YUI Library Examples: Carousel Control: Using Ajax for deferred loading of items

Making the Carousel Widget dynamically load images on the fly

Here we will use the YUI Carousel Control's loadItems event to dynamically load the images on the fly.

This example has the following dependencies:

Initially we use YUI Connection Manager to load the initial set of items as soon as part of the DOM is visible.

We have a few simple CSS rules to set the dimensions for the Carousel items.

The YUI Carousel Control's constructor is passed numItems (the total number of items) so that it triggers the loadItems event if the items are not available. We'll use Connection Manager to load a set of items into the Carousel as early as possible.

YAHOO.util.Event.onDOMReady(function (ev) {
  var carousel, spotlight = YAHOO.util.Dom.get("spotlight");

carousel = new YAHOO.widget.Carousel("container", {
      
  /* Setting numItems is required for dynamic loading. This property lets Carousel 
     know how many total items it will ever be populated with (statically and/or dynamically).
     Not to be confused with numVisible: the number of items to display
     per page. In this example, we don't specify numVisible and Carousel 
     defaults to 3 items visible per page. */
     
     numItems: 17
  });
  YAHOO.util.Connect.asyncRequest("GET", "php/getimages.php", {
      success: function (o) {
        var i, r = eval('(' + o.responseText + ')');
        curpos = r.length;

for (i = 0; i < curpos; i++) {
          items.push(r[i]);
        }

// check if the Carousel widget is available
        if (typeof carousel != "undefined") {
          for (i = 0; i < curpos; i++) {
            // if so, shove the elements into it
            carousel.addItem(getImageTag(items[i]));
          }
          carousel.set("selectedItem", 0);
          items = [];
        }
      },

failure: function (o) {
        alert("Ajax request failed!");
      }
  });
});

The YUI Carousel Control exposes a loadItems custom event that is fired when the Carousel needs more items to be loaded. This becomes very handy for us since we can subscribe to it and add more items in to the Carousel widget when required.

In our case, the server program returns an array (JSON) of images. This is parsed in the Ajax callback and then the Carousel's addItem() is called for every image. Apart from subscribing to this event, for displaying the selected image as a spotlight, we can subscribe to the itemSelected event that Carousel control exposes. This event is triggered whenever an item is selected and it returns the index of the selected item. With the index of the item, we can use the Carousel's getElementForItem() API to get the reference to the Carousel's item (an li element in our case).

carousel.on("loadItems", function (o) {
  // more items available?
  getImages.call(this);
});

carousel.on("itemSelected", function (index) {
  var item = carousel.getElementForItem(index);

if (item) {
    spotlight.innerHTML = "<img src=http://developer.yahoo.com/ + getImage(item) + "\">";
  }
});

carousel.render();
carousel.show();

function getImageTag(img) {
    return "<img src=http://developer.yahoo.com/ + img + "\" height=\"75\" width=\"75\">";
}

The getLargeImage() function is quite easy to implement. Since we have the reference to the Carousel's item, it is straightforward to implement a function that extracts the image within it.

YUI Logger Output:

Note: Logging and debugging is currently turned off for this example.

Reload with logging
and debugging enabled.

Carousel Control Examples:

More Carousel Control Resources:

All YUI 2.x users should review the YUI 2.8.2 security bulletin, which discusses a vulnerability present in YUI 2.4.0-2.8.1.