Spry

Work with observer notifications

    Observer notifications overview

    The XML data set supports an observer mechanism that allows an object or callback function to receive event notifications.

    Notification

    Description

    onPreLoad

    The data set is about to send a request for data. If the data set depends on other data sets, this event notification will not send until they are all loaded successfully.

    onPostLoad

    The request for data was successful. The data is accessible.

    onLoadError

    An error occurred while requesting the data.

    onDataChanged

    The data in the data set has been modified.

    onPreSort

    The data in the data set is about to be sorted.

    onPostSort

    The data in the data set has been sorted.

    onCurrentRowChanged

    The data set's notion of the current row has changed.

    Objects as observers

    To receive notifications, an object must define a method for each notification it is interested in receiving, and then register itself as an observer on the data set. For example, an object interested in onDataChanged notifications must define an onDataChanged() method and then call addObserver().

    var dsPhotos = new Spry.Data.XMLDataSet("/photos.php?galleryid=2000", "/gallery/photos/photo");
...
var myObserver = new Object;
myObserver.onDataChanged = function(dataSet, data)
{
	alert("onDataChanged called!");
};
dsPhotos.addObserver(myObserver);

    The first argument for each notification method is the object that is sending the notification. For data set observers, this is always the data set object. The second argument is either undefined, or an object that depends on the type of notification.

    Notification

    Data passed into notification

    onPreLoad

    undefined

    onPostLoad

    undefined

    onLoadError

    The Spry.Utils.loadURL.Request object that was used when making the request

    onDataChanged

    undefined

    onPreSort

    Object with the following properties:

    oldSortColumns: An array of columns used during the last sort.

    oldSortOrder: The sort order used during the last sort.

    newSortColumns: The array of columns about to be used for the sort.

    newSortOrder: The sort order about to be used for the sort.

    onPostSort

    Object with the following properties:

    oldSortColumns: An array of the columns used in the previous sort.

    oldSortOrder: The sort order used during the previous sort.

    newSortColumns: The array of columns used for the sort.

    newSortOrder: The sort order used for the sort.

    onCurrentRowChanged

    Object with the following properties:

    oldRowID: The ds_RowID of the last current row.

    newRowID: The ds_RowID of the current row.

    To stop an object from receiving notifications, the object must be removed from the list of observers with a call to removeObserver().

    var dsPhotos = new Spry.Data.XMLDataSet("/photos.php?galleryid=2000", "/gallery/photos/photo");
...
dsPhotos.removeObserver(myObserver);

    Functions as observers

    Functions can also be registered as observers. The main difference between object and function observers is that an object is only notified for the notification methods it defines, whereas a function observer is called for every type of event notification.

    var dsPhotos = new Spry.Data.XMLDataSet("/photos.php?galleryid=2000", "/gallery/photos/photo");
...
function myObserverFunc(notificationType, dataSet, data)
{
	if (notificationType == "onDataChanged")
		alert("onDataChanged called!";
	else if (notificationType == "onPostSort")
		alert("onPostSort called!";
};
dsPhotos.addObserver(myObserverFunc);

    A function observer is registered with the same call to addObserver.

    When the function is called, the first argument to be passed into it is the notification type. This is a string that is the name of the notification. The second argument is the notifier, which in this case is the data set, and the third argument is the data for the notification.

    To stop a function observer from receiving notifications, it must be removed from the list of observers with a call to removeObserver().

    var dsPhotos = new Spry.Data.XMLDataSet("/photos.php?galleryid=2000", "/gallery/photos/photo");
...
dsPhotos.removeObserver(myObserverFunc);