Agile UI is a component framework, which follows a software patterns known as “render tree” and “two pass HTML rendering”.

class Atk4\Ui\View

A View is a most fundamental object that can take part in the render tree. All of the other components descend from the View class.

View object is recursive. You can take one view and add another View inside of it:

$v = new \Atk4\Ui\View(['ui' => 'segment', 'class.inverted' => true]);
Button::addTo($v, ['Orange', 'class.inverted orange' => true]);

The above code will produce the following HTML block:

<div class="ui inverted segment">
    <button class="ui inverted orange button">Orange</button>

All of the views combined form a “render tree”. In order to get the HTML output from all the render tree Views you need to execute renderToHtml() for the top-most leaf:

echo $v->renderToHtml();

Each of the views will automatically render all of the child views.

Initializing Render Tree

Views use a principle of delayed init, which allow you to manipulate View objects in any way you wish, before they will actuallized.

Atk4\Ui\View::add($object, $region = 'Content')

Add child view as a parent of the this view.

In addition to adding a child object, sets up it’s template and associate it’s output with the region in our template.

Will copy $this->getApp() into $object->getApp().

If this object is initialized, will also initialize $object

  • $object – Object or Seed to add into render tree.

  • $region – When outputting HTML, which region in View::$template to use.


View will automatically execute an init() method. This will happen as soon as values for properties properties app, id and path can be determined.

You should override init method for composite views, so that you can add() additional sub-views into it.

In the next example I’ll be creating 3 views, but it at the time their __constructor is executed it will be impossible to determine each view’s position inside render tree:

$middle = new \Atk4\Ui\View(['ui' => 'segment', '' => true]);
$top = new \Atk4\Ui\View(['ui' => 'segments']);
$bottom = new \Atk4\Ui\Button(['Hello World', '' => true]);

// not arranged into render-tree yet


// still not sure if finished adding

$app = new \Atk4\Ui\App('My App');

// calls init() for all elements recursively

Each View’s init() method will be executed first before calling the same method for child elements. To make your execution more straightforward we recommend you to create App class first and then continue with Layout initialization:

$app = new \Atk4\Ui\App('My App');
$top = $app->initLayout(new \Atk4\Ui\View(['ui' => 'segments']));

$middle = View::addTo($top, ['ui' => 'segment', '' => true]);

$bottom = Button::addTo($middle, ['Hello World', '' => true]);

Finally, if you prefer a more consise code, you can also use the following format:

$app = new \Atk4\Ui\App('My App');
$top = $app->initLayout([\Atk4\Ui\View::class, 'ui' => 'segments']);

$middle = View::addTo($top, ['ui' => 'segment', '' => true]);

$bottom = Button::addTo($middle, ['Hello World', '' => true]);

The rest of documentation will use this concise code to keep things readable, however if you value type-hinting of your IDE, you can keep using “new” keyword. I must also mention that if you specify first argument to add() as a string it will be passed to Factory::factory(), which will be responsible of instantiating the actual object.

(TODO: link to App:Factory)

Use of $app property and Dependency Injeciton

property Atk4\Ui\View::$app

Each View has a property $app that is defined through \Atk4\Core\AppScopeTrait. View elements rely on persistence of the app class in order to perform Dependency Injection.

Consider the following example:

$app->logger = new Logger('log'); // Monolog

// next, somewhere in a render tree
$view->getApp()->logger->log('Foo Bar');

Agile UI will automatically pass your $app class to all the views.

Integration with Agile Data


Associate current view with a domain model.

property Atk4\Ui\View::$model

Stores currently associated model until time of rendering.

If you have used Agile Data, you should be familiar with a concept of creating Models:

$db = new \Atk4\Data\Persistence\Sql($dsn);

$client = new Client($db); // extends \Atk4\Data\Model

Once you have a model, you can associate it with a View such as Form or Grid so that those Views would be able to interact with your persistence directly:


In most environments, however, your application will rely on a primary Database, which can be set through your $app class:

$app->db = new \Atk4\Data\Persistence\Sql($dsn);

// next, anywhere in a view
$client = new Client($this->getApp()->db);

Or if you prefer a more consise code:

$app->db = new \Atk4\Data\Persistence\Sql($dsn);

// next, anywhere in a view

Again, this will use Factory feature of your application to let you determine how to properly initialize the class corresponding to string ‘Client’.

UI Role and Classes

Atk4\Ui\View::__construct($defaults = [])
  • $defaults – set of default properties and classes.

property Atk4\Ui\View::$ui

Indicates a role of a view for CSS framework.

A constructor of a view often maps into a <div> tag that has a specific role in a CSS framework. According to the principles of Agile UI, we support a wide varietty of roles. In some cases, a dedicated object will exist, for example a Button. In other cases, you can use a View and specify a UI role explicitly:

$view = View::addTo($app, ['ui' => 'segment']);

If you happen to pass more key/values to the constructor or as second argument to add() they will be treated as default values for the properties of that specific view:

$view = View::addTo($app, ['ui' => 'segment', 'name' => 'test-id']);

For a more IDE-friendly format, however, I recommend to use the following syntax:

$view = View::addTo($app, ['ui' => 'segment']);
$view->name = 'test-id';

You must be aware of a difference here - passing array to constructor will override default property before call to init(). Most of the components have been designed to work consistently either way and delay all the property processing until the render stage, so it should be no difference which syntax you are using.

If you are don’t specify key for the properties, they will be considered an extra class for a view:

$view = View::addTo($app, ['' => true, 'ui' => 'segment']);
$view->name = 'test-id';

You can either specify multiple classes one-by-one or as a single string “inverted orange”.

property Atk4\Ui\View::$class

List of classes that will be added to the top-most element during render.


Add CSS class to element. Previously added classes are not affected. Multiple CSS classes can also be added if passed as space separated string or array of class names.

  • $class (string|array) – CSS class name or array of class names



  • $class – string|array one or multiple classes to be removed.

In addition to the UI / Role classes during the render, element will receive extra classes from the $class property. To add extra class to existing object:

$button->addClass('blue large');

Classes on a view will appear in the following order: “ui blue large button”

Special-purpose properties

A view may define a special-purpose properties, that may modify how the view is rendered. For example, Button has a property ‘icon’, that is implemented by creating instance of \Atk4\Ui\Icon() inside the button.

The same pattern can be used for other scenarios:

$button = Button::addTo($app, ['icon' => 'book']);

This code will have same effect as:

$button = Button::addTo($app);
$button->icon = 'book';

During the Render of a button, the following code will be executed:

Icon::addTo($button, ['book']);

If you wish to use a different icon-set, you can change Factory’s route for ‘Icon’ to your own implementation OR you can pass icon as a view:

$button = Button::addTo($app, ['icon' => new MyAwesomeIcon('book')]);

Rendering of a Tree


Perform render of this View and all the child Views recursively returning a valid HTML string.

Any view has the ability to render itself. Once executed, render will perform the following:

  • call renderView() of a current object.

  • call recursiveRender() to recursively render sub-elements.

  • return JS code with on-dom-ready instructions along with HTML code of a current view.

You should not override renderToHtml() in your objects. If you are integrating Agile UI into your framework you shouldn’t even use renderToHtml(), but instead use getHtml and getJs.


Returns HTML for this View as well as all the child views.


Returns JsBlock containing JS chains that were assigned to current element or it’s children.

Modifying rendering logic

When you creating your own View, you most likely will want to change it’s rendering mechanics. The most suitable location for that is inside renderView method.


Perform necessary changes in the $template property according to the presentation logic of this view.

You should override this method when necessary and don’t forget to execute parent::renderView():

protected function renderView(): void
    if (str_len($this->info) > 100) {


It’s important when you call parent. You wouldn’t be able to affect template of a current view anymore after calling renderView.

Also, note that child classes are rendered already before invocation of rederView. If you wish to do something before child render, override method View::recursiveRender()

property Atk4\Ui\View::$template

Template of a current view. This attribute contains an object of a class HtmlTemplate. You may secify this value explicitly:

View::addTo($app, ['template' => new \Atk4\Ui\HtmlTemplate('<b>hello</b>')]);
property Atk4\Ui\View::$defaultTemplate

By default, if value of View::$template is not set, then it is loaded from class specified in defaultTemplate:

View::addTo($app, ['defaultTemplate' => './mytpl.html']);

You should specify defaultTemplate using relative path to your project root or, for add-ons, relative to a current file:

// in Add-on
View::addTo($app, ['defaultTemplate' => __DIR__ . '/../templates/mytpl.httml']);

Agile UI does not currently provide advanced search path for templates, by default the template is loaded from folder vendor/atk4/ui/template. To change this behaviour, see App::loadTemplate().

property Atk4\Ui\View::$region

Name of the region in the owner’s template where this object will output itself. By default ‘Content’.

Here is a best practice for using custom template:

class MyView extends View
    public $template = 'custom.html';

    public $title = 'Default Title';

    protected function renderView(): void

        $this->template->set('title', $this->title);

As soon as the view becomes part of a render-tree, the HtmlTemplate object will also be allocated. At this point it’s also possible to override default template:

MyView::addTo($app, ['template' => $template->cloneRegion('MyRegion')]);

Or you can set $template into object inside your constructor, in which case it will be left as-is.

On other hand, if your ‘template’ property is null, then the process of adding View inside RenderTree will automatically clone region of a parent.

Lister is a class that has no default template, and therefore you can add it like this:

$profile = View::addTo($app, ['template' => 'myview.html']);
Lister::addTo($profile, [], ['Tags'])->setModel($user->ref('Tags'));

In this set-up a template myview.html will be populated with fields from $user model. Next, a Lister is added inside Tags region which will use the contents of a given tag as a default template, which will be repeated according to the number of referenced ‘Tags’ for given users and re-inserted back into the ‘Tags’ region.

See also HtmlTemplate.

Unique ID tag

property Atk4\Ui\View::$region

ID to be used with the top-most element.

Agile UI will maintain unique ID for all the elements. The tag is set through ‘name’ property:

$b = new \Atk4\Ui\Button(['name' => 'my-button3']);
echo $b->renderToHtml();


<div class="ui button" id="my-button3">Button</div>

If ID is not specified it will be set automatically. The top-most element of a render tree will use id=atk and all of the child elements will create a derived ID based on it’s UI role.


If role is unspecified then ‘view’ will be used. The main benefit here is to have automatic allocation of all the IDs throughout the render-tree ensuring that those ID’s are consistent between page requests.

It is also possible to set the “last” bit of the ID postfix. When Form controls are populated, the name of the field will be used instead of the role. This is done by setting ‘name’ property.

property Atk4\Ui\View::$name

Specify a name for the element. If container already has object with specified name, exception will be thrown.

Reloading a View


Agile UI makes it easy to reload any View on the page. Starting with v1.4 you can now use View::JsReload(), which will respond with JavaScript Action for reloading the view:

$b1 = Button::addTo($app, ['Click me']);
$b2 = Button::addTo($app, ['Rand: ' . rand(1, 100)]);

$b1->on('click', $b2->jsReload());

// previously:
// $b1->on('click', new \Atk4\Ui\Js\JsReload($b2));

Modifying Basic Elements

TODO: Move to Element.

Most of the basic elements will allow you to manipulate their content, HTML attributes or even add custom styles:

$view->setStyle('align', 'right');
$view->setAttr('href', 'https://...');

Rest of yet-to-document/implement methods and properties

property Atk4\Ui\View::$content

Set static contents of this view.

  • $properties

Atk4\Ui\View::setProperty($key, $val)
  • $key

  • $val

Atk4\Ui\View::set($arg1 = [], $arg2 = null)
  • $arg1

  • $arg2