JQuery Sortable and automatic scrolling

Question

I am trying to get JQuery Sortable to work but I have run into a slight usability problem.

The list that I am trying to sort is quite large (about 200 items). If the

Answer 1

Scroll window when an item is dragged close to the top or bottom.

I could not get any of the other answers working. Using Chrome and a sortable grid that needs to scroll vertically when an item is being dragged to the top or bottom edge of the window.

NOTE: This only works for scrolling the entire window. This will not work if you have a scrollable section inside of the window and need to scroll that.

I was able to get the following working flawlessly:

var currentlyScrolling = false;

var SCROLL_AREA_HEIGHT = 40; // Distance from window's top and bottom edge.

$(".sortable").sortable({
    scroll: true,

    sort: function(event, ui) {

      if (currentlyScrolling) {
        return;
      }

      var windowHeight   = $(window).height();
      var mouseYPosition = event.clientY;

      if (mouseYPosition < SCROLL_AREA_HEIGHT) {
        currentlyScrolling = true;

        $('html, body').animate({
          scrollTop: "-=" + windowHeight / 2 + "px" // Scroll up half of window height.
        }, 
        400, // 400ms animation.
        function() {
          currentlyScrolling = false;
        });

      } else if (mouseYPosition > (windowHeight - SCROLL_AREA_HEIGHT)) {

        currentlyScrolling = true;

        $('html, body').animate({
          scrollTop: "+=" + windowHeight / 2 + "px" // Scroll down half of window height.
        }, 
        400, // 400ms animation.
        function() {
          currentlyScrolling = false;
        });

      }
    }
});

Coffeescript Version

currentlyScrolling = false
SCROLL_AREA_HEIGHT = 40

sort: (event, ui) ->

  return if currentlyScrolling

  windowHeight = $( window ).height()

  mouseYPosition = event.clientY

  if mouseYPosition < SCROLL_AREA_HEIGHT # Scroll up.
    currentlyScrolling = true
    $( 'html, body' ).animate( { scrollTop: "-=" + windowHeight / 2 + "px" }, 400, () -> currentlyScrolling = false )

  else if mouseYPosition > ( windowHeight - SCROLL_AREA_HEIGHT ) # Scroll down.
    currentlyScrolling = true
    $( 'html, body' ).animate( { scrollTop: "+=" + windowHeight / 2 + "px" }, 400, () -> currentlyScrolling = false )