javascript scroll event for iPhone/iPad?

问题

I can't seem to capture the scroll event on an iPad. None of these work, what I am doing wrong?

window.onscroll=myFunction;

document.onscroll=myFunction;

window.attachEvent("scroll",myFunction,false);

document.attachEvent("scroll",myFunction,false);

They all work even on Safari 3 on Windows. Ironically, EVERY browser on the PC supports window.onload= if you don't mind clobbering existing events. But no go on iPad.

回答1:

The iPhoneOS does capture onscroll events, except not the way you may expect.

One-finger panning doesn’t generate any events until the user stops panning—an onscroll event is generated when the page stops moving and redraws—as shown in Figure 6-1.

Similarly, scroll with 2 fingers fires onscroll only after you've stopped scrolling.

The usual way of installing the handler works e.g.

window.addEventListener('scroll', function() { alert("Scrolled"); });
// or
$(window).scroll(function() { alert("Scrolled"); });
// or
window.onscroll = function() { alert("Scrolled"); };
// etc

(See also https://developer.apple.com/library/content/documentation/AppleApplications/Reference/SafariWebContent/HandlingEvents/HandlingEvents.html)

回答2:

For iOS you need to use the touchmove event as well as the scroll event like this:

document.addEventListener("touchmove", ScrollStart, false);
document.addEventListener("scroll", Scroll, false);

function ScrollStart() {
    //start of scroll event for iOS
}

function Scroll() {
    //end of scroll event for iOS
    //and
    //start/end of scroll event for other browsers
}

回答3:

Sorry for adding another answer to an old post but I usually get a scroll event very well by using this code (it works at least on 6.1)

element.addEventListener('scroll', function() {
    console.log(this.scrollTop);
});

// This is the magic, this gives me "live" scroll events
element.addEventListener('gesturechange', function() {});

And that works for me. Only thing it doesn't do is give a scroll event for the deceleration of the scroll (Once the deceleration is complete you get a final scroll event, do as you will with it.) but if you disable inertia with css by doing this

-webkit-overflow-scrolling: none;

You don't get inertia on your elements, for the body though you might have to do the classic

document.addEventListener('touchmove', function(e) {e.preventDefault();}, true);

回答4:

I was able to get a great solution to this problem with iScroll, with the feel of momentum scrolling and everything https://github.com/cubiq/iscroll The github doc is great, and I mostly followed it. Here's the details of my implementation.

HTML: I wrapped the scrollable area of my content in some divs that iScroll can use:

<div id="wrapper">
  <div id="scroller">
    ... my scrollable content
  </div>
</div>

CSS: I used the Modernizr class for "touch" to target my style changes only to touch devices (because I only instantiated iScroll on touch).

.touch #wrapper {
  position: absolute;
  z-index: 1;
  top: 0;
  bottom: 0;
  left: 0;
  right: 0;
  overflow: hidden;
}
.touch #scroller {
  position: absolute;
  z-index: 1;
  width: 100%;
}

JS: I included iscroll-probe.js from the iScroll download, and then initialized the scroller as below, where updatePosition is my function that reacts to the new scroll position.

# coffeescript
if Modernizr.touch
  myScroller = new IScroll('#wrapper', probeType: 3)
  myScroller.on 'scroll', updatePosition
  myScroller.on 'scrollEnd', updatePosition

You have to use myScroller to get the current position now, instead of looking at the scroll offset. Here is a function taken from http://markdalgleish.com/presentations/embracingtouch/ (a super helpful article, but a little out of date now)

function getScroll(elem, iscroll) {   
  var x, y;

  if (Modernizr.touch && iscroll) {
    x = iscroll.x * -1;
    y = iscroll.y * -1;   
  } else {
    x = elem.scrollTop;
    y = elem.scrollLeft;   
  }

  return {x: x, y: y}; 
}

The only other gotcha was occasionally I would lose part of my page that I was trying to scroll to, and it would refuse to scroll. I had to add in some calls to myScroller.refresh() whenever I changed the contents of the #wrapper, and that solved the problem.

EDIT: Another gotcha was that iScroll eats all the "click" events. I turned on the option to have iScroll emit a "tap" event and handled those instead of "click" events. Thankfully I didn't need much clicking in the scroll area, so this wasn't a big deal.