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POHow to detect a 'flick' after drag?
 

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  1. POHow to detect a 'flick' after drag?
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    <p>I'm trying to implement a simple custom scrolling method in my mobile web app. I'm having trouble with the vertical scrolling where I'd like to have a little momentum effect if the page is 'flicked'. </p> <p>The problem is detecting a "flick" gesture, (the velocity and perhaps length of that gesture) after a dragging gesture, changing direction and what not. Hope you understand what I mean, you can drag the page up or down and at the end of that drag, I'd like to detect if there is also a flick.. </p> <p>How do you separate the two? How does such a logic look? </p> <p>Many thanks for any help.</p> <p>The code: (sorry if this excerpt is a bit of a mess)</p> <pre><code> var Device = function() { //define some private variablees var startY, startX, startTime, deltaY = 0, deltaX = 0, lastY, currentPage, nextPage, prevPage, directionY, lastTime, pages, pane, offsetX = 0, offsetY = 0, isPanning, isScrolling, isTouch = "ontouchstart" in window; return { init: function() { document.getElementById('frame').addEventListener(isTouch ? 'touchstart' : 'mousedown', Device.onTouchStart, false); //get all panes in an array panes = document.querySelectorAll('.pane'); }, onTouchStart: function (evt) { //get X and Y of the touch event var touch = isTouch ? event.touches[0] : event; startY = touch.clientY; //add listener for touch move and end document.addEventListener(isTouch ? 'touchmove' : 'mousemove', Device.onTouchMove, false); document.addEventListener(isTouch ? 'touchend' : 'mouseup', Device.onTouchEnd, false); startTime = new Date(); }, onTouchMove: function (evt) { //get X and Y of the touch event var touch = isTouch ? event.touches[0] : event; currentY = touch.clientY; //calc touch length deltaY = currentY - startY; //Detect if scroll is bigger than threshold 5px if (Math.abs(deltaY) &gt; 5 &amp;&amp; !isPanning) { isScrolling = true; //get the element pane = panes[0]; //set new position offsetY = pane.lastOffset + deltaY; //call animation Device.scrollTo(pane,0,offsetY); } //detect last direction directionY = (lastY &gt;= currentY) ? 1 : 0; //roll over last variables lastY = currentY; lastTime = new Date(); }, onTouchEnd: function () { //timing var endTime = new Date(); var velocity = (endTime - lastTime).toFixed(0); console.log('velocity: ' + velocity); //TEMPORARY pane.lastOffset = offsetY; isScrolling = false; //housekeeping document.removeEventListener(isTouch ? 'touchmove' : 'mousemove', Device.onTouchMove, false); document.removeEventListener(isTouch ? 'touchend' : 'mouseup', Device.onTouchEnd, false); //call for momentum Device.doMomentum(velocity); }, scrollTo: function(el,x,y) { if (el) { el.style['-webkit-transition-timing-function'] = ''; el.style['-webkit-transition-duration'] = '0ms'; el.style[ 'WebkitTransform' ] = 'translate3d('+x+'px,'+y+'px, 0px)'; } }, animateTo: function(el,x,y) { if (el) { el.style['-webkit-transition-timing-function'] = 'cubic-bezier(0,0,0.25,1)'; el.style['-webkit-transition-duration'] = '300ms'; el.style[ 'WebkitTransform' ] = 'translate3d('+x+'px,'+y+'px, 0px)'; } }, doMomentum: function(velocity) { console.log((directionY == 1) ? 'up': 'down'); console.log('pane.lastOffset: ' + pane.lastOffset); var endPosition; if (directionY == 1) { endPosition = pane.lastOffset - velocity; } else { endPosition = parseFloat(pane.lastOffset) + parseFloat(velocity); } console.log(endPosition); Device.animateTo(pane,0,endPosition); pane.lastOffset = endPosition; } </code></pre>
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