Tablet and Touch-Screen Support in Ext JS 5

One of the most exciting additions to the Ext JS 5 feature set is support for devices with touch-screen input, including tablets and touch-screen laptops. The primary goal of this feature is to allow Ext JS applications to run on touch-screen devices with little or no modification. This means that developers can spend less time thinking about compatibility issues, and more time implementing great applications.

How Touch-Screen Support is Implemented

Support for devices with touch-screens can be broken down into three categories.

Event Normalization

Event normalization is the key to allowing Ext JS 5 applications to run on touch-screen devices. This normalization occurs behind the scenes and is a simple translation from standard mouse events to their equivalent touch and pointer events.

Pointer events are a w3c standard for dealing with events that target a specific set of coordinates on the screen, regardless of input device (mouse, touch, stylus, etc.)

When your code requests a listener for a mouse event, the framework attaches a similar touch or pointer event as needed. For example, if the application attempts to attach a mousedown listener:

myElement.on('mousedown', someFunction);

The event system translates this to touchstart in the case of a device that supports touch events:

myElement.on('touchstart', someFunction);

Or, pointerdown in the case of a device that supports pointer events:

myElement.on('pointerdown', someFunction);

This translation is in place so that you may achieve tablet and touch-screen support without any additional coding.

In most cases the framework can transition seamlessly between mouse, touch, and pointer input. However, there are a few mouse interactions (such as mouseover) that do not translate easily into touch interactions. Such events will need to be handled on an individual basis and are addressed in a following section.

Gesture System

In addition to standard DOM events, Elements also fire synthesized “gesture” events. Since the Sencha Touch event system forms the basis for the new event system in Ext JS 5, Sencha Touch users may already be familiar with this concept.

From a browser’s perspective, there are 3 primary types of pointer, touch, and mouse events - start, move, and end:

Upon interpreting the sequence and timing of these events, the framework can synthesize more complex events such as drag , swipe , longpress , pinch , rotate , and tap . Ext JS applications can listen for gesture events just like any other event, for example:

Ext.get('myElement').on('longpress', handlerFunction);

The original Sencha Touch gesture system was designed primarily with touch events in mind. By adding full support for pointer and mouse events to the Gesture system, Ext JS 5 allows any gesture to respond to any type of input. This means not only that all gestures can be triggered using touch input, but all single-point gestures (tap, swipe, etc.) can be triggered using a mouse as well. This results in a gesture system that works seamlessly across devices regardless of input type.

Touch Scroller

Native scrolling of elements with overflowing content leaves a lot to be desired in some mobile webkit browsers. The lack of momentum scrolling and scroll position indicators can make scrolling a tedious and unintuitive experience. The ‘touch scroller’, borrowed from Sencha Touch, solves this problem by implementing momentum scrolling with scroll indicators using JavaScript. Application developers typically won’t need to do anything to turn the touch scroller on. It is enabled by default in browsers where native scrolling is less than optimal.

What Touch-Screen Support Means for Applications

Normalized events and gesture recognition are active by default in Ext JS 5 applications. This means that, in most cases, no special actions are necessary to enable tablet and touch-screen support. However, there are two particular areas that may need special attention.

The first deals with mouse events that don’t have an obvious analog in the touch world. As of now, Ext JS 5 does not attempt to perform any normalization for the following mouse events:

• mouseover
• mouseout
• mousenter
• mouseleave

Application functionality that responds to these events on desktop devices may have to be re-implemented separately for touch devices. Developers should keep this in mind when architecting applications. In order to ensure that important application functionality is accessible to touch screens, it may be necessary to provide an alternate implementation for these interactions. This often means substituting the mouse event with an appropriate touch gesture. Ext JS takes this approach internally in several places.

One example is the grid component. On desktop devices, grid column header menus are shown in response to a click on the header’s trigger element. However, the trigger only becomes visible in response to a mouseover of the column header. Since a gesture equivalent to ‘mouseover’ does not exist on touch screens, the trigger never becomes visible and so cannot be touched. To ensure that the column header menu can be accessed, Ext JS displays the menu in response to a ‘longpress’ if it detects that the grid is being used on a touch-screen device.

Note: Developers of applications and custom components may need to make similar adjustments as needed.

The second area that may require attention relates to some internal framework changes. In order to support Touch gestures, Ext JS 5 switched to a delegated event model. Instead of attaching listeners directly to DOM elements, a single listener for each event type is attached at the top of the DOM (the window or document object). The Ext JS event system then dispatches event handlers based on the target elements of events that bubble up to the window object. Application developers who use only Ext JS APIs to listen for events will not experience any problems with this new approach.

However, if DOM APIs are used to directly attach listeners (addEventListener or attachEvent), or if 3rd party JavaScript libraries are used, issues may occur with the timing of directly attached event handlers relative to the timing of their delegated counterparts.

Note: Tablet and touch-screen support currently works with Safari, Chrome and IE10+. The Android browser is not currently supported.