Implementing a Fixed Position iOS Web Application

Tue, 25 Nov 2014 02:42:19 +0000

Scroller = function(element) {
  this.element = this;
  this.startTouchY = 0;
  this.animateTo(0);

  element.addEventListener(‘touchstart’, this, false);
  element.addEventListener(‘touchmove’, this, false);
  element.addEventListener(‘touchend’, this, false);
}

Scroller.prototype.handleEvent = function(e) {
  switch (e.type) {
    case “touchstart”:
      this.onTouchStart(e);
      break;
    case “touchmove”:
      this.onTouchMove(e);
      break;
    case “touchend”:
      this.onTouchEnd(e);
      break;
  }
}

Scroller.prototype.onTouchStart = function(e) {
  // This will be shown in part 4.
  this.stopMomentum();

  this.startTouchY = e.touches[0].clientY;
  this.contentStartOffsetY = this.contentOffsetY;
}

Scroller.prototype.onTouchMove = function(e) {
  if (this.isDragging()) {
    var currentY = e.touches[0].clientY;
    var deltaY = currentY - this.startTouchY;
    var newY = deltaY + this.contentStartOffsetY;
    this.animateTo(newY);
  }
}

Scroller.prototype.onTouchEnd = function(e) {
  if (this.isDragging()) {
    if (this.shouldStartMomentum()) {
      // This will be shown in part 3.
      this.doMomentum();
    } else {
      this.snapToBounds();
    }
  }
}

Scroller.prototype.animateTo = function(offsetY) {
  this.contentOffsetY = offsetY;

  // We use webkit-transforms with translate3d because these animations
  // will be hardware accelerated, and therefore significantly faster
  // than changing the top value.
  this.element.style.webkitTransform = ‘translate3d(0, ‘ + offsetY + ‘px, 0)’;
}

// Implementation of this method is left as an exercise for the reader.
// You need to measure the current position of the scrollable content
// relative to the frame. If the content is outside of the boundaries
// then simply reposition it to be just within the appropriate boundary.
Scroller.prototype.snapToBounds = function() {
  ...
}

// Implementation of this method is left as an exercise for the reader.
// You need to consider whether their touch has moved past a certain
// threshold that should be considered ‘dragging’.
Scroller.prototype.isDragging = function() {
  ...
}

// Implementation of this method is left as an exercise for the reader.
// You need to consider the end velocity of the drag was past the
// threshold required to initiate momentum.
Scroller.prototype.shouldStartMomentum = function() {
  ...
}

Hide the address bar in a fullscreen iPhone or Android web app

Wed, 12 Nov 2014 04:34:24 +0000

var page = document.getElementById('page'),
    ua = navigator.userAgent,
    iphone = ~ua.indexOf('iPhone') || ~ua.indexOf('iPod'),
    ipad = ~ua.indexOf('iPad'),
    ios = iphone || ipad,
    // Detect if this is running as a fullscreen app from the homescreen
    fullscreen = window.navigator.standalone,
    android = ~ua.indexOf('Android'),
    lastWidth = 0;
 
if (android) {
  // Android's browser adds the scroll position to the innerHeight, just to
  // make this really fucking difficult. Thus, once we are scrolled, the
  // page height value needs to be corrected in case the page is loaded
  // when already scrolled down. The pageYOffset is of no use, since it always
  // returns 0 while the address bar is displayed.
  window.onscroll = function() {
    page.style.height = window.innerHeight + 'px'
  }
}
var setupScroll = function() {
  // Start out by adding the height of the location bar to the width, so that
  // we can scroll past it
  if (ios) {
    // iOS reliably returns the innerWindow size for documentElement.clientHeight
    // but window.innerHeight is sometimes the wrong value after rotating
    // the orientation
    var height = document.documentElement.clientHeight;
    // Only add extra padding to the height on iphone / ipod, since the ipad
    // browser doesn't scroll off the location bar.
    if (iphone && !fullscreen) height += 60;
    page.style.height = height + 'px';
  } else if (android) {
    // The stock Android browser has a location bar height of 56 pixels, but
    // this very likely could be broken in other Android browsers.
    page.style.height = (window.innerHeight + 56) + 'px'
  }
  // Scroll after a timeout, since iOS will scroll to the top of the page
  // after it fires the onload event
  setTimeout(scrollTo, 0, 0, 1);
};
(window.onresize = function() {
  var pageWidth = page.offsetWidth;
  // Android doesn't support orientation change, so check for when the width
  // changes to figure out when the orientation changes
  if (lastWidth == pageWidth) return;
  lastWidth = pageWidth;
  setupScroll();
})();

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Implementing a Fixed Position iOS Web Application

Hide the address bar in a fullscreen iPhone or Android web app