Creating Custom Client Events
AJAX functionality in ASP.NET includes a complete multi-layered client-event model. The Sys.Application class provides events at the application level. The Sys.WebForms.PageRequestManager class provides events that pertain to parts of the page involved in partial-page rendering. Individual components, such as controls and behaviors, have their own events. For more information about these events, see Ajax Client Life-Cycle Events.
ASP.NET also enables you to add events to the client life cycle. The Sys.UI.DomEvent class enables you to bind HTML Document Object Model (DOM) events to custom ASP.NET AJAX components. In addition, the Sys.EventHandlerList class lets you create new ASP.NET AJAX client events directly.
Attaching to DOM Events
In many cases, an event you want to work with corresponds to an event defined in the HTML DOM. For example, a custom ASP.NET AJAX button control might use the click event of the HTML <button> element that it is attached to. To bind a DOM-based event to an ASP.NET AJAX application or custom component, you use the addHandler method of the DomEvent class, as shown in the following example:
Sys.UI.DomEvent.addHandler(element, 'click', this.myClickHandler);
You can also use the $addHandler shortcut, as shown in the following example:
$addHandler(element, 'click', this.myClickHandler);
The addHandler method takes three parameters: element, eventName, and handler. The element parameter is a reference to the DOM element that exposes the event. The eventName parameter is the name of the DOM event itself. The handler parameter is a reference to the function to call when the event is raised. For more information, see Sys.UI.DomEvent addHandler Method.
To remove a handler for a DOM event, you call the Sys.UI.DomEvent.removeHandler method or the $removeHandler shortcut, passing the same parameters that you pass to addHandler.
Note
Event names passed to the addHandler and removeHandler functions should not include the "on" prefix. For example, use "click", not "onclick".
Adding and Removing Custom Event Handlers
To add a new event handler for an event of a custom ASP.NET AJAX component, use the addHandler method of the Sys.EventHandlerList class. All client events and associated event handlers in the ASP.NET AJAX event model are stored in an EventHandlerList object, which is a specialized dictionary for that purpose. Every component, including the current Application object, has its own EventHandlerList instance. By adding an item to the EventHandlerList object, you add a new event and event handler to the associated component. Add events by using the following syntax:
this.get_events().addHandler(event, handler);
The events property of the Sys.Component class returns the EventHandlerList instance for that component. The events property is inherited by the Sys.UI.Control, Sys.UI.Behavior, and Sys.Application classes. The event parameter is the name of the new or existing event to add a handler for. The handler parameter is a reference to the function to call when the event is raised. By setting the event parameter to a new value, you add a new event to the dictionary.
To remove a custom event from the dictionary, you use the removeHandler method of the Sys.EventHandlerList class, which takes the same parameters as addHandler.
To add handlers to events that are already defined in the Microsoft Ajax Library, use the add_ accessor for that event, as in the following example:
Sys.Application.add_load(myLoadHandler);
Raising Custom Events
To raise a custom event, call the getHandler method of the EventHandlerList instance, passing the name of the event as a parameter. This method returns a function that aggregates all the functions that are handlers for that event. Call the returned function to raise the event, as in the following example:
var h = this.get_events().getHandler('myCustomEvent')
if (h) h(this, Sys.EventArgs.Empty);
By convention, event handlers take two parameters: sender and eventArgs. The sender is the component that the event applies to, typically this. The eventArgs parameter refers to a Sys.EventArgs object. This object can contain information passed to the event, such as mouse coordinates. You can omit the sender and eventArgs parameters, as long as the signature of the function returned by getHandler matches that of all the associated handler functions. However, the recommended practice is to include the parameters, as in the example shown earlier.
Example
Description
The following example creates a simple multiple-choice test with two sections. When all the questions in a section are answered, the section's background color changes. When the user clicks the button at the end of the test, a status message next to each question displays whether the answer is correct.
The application includes instances of two custom controls. The Question control attaches to an HTML <select> element, and the Section control attaches to a <div> element that contains one or more Question controls. The Question control exposes a select event, which is bound to the onChange event of the underlying <select> element by a Sys.UI.DomEvent instance. The Section control exposes a complete event, which is raised by a user-defined function when all the Question controls in the Section instance are answered.
Code
The following example shows the Default.aspx page that creates the component instances and handles the events.
<%@ Page Language="VB" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN"
"https://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd">
<html xmlns="https://www.w3.org/1999/xhtml">
<head id="Head1" runat="server">
<title>Custom Events Example</title>
</head>
<body>
<form id="form1" runat="server">
<asp:ScriptManager ID="ScriptManager1" runat="server" >
<Scripts>
<asp:ScriptReference Path="question.js" />
<asp:ScriptReference Path="section.js" />
</Scripts>
</asp:ScriptManager>
<script type="text/javascript">
// Add handler to init event
Sys.Application.add_init(appInitHandler);
function appInitHandler() {
// create components
$create(Demo.Question, {correct: '3'},
{select: onAnswer},null, $get('Question1'));
$create(Demo.Question, {correct: '3'},
{select: onAnswer},null, $get('Question2'));
$create(Demo.Question, {correct: '3'},
{select: onAnswer},null, $get('Question3'));
$create(Demo.Question, {correct: '3'},
{select: onAnswer},null, $get('Question4'));
$create(Demo.Section, null,
{complete: onSectionComplete},null, $get('group1'));
$create(Demo.Section, null,
{complete: onSectionComplete},null, $get('group2'));
}
function onAnswer(question) {
// If all questions in this section answered,
// raise complete event
var section = question.get_element().parentElement;
var questions = section.children;
$get(question.get_id() + 'Status').innerHTML = '';
for (var i=0; i<questions.length; i++) {
if (questions[i].selectedIndex === -1) {
return;
}
}
$find(section.id).raiseComplete();
}
function onSectionComplete(section) {
// Change background color of <div>.
section.get_element().style.backgroundColor = 'yellow';
}
function done() {
// Display correct answers where needed.
var c = Sys.Application.getComponents();
for (var i=0; i<c.length; i++) {
var type = Object.getType(c[i]).getName();
if (type !== 'Demo.Question') continue;
var element = c[i].get_element();
var answer = element.selectedIndex;
var correct = $find(c[i].get_id()).get_correct();
var statusElement = c[i].get_id() + 'Status';
if (answer !== correct) {
$get(statusElement).innerHTML = 'Incorrect. Try again.';
}
else
{
$get(statusElement).innerHTML = 'Correct.';
}
}
}
function resethandler() {
var c = Sys.Application.getComponents();
for (var i=0; i<c.length; i++) {
var type = Object.getType(c[i]).getName();
if (type === 'Demo.Question') {
var element = c[i].get_element();
element.selectedIndex = -1;
var answer = element.selectedIndex;
var statusElement = c[i].get_id() + 'Status';
$get(statusElement).innerHTML = '';
}
else if (type === 'Demo.Section') {
c[i].get_element().style.backgroundColor = 'White';
}
}
}
</script>
<h3>Addition</h3><br />
<div id="Group1">
2 + 2 =
<select id="Question1">
<option>2</option>
<option>22</option>
<option>4</option>
<option>5</option>
</select><span id="Question1Status"></span><br />
2 + 3 =
<select id="Question2" >
<option>3</option>
<option>23</option>
<option>5</option>
<option>6</option>
</select><span id="Question2Status"></span><br />
</div><br /> <br />
<h3>Subtraction</h3><br />
<div id="Group2">
2 - 1 =
<select id="Question3" >
<option>2</option>
<option>0</option>
<option>1</option>
<option>-2</option>
</select><span id="Question3Status"></span><br />
2 - 2 =
<select id="Question4" >
<option>2</option>
<option>-2</option>
<option>0</option>
<option>-4</option>
</select><span id="Question4Status"></span><br />
</div><br /><br />
<input id="Submit1" type="button" value="Check Answers" onclick="done()" />
<input id="Reset1" type="button" value="Start Again" onclick="resethandler()" />
</form>
</body>
</html>
<%@ Page Language="C#" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN"
"https://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd">
<html xmlns="https://www.w3.org/1999/xhtml">
<head id="Head1" runat="server">
<title>Custom Events Example</title>
</head>
<body>
<form id="form1" runat="server">
<asp:ScriptManager ID="ScriptManager1" runat="server" >
<Scripts>
<asp:ScriptReference Path="question.js" />
<asp:ScriptReference Path="section.js" />
</Scripts>
</asp:ScriptManager>
<script type="text/javascript">
// Add handler to init event
Sys.Application.add_init(appInitHandler);
function appInitHandler() {
// create components
$create(Demo.Question, {correct: '3'},
{select: onAnswer},null, $get('Question1'));
$create(Demo.Question, {correct: '3'},
{select: onAnswer},null, $get('Question2'));
$create(Demo.Question, {correct: '3'},
{select: onAnswer},null, $get('Question3'));
$create(Demo.Question, {correct: '3'},
{select: onAnswer},null, $get('Question4'));
$create(Demo.Section, null,
{complete: onSectionComplete},null, $get('group1'));
$create(Demo.Section, null,
{complete: onSectionComplete},null, $get('group2'));
}
function onAnswer(question) {
// If all questions in this section answered,
// raise complete event
var section = question.get_element().parentElement;
var questions = section.children;
$get(question.get_id() + 'Status').innerHTML = '';
for (var i=0; i<questions.length; i++) {
if (questions[i].selectedIndex === -1) {
return;
}
}
$find(section.id).raiseComplete();
}
function onSectionComplete(section) {
// Change background color of <div>.
section.get_element().style.backgroundColor = 'yellow';
}
function done() {
// Display correct answers where needed.
var c = Sys.Application.getComponents();
for (var i=0; i<c.length; i++) {
var type = Object.getType(c[i]).getName();
if (type !== 'Demo.Question') continue;
var element = c[i].get_element();
var answer = element.selectedIndex;
var correct = $find(c[i].get_id()).get_correct();
var statusElement = c[i].get_id() + 'Status';
if (answer !== correct) {
$get(statusElement).innerHTML = 'Incorrect. Try again.';
}
else
{
$get(statusElement).innerHTML = 'Correct.';
}
}
}
function resethandler() {
var c = Sys.Application.getComponents();
for (var i=0; i<c.length; i++) {
var type = Object.getType(c[i]).getName();
if (type === 'Demo.Question') {
var element = c[i].get_element();
element.selectedIndex = -1;
var answer = element.selectedIndex;
var statusElement = c[i].get_id() + 'Status';
$get(statusElement).innerHTML = '';
}
else if (type === 'Demo.Section') {
c[i].get_element().style.backgroundColor = 'White';
}
}
}
</script>
<h3>Addition</h3><br />
<div id="Group1">
2 + 2 =
<select id="Question1">
<option>2</option>
<option>22</option>
<option>4</option>
<option>5</option>
</select><span id="Question1Status"></span><br />
2 + 3 =
<select id="Question2" >
<option>3</option>
<option>23</option>
<option>5</option>
<option>6</option>
</select><span id="Question2Status"></span><br />
</div><br /> <br />
<h3>Subtraction</h3><br />
<div id="Group2">
2 - 1 =
<select id="Question3" >
<option>2</option>
<option>0</option>
<option>1</option>
<option>-2</option>
</select><span id="Question3Status"></span><br />
2 - 2 =
<select id="Question4" >
<option>2</option>
<option>-2</option>
<option>0</option>
<option>-4</option>
</select><span id="Question4Status"></span><br />
</div><br /><br />
<input id="Submit1" type="button" value="Check Answers" onclick="done()" />
<input id="Reset1" type="button" value="Start Again" onclick="resethandler()" />
</form>
</body>
</html>
The following example shows the Question.js file that defines the Demo.Question control.
Type.registerNamespace("Demo");
// Constructor
Demo.Question = function(element) {
Demo.Question.initializeBase(this, [element]);
// Create a delegate for the select event.
this._selectDelegate = null;
}
Demo.Question.prototype = {
// correct property accessors
get_correct: function() {
return this.get_element().name - 1;
},
set_correct: function(value) {
this.get_element().name = value;
},
// Bind and unbind to select event.
add_select: function(handler) {
this.get_events().addHandler('select', handler);
},
remove_select: function(handler) {
this.get_events().removeHandler('select', handler);
},
// Release resources before control is disposed.
dispose: function() {
var element = this.get_element();
if (this._selectDelegate) {
$clearHandlers(element);
delete this._selectDelegate;
}
Demo.Question.callBaseMethod(this, 'dispose');
},
initialize: function() {
var element = this.get_element();
// Make sure no option is selected.
element.value = "";
// Attach delegate to select event.
if (this._selectDelegate === null) {
this._selectDelegate = Function.createDelegate(this, this._selectHandler);
}
Sys.UI.DomEvent.addHandler(element, 'change', this._selectDelegate);
Demo.Question.callBaseMethod(this, 'initialize');
},
_selectHandler: function(event) {
var h = this.get_events().getHandler('select');
if (h) h(this, Sys.EventArgs.Empty);
}
}
Demo.Question.registerClass('Demo.Question', Sys.UI.Control);
// Since this script is not loaded by System.Web.Handlers.ScriptResourceHandler
// invoke Sys.Application.notifyScriptLoaded to notify ScriptManager
// that this is the end of the script.
if (typeof(Sys) !== 'undefined') Sys.Application.notifyScriptLoaded();
Type.registerNamespace("Demo");
// Constructor
Demo.Question = function(element) {
Demo.Question.initializeBase(this, [element]);
// Create a delegate for the select event.
this._selectDelegate = null;
}
Demo.Question.prototype = {
// correct property accessors
get_correct: function() {
return this.get_element().name - 1;
},
set_correct: function(value) {
this.get_element().name = value;
},
// Bind and unbind to select event.
add_select: function(handler) {
this.get_events().addHandler('select', handler);
},
remove_select: function(handler) {
this.get_events().removeHandler('select', handler);
},
// Release resources before control is disposed.
dispose: function() {
var element = this.get_element();
if (this._selectDelegate) {
$clearHandlers(element);
delete this._selectDelegate;
}
Demo.Question.callBaseMethod(this, 'dispose');
},
initialize: function() {
var element = this.get_element();
// Make sure no option is selected.
element.value = "";
// Attach delegate to select event.
if (this._selectDelegate === null) {
this._selectDelegate = Function.createDelegate(this, this._selectHandler);
}
Sys.UI.DomEvent.addHandler(element, 'change', this._selectDelegate);
Demo.Question.callBaseMethod(this, 'initialize');
},
_selectHandler: function(event) {
var h = this.get_events().getHandler('select');
if (h) h(this, Sys.EventArgs.Empty);
}
}
Demo.Question.registerClass('Demo.Question', Sys.UI.Control);
// Since this script is not loaded by System.Web.Handlers.ScriptResourceHandler
// invoke Sys.Application.notifyScriptLoaded to notify ScriptManager
// that this is the end of the script.
if (typeof(Sys) !== 'undefined') Sys.Application.notifyScriptLoaded();
The following example shows the Section.js file that defines the Demo.Section control.
Type.registerNamespace("Demo");
// Constructor
Demo.Section = function(element) {
Demo.Section.initializeBase(this, [element]);
}
Demo.Section.prototype = {
// Create add and remove accessors fot the complete event.
add_complete: function(handler) {
this.get_events().addHandler("complete", handler);
},
remove_complete: function(handler) {
this.get_events().removeHandler("complete", handler);
},
// Create a function to raise the complete event.
raiseComplete: function() {
var h = this.get_events().getHandler('complete');
if (h) h(this);
},
// Release resources before control is disposed.
dispose: function() {
var element = this.get_element();
$clearHandlers(element);
Demo.Section.callBaseMethod(this, 'dispose');
}
}
Demo.Section.registerClass('Demo.Section', Sys.UI.Control);
// Since this script is not loaded by System.Web.Handlers.ScriptResourceHandler
// invoke Sys.Application.notifyScriptLoaded to notify ScriptManager
// that this is the end of the script.
if (typeof(Sys) !== 'undefined') Sys.Application.notifyScriptLoaded();
Type.registerNamespace("Demo");
// Constructor
Demo.Section = function(element) {
Demo.Section.initializeBase(this, [element]);
}
Demo.Section.prototype = {
// Create add and remove accessors fot the complete event.
add_complete: function(handler) {
this.get_events().addHandler("complete", handler);
},
remove_complete: function(handler) {
this.get_events().removeHandler("complete", handler);
},
// Create a function to raise the complete event.
raiseComplete: function() {
var h = this.get_events().getHandler('complete');
if (h) h(this);
},
// Release resources before control is disposed.
dispose: function() {
var element = this.get_element();
$clearHandlers(element);
Demo.Section.callBaseMethod(this, 'dispose');
}
}
Demo.Section.registerClass('Demo.Section', Sys.UI.Control);
// Since this script is not loaded by System.Web.Handlers.ScriptResourceHandler
// invoke Sys.Application.notifyScriptLoaded to notify ScriptManager
// that this is the end of the script.
if (typeof(Sys) !== 'undefined') Sys.Application.notifyScriptLoaded();
See Also
Tasks
Creating Custom AJAX Client Controls