwine, so here our new `getProps` gets called, which passes the new callback to the `getProps` method defined in `main.js`.

### Getting data out of a component

There are times you'll want to update things in legacy-land when something changes in you component.

`SilverStripeComponent` has a handly method `emitCmsEvents` to help with this.

__my-component.js__
```javascript
import SilverStripeComponent from 'silverstripe-component';

class MyComponent extends SilverStripeComponent {
	componentDidMount() {
		super.componentDidMount();
	}
	
	componentWillUnmount() {
		super.componentWillUnmount();
	}
	
	componentDidUpdate() {
		this.emitCmsEvent('my-component.title-changed', this.state.title);
	}
}

export default MyComponent;
```

__legacy.js__
```javascript
(function ($) {
	$.entwine('ss', function ($) {
		$('.cms-tab').entwine({
			onmatch: function () {
				var self = this;

				$(document).on('my-component.title-changed', function (event, title) {
					self.find('.title').text(title);
				});
			},
			onunmatch: function () {
				$(document).off('my-component.title-changed');
			}
		});
	});
}(jQuery));
```

### Implementing handlers

Your newly created buttons need handlers to bind to before they will do anything.
To implement these handlers, you will need to create a `LeftAndMainExtension` and add
applicable controller actions to it:

	:::php
	class CustomActionsExtension extends LeftAndMainExtension {
		
		private static $allowed_actions = array(
        	'sampleAction'
    	);
    	
    	public function sampleAction()
    	{
    		// Create the web
    	}
    	
    }
    
The extension then needs to be registered:

	:::yaml
	LeftAndMain:
		extensions:
			- CustomActionsExtension
			
You can now use these handlers with your buttons:

	:::php
	$fields->push(FormAction::create('sampleAction', 'Perform Sample Action'));

## Summary

In a few lines of code, we've customised the look and feel of the CMS.

While this example is only scratching the surface, it includes most building
blocks and concepts for more complex extensions as well.

## Related

 * [Reference: CMS Architecture](../cms_architecture)
 * [Reference: Layout](../cms_layout)
 * [Rich Text Editing](/developer_guides/forms/field_types/htmleditorfield)
 * [CMS Alternating Button](cms_alternating_button)