com.vaadin.client.ui

Class TouchScrollDelegate

java.lang.Object

com.vaadin.client.ui.TouchScrollDelegate

All Implemented Interfaces:

com.google.gwt.event.shared.EventHandler, com.google.gwt.user.client.Event.NativePreviewHandler

public class TouchScrollDelegate
extends Object
implements com.google.gwt.user.client.Event.NativePreviewHandler

Provides one finger touch scrolling for elements with once scrollable elements inside. One widget can have several of these scrollable elements. Scrollable elements are provided in the constructor. Users must pass touchStart events to this delegate, from there on the delegate takes over with an event preview. Other touch events needs to be sunken though.

This is bit similar as Scroller class in GWT expenses example, but ideas drawn from iscroll.js project:

• uses GWT event mechanism.
• uses modern CSS trick during scrolling for smoother experience: translate3d and transitions

Scroll event should only happen when the "touch scrolling actually ends". Later we might also tune this so that a scroll event happens if user stalls her finger long enought. TODO static getter for active touch scroll delegate. Components might need to prevent scrolling in some cases. Consider Table with drag and drop, or drag and drop in scrollable area. Optimal implementation might be to start the drag and drop only if user keeps finger down for a moment, otherwise do the scroll. In this case, the draggable component would need to cancel scrolling in a timer after touchstart event and take over from there. TODO support scrolling horizontally TODO cancel if user add second finger to the screen (user expects a gesture). TODO "scrollbars", see e.g. iscroll.js TODO write an email to sjobs ?§t apple dot com and beg for this feature to be built into webkit. Seriously, we should try to lobbying this to webkit folks. This sure ain't our business to implement this with javascript. TODO collect all general touch related constant to better place.

Author:

Matti Tahvonen, Vaadin Ltd

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static class	TouchScrollDelegate.TouchScrollHandler A helper class for making a widget scrollable.

Field Summary

Fields

Modifier and Type	Field and Description
static int	SIGNIFICANT_MOVE_THRESHOLD

Constructor Summary

Constructors

Constructor and Description
TouchScrollDelegate(com.google.gwt.dom.client.Element... elements)

Method Summary

Modifier and Type	Method and Description
static TouchScrollDelegate.TouchScrollHandler	enableTouchScrolling(com.google.gwt.user.client.ui.Widget widget, com.google.gwt.dom.client.Element... scrollables) Makes the given elements scrollable, either natively or by using a TouchScrollDelegate, depending on platform capabilities.
static TouchScrollDelegate	getActiveScrollDelegate()
static ArrayList<com.google.gwt.dom.client.Element>	getElements(com.google.gwt.dom.client.Element scrolledElement2)
static double	getTimeStamp() Long calculation are not very efficient in GWT, so this helper method returns timestamp in double.
boolean	isMoved() Has user moved the touch.
void	onPreviewNativeEvent(com.google.gwt.user.client.Event.NativePreviewEvent event)
void	onTouchStart(com.google.gwt.event.dom.client.TouchStartEvent event)
void	setElements(com.google.gwt.dom.client.Element[] elements)
void	setScrollHandler(com.google.gwt.event.dom.client.ScrollHandler scrollHandler)
void	stopScrolling() Forces the scroll delegate to cancels scrolling process.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

SIGNIFICANT_MOVE_THRESHOLD

public static final int SIGNIFICANT_MOVE_THRESHOLD

See Also:

Constant Field Values

Constructor Detail

TouchScrollDelegate

public TouchScrollDelegate(com.google.gwt.dom.client.Element... elements)

Method Detail

enableTouchScrolling

public static TouchScrollDelegate.TouchScrollHandler enableTouchScrolling(com.google.gwt.user.client.ui.Widget widget,
                                                                          com.google.gwt.dom.client.Element... scrollables)

Makes the given elements scrollable, either natively or by using a TouchScrollDelegate, depending on platform capabilities.

Parameters:

widget - The widget that contains scrollable elements

scrollables - The elements inside the widget that should be scrollable

Returns:

A scroll handler for the given widget.

setScrollHandler

public void setScrollHandler(com.google.gwt.event.dom.client.ScrollHandler scrollHandler)

getActiveScrollDelegate

public static TouchScrollDelegate getActiveScrollDelegate()

isMoved

public boolean isMoved()

Has user moved the touch.

Returns:

stopScrolling

public void stopScrolling()

Forces the scroll delegate to cancels scrolling process. Can be called by users if they e.g. decide to handle touch event by themselves after all (e.g. a pause after touch start before moving touch -> interpreted as long touch/click or drag start).

onTouchStart

public void onTouchStart(com.google.gwt.event.dom.client.TouchStartEvent event)

getElements

public static ArrayList<com.google.gwt.dom.client.Element> getElements(com.google.gwt.dom.client.Element scrolledElement2)

onPreviewNativeEvent

public void onPreviewNativeEvent(com.google.gwt.user.client.Event.NativePreviewEvent event)

Specified by:

onPreviewNativeEvent in interface com.google.gwt.user.client.Event.NativePreviewHandler

setElements

public void setElements(com.google.gwt.dom.client.Element[] elements)

getTimeStamp

public static double getTimeStamp()

Long calculation are not very efficient in GWT, so this helper method returns timestamp in double.

Returns: