+ This example shows how you can support a "swipeleft" gesture, built on + top of the synthetic "gesturemove" events, which work not only on touch + devices, but also on mouse based input devices. +
+Modules Used
+ +For the example, the two core modules we'll use are:
+ +-
+
- The
event-movemodule
+ -
+ Provides the
gesturemovestart,gesturemoveandgesturemoveend+ low-level gesture events. These events are fired whenever the user + performs a move gesture (mouse button/finger down, mouse/finger move, + mouse button/finger up) with the mouse or their finger. +
+ - The
transitionsmodule
+ - + Provides transitions support, leveraging CSS transitions under the hood + where supported. + +
The YUI use statement for the example is shown below:
+ +YUI().use("node-base", "node-event-delegate", "transition", "event-move", function(Y) {
+ ...
+});
+
+
+Delegating Gesture Move Events
+ +
+ The basic idea for the example is to listen for a gesturemovestart on a
+ list item, and when we get one, store its position, and then listen for a
+ gesturemoveend. If the gesturemoveend occurs more than X pixels to the left
+ of the start, then we've identified a "swipeleft" gesture. Future versions
+ of the library will package such logic into a higher level gesture event
+ (ala event-flick).
+
+ For this example, since we're dealing with a list of items, rather than
+ attach individual listeners to each <li> in the list, we use
+ delegate on the parent <ul> element, which leads to better
+ performance and avoids having to add/remove listeners each time the
+ contents of the list change. The gesturemovestart, gesturemove and
+ gesturemoveend are synthetic events, and can all be used with delegate,
+ just like any DOM event.
+
+ We set up a delegate listener on the <ul> which listens for the
+ gesturemovestart event (gesturemovestart abstracts
+ mousedown/touchstart events under the hood). The delegate listener is
+ set up to be notified when the target of the gesturemovestart is an
+ <li>
+
Y.Node.one("#swipe").delegate("gesturemovestart", function(e) {
+
+ ...
+
+}, "li", { // filter for "li"
+ preventDefault:true
+});
+
+
+
+ The gesturemovestart event supports a configuration object passed as an
+ additional subscription argument, which can be used to set minimum distance
+ and minimum time thresholds at which to fire the start event. The
+ configuration also supports the ability to prevent the default behavior
+ before the minimum time or distance thresholds kick in, which is what we do
+ above by passing preventDefault:true.
+
+ The advantage of the gesture synthetic events is that the developer can use + the same API without having to worry about whether or not the browser + platform is touch based or mouse based. +
+ +Gesture Move End
+ +
+ As mentioned above, the gesturemovestart listener is notified whenever a
+ mousedown or touchstart is received on a list item. The listener has
+ access to:
+
-
+
e.currentTarget
+ - The list item targeted. +
e.target
+ - + The element clicked on (it may be an element inside the targeted + list item, the span for example). + +
e.container
+ - + The element to which the delegate listener is attached (the ul in + this case). + +
+ The event facade also has the page coordinates for the mousedown or
+ touchstart event. We use the list item's setData method, to store the
+ pageX position for the start event, so we can compare it when we get the
+ gesturemoveend event. This way it's stored on the node instance, and we
+ don't need to pass it along separately to the gesturemoveend event, or
+ store it globally.
+
+ getData, setData and clearData are useful methods to store ad-hoc
+ node centric data.
+
Y.Node.one("#swipe").delegate("gesturemovestart", function(e) {
+
+ var item = e.currentTarget,
+ target = e.target,
+ container = e.container,
+
+ ...
+
+ item.setData("swipeStart", e.pageX);
+
+ item.once("gesturemoveend", function(e) {
+
+ var swipeStart = item.getData("swipeStart"),
+ swipeEnd = e.pageX,
+ isSwipeLeft = (swipeStart - swipeEnd) > MIN_SWIPE;
+
+ if (isSwipeLeft) {
+ item.one(".myapp-delete").removeClass("myapp-hidden");
+ }
+
+ });
+
+ ...
+
+});
+
+
+
+ When we get the gesturemovestart event, we set up a listener for the
+ gesturemoveend event, so we can determine the end of the gesture, and
+ figure out if the user swiped left. Since we don't want to set up a new
+ listener every time we get a gesturemovestart we use once to set up the
+ gesturemoveend listener. once will detach the listener after it's been
+ invoked. Again, since gesturemoveend is a synthetic event, it works with
+ once just like any other DOM event.
+
+ In the gesturemoveend listener we check the page position of the event,
+ and if it's far enough to the left of the start position, we display the
+ "Delete" button by removing the hidden class which it contains.
+
Transitions
+ +
+ To hide and remove the item when the delete button is pressed, we use the
+ transition method, to animate its opacity and height down to 0. Under the
+ hood transition will use CSS transition support where available (WebKit)
+ and set up timer based animation where not (IE). As with the gesture event
+ support, the developer gets to use the same API without having to worry
+ about the browser environment.
+
item = target.get("parentNode");
+
+item.transition({
+ duration:0.3,
+ opacity:0,
+ height:0
+}, function() {
+ this.remove();
+});
+
+
++ The second argument to transition above is a callback function, which is + invoked when the transition is complete. We use this support to remove the + item from the DOM. +
+ +Full Code Listing
+ +YUI().use('node-base','node-event-delegate', 'transition', 'event-move', function (Y) {
+
+ var MIN_SWIPE = 10;
+
+ Y.all(".myexample-hidden").removeClass("myexample-hidden");
+
+ Y.one("#swipe").delegate("gesturemovestart", function(e) {
+
+ var item = e.currentTarget,
+ target = e.target,
+ container = e.container,
+ isDeleteButton = target.hasClass("myapp-delete");
+
+ // Prevent Text Selection in IE
+ item.once("selectstart", function(e) {
+ e.preventDefault();
+ });
+
+ if (!isDeleteButton) {
+
+ container.all(".myapp-delete").addClass("myapp-hidden");
+
+ item.setData("swipeStart", e.pageX);
+
+ item.once("gesturemoveend", function(e) {
+
+ var swipeStart = item.getData("swipeStart"),
+ swipeEnd = e.pageX,
+ isSwipeLeft = (swipeStart - swipeEnd) > MIN_SWIPE;
+
+ if (isSwipeLeft) {
+ item.one(".myapp-delete").removeClass("myapp-hidden");
+ }
+
+ });
+ } else {
+ item = target.get("parentNode");
+
+ if (item.get("id") != "kitkat" || confirm("Seriously? The KitKats?")) {
+ item.transition({
+ duration:0.3,
+ opacity:0,
+ height:0
+ }, function() {
+ this.remove();
+ });
+ }
+ }
+
+ }, "li", {
+ preventDefault:true
+ });
+});
+
+