An Ext JS application's UI is made up of one or many widgets called {@link Ext.Component Component}s. All Components are subclasses of the {@link Ext.Component} class
which allows them to participate in automated lifecycle management including instantiation, rendering, sizing and positioning, and destruction.
Ext JS provides a wide range of useful Components out of the box, and any Component can easily be extended to create a customized Component.
A {@link Ext.container.Container Container} is a special type of Component that can contain other Components. A typical application is made up of many nested Components in a tree-like
structure that is referred to as the Component hierarchy. Containers are responsible for managing the Component lifecycle of their children, which includes creation, rendering,
sizing and positioning, and destruction. A typical application's Component hierarchy starts with a {@link Ext.container.Viewport Viewport} at the top,
which has other Containers and/or Components nested within it:
{@img component_hierarchy.png Component Hierarchy}
Child Components are added to a Container using the Container's {@link Ext.container.Container#cfg-items items} configuration property. This example uses {@link Ext#create Ext.create}
to instantiate two {@link Ext.panel.Panel Panel}s, then adds those Panels as child Components of a Viewport:
@example
var childPanel1 = Ext.create('Ext.panel.Panel', {
title: 'Child Panel 1',
html: 'A Panel'
});
var childPanel2 = Ext.create('Ext.panel.Panel', {
title: 'Child Panel 2',
html: 'Another Panel'
});
Ext.create('Ext.container.Viewport', {
items: [ childPanel1, childPanel2 ]
});
Containers use {@link Ext.layout.container.Container Layout Manager}s to size and position their child Components.
For more information on Layouts and Containers please refer to the Layouts and Containers Guide.
See the Container Example for a working demo showing how to add Components to a Container using the items configuration.
Every Component has a symbolic name called an {@link Ext.Component#cfg-xtype xtype}. For example {@link Ext.panel.Panel} has an xtype of 'panel'.
The xtypes for all Components are listed in the {@link Ext.Component API Docs for Component}.
The above example showed how to add already instantiated {@link Ext.Component Component}s to a {@link Ext.container.Container Container}.
In a large application, however, this is not ideal since not all of the Components need to be instantiated right away,
and some Components might never be instantiated depending on how the application is used. For example an application that uses a {@link Ext.tab.Panel Tab Panel}
will only need the contents of each tab to be rendered if and when each tab is clicked on by the user. This is where xtypes come in handy
by allowing a Container's children to be configured up front, but not instantiated until the Container determines it is necessary.
The following example code demonstrates lazy instantiation and rendering of a Container's Child components using a Tab Panel.
Each tab has an event listener that displays an alert when the tab is rendered.
Ext.create('Ext.tab.Panel', {
renderTo: Ext.getBody(),
height: 100,
width: 200,
items: [
{
// Explicitly define the xtype of this Component configuration.
// This tells the Container (the tab panel in this case)
// to instantiate a Ext.panel.Panel when it deems necessary
xtype: 'panel',
title: 'Tab One',
html: 'The first tab',
listeners: {
render: function() {
Ext.MessageBox.alert('Rendered One', 'Tab One was rendered.');
}
}
},
{
// this component configuration does not have an xtype since 'panel' is the default
// xtype for all Component configurations in a Container
title: 'Tab Two',
html: 'The second tab',
listeners: {
render: function() {
Ext.MessageBox.alert('Rendered One', 'Tab Two was rendered.');
}
}
}
]
});
Running this code results in an immediate alert for the first tab. This happens because it is the default active tab,
and so its Container Tab Panel instantiates and renders it immediately.
{@img lazy_render1.png Lazy Render 1}
The alert for the second tab does not get displayed until the tab is clicked on. This shows that the tab was not rendered until
needed, since the {@link Ext.Component#event-render render} event did not fire until the tab was activated.
{@img lazy_render2.png Lazy Render 2}
For a working demo see the Lazy Instantiation Example
All {@link Ext.Component Component}s have built in {@link Ext.Component#method-show show} and {@link Ext.Component#method-hide hide} methods.
The default CSS method used to hide the Component is "display: none", but this can be changed using the {@link Ext.Component#cfg-hideMode hideMode} configuration:
var panel = Ext.create('Ext.panel.Panel', {
renderTo: Ext.getBody(),
title: 'Test',
html: 'Test Panel',
hideMode: 'visibility' // use the CSS visibility property to show and hide this component
});
panel.hide(); // hide the component
panel.show(); // show the component
Floating {@link Ext.Component Component} are positioned outside of the document flow using CSS absolute positioning, and do not participate in their Containers' layout.
Some Components such as {@link Ext.window.Window Window}s are floating by default, but any Component can be made floating using the {@link Ext.Component#cfg-floating floating} configuration.
var panel = Ext.create('Ext.panel.Panel', {
width: 200,
height: 100,
floating: true, // make this panel an absolutely-positioned floating component
title: 'Test',
html: 'Test Panel'
});
The above code instantiates a {@link Ext.panel.Panel Panel} but does not render it. Normally a Component either has a {@link Ext.Component#cfg-renderTo renderTo}
configuration specified, or is added as a child Component of a {@link Ext.container.Container Container}, but in the case of floating Components neither of these is needed.
Floating Components are automatically rendered to the document body the first time their {@link Ext.Component#method-show show} method is called:
panel.show(); // render and show the floating panel
Here are a few other configurations and methods to make note of related to floating components:
{@link Ext.Component#cfg-draggable draggable} - enables dragging of a floating Component around the screen.{@link Ext.Component#cfg-shadow shadow} - customizes the look of a floating Component's shadow.{@link Ext.Component#method-alignTo alignTo()} - aligns a floating Component to a specific element.{@link Ext.Component#method-center center()} - centers a floating Component in its Container.For a working demo of floating Component features see the Floating Panel Example.
When creating a new UI class, the decision must be made whether that class should own an instance of a {@link Ext.Component Component}, or to extend that Component.
It is recommended to extend the nearest base class to the functionality required. This is because of the automated lifecycle management Ext JS provides which
includes automated rendering when needed, automatic sizing and positioning of Components when managed by an appropriate layout manager,
and automated destruction on removal from a {@link Ext.Container Container}.
It is easier to write a new class which is a Component and can take its place in the Component hierarchy rather than a new class which has an Ext JS Component,
and then has to render and manage it from outside.
The {@link Ext.Class Class System} makes it easy to extend existing Components. The following example creates a subclass of {@link Ext.Component} without
adding any additional functionality:
Ext.define('My.custom.Component', {
extend: 'Ext.Component'
});
Ext JS uses the Template method pattern to delegate to subclasses, behavior which is specific only to that subclass.
The meaning of this is that each class in the inheritance chain may "contribute" an extra piece of logic to certain phases in the Component's lifecycle.
Each class implements its own special behavior while allowing the other classes in the inheritance chain to continue to contribute their own logic.
An example is the render function. render is a private method defined in {@link Ext.Component Component}'s superclass,
{@link Ext.AbstractComponent AbstractComponent} that is responsible for initiating the rendering phase of the Component lifecycle.render must not be overridden, but it calls onRender during processing to allow the subclass implementor to add an onRender
method to perform class-specific processing. Every onRender method must call its superclass' onRender method before "contributing" its extra logic.
The diagram below illustrates the functioning of the onRender template method.
The render method is called (This is done by a Container’s layout manager). This method may not be overridden and is implemented by the Ext base class.
It calls this.onRender which is the implementation within the current subclass (if implemented).
This calls the superclass version which calls its superclass version etc. Eventually, each class has contributed its functionality, and control returns to the render function.
{@img template_pattern.png Template Pattern}
Here is an example of a Component subclass that implements the onRender method:
Ext.define('My.custom.Component', {
extend: 'Ext.Component',
onRender: function() {
this.callParent(arguments); // call the superclass onRender method
// perform additional rendering tasks here.
}
});
It is important to note that many of the template methods also have a corresponding event. For example the {@link Ext.Component#event-render render}
event is fired after the Component is rendered. When subclassing, however, it is it is essential to use template methods to perform class logic at
important phases in the lifecycle and not events. Events may be programmatically suspended, or may be stopped by a handler.
Below are the template methods that can be implemented by subclasses of Component:
initComponentbeforeShowonShowafterShowonShowCompleteafterShow method is completeonHideafterHideonRenderafterRenderonEnableonDisableonAddedonRemovedonResizeonPositiononDestroybeforeDestroyafterSetPositionafterComponentLayoutbeforeComponentLayoutChoosing the best class to extend is mainly a matter of efficiency, and which capabilities the base class must provide.
There has been a tendency to always extend {@link Ext.Panel} whenever any set of UI Components needs to be rendered and managed.
The Panel class has many capabilities:
If these are not needed, then using a Panel is a waste of resources.
If the required UI Component does not need to contain any other Components, that is, if it just to encapsulate some form of HTML which performs the requirements,
then extending {@link Ext.Component} is appropriate. For example, the following class is a Component that wraps an HTML image element, and allows setting
and getting of the image's src attribute. It also fires a load event when the image is loaded:
Ext.define('Ext.ux.Image', {
extend: 'Ext.Component', // subclass Ext.Component
alias: 'widget.managedimage', // this component will have an xtype of 'managedimage'
autoEl: {
tag: 'img',
src: Ext.BLANK_IMAGE_URL,
cls: 'my-managed-image'
},
// Add custom processing to the onRender phase.
// Add a ‘load’ listener to the element.
onRender: function() {
this.autoEl = Ext.apply({}, this.initialConfig, this.autoEl);
this.callParent(arguments);
this.el.on('load', this.onLoad, this);
},
onLoad: function() {
this.fireEvent('load', this);
},
setSrc: function(src) {
if (this.rendered) {
this.el.dom.src = src;
} else {
this.src = src;
}
},
getSrc: function(src) {
return this.el.dom.src || this.src;
}
});
Usage:
var image = Ext.create('Ext.ux.Image');
Ext.create('Ext.panel.Panel', {
title: 'Image Panel',
height: 200,
renderTo: Ext.getBody(),
items: [ image ]
});
image.on('load', function() {
console.log('image loaded: ', image.getSrc());
});
image.setSrc('http://www.sencha.com/img/sencha-large.png');
See the Managed Image Example for a working demo. This example is for demonstration purposes only -
the {@link Ext.Img} class should be used for managing images in a real world application.
If the required UI Component is to contain other Components, but does not need any of the previously mentioned additional capabilities of a {@link Ext.Panel Panel},
then {@link Ext.container.Container} is the appropriate class to extend. At the Container level, it is important to remember which {@link Ext.layout.container.Container Layout}
is to be used to render and manage child Components.
Containers have the following additional template methods:
onBeforeAddonAddonRemovebeforeLayoutafterLayoutIf the required UI Component must have a header, footer, or toolbars, then Ext.Panel is the appropriate class to extend.
Important: A Panel is a Container. It is important to remember which {@link Ext.layout.container.Container Layout} is to be used to render and manage child Components.
Classes which extend Ext.Panel are usually highly application-specific and are generally used to aggregate other UI Components
(Usually Containers, or form Fields) in a configured layout, and provide means to operate on the contained Components by means
of controls in the {@link Ext.panel.Panel#cfg-tbar tbar} and the {@link Ext.panel.Panel#cfg-bbar bbar}.
Panels have the following additional template methods:
afterCollapseafterExpandonDockedAddonDockedRemove