Questions tagged [event-handling]
Event handling is a coding style about handling messages between a source and one or more subscribers. A point listener in the source provide a way which subscribed code can consume messages raised from the source.
event-handling
12,836
questions
3248
votes
14
answers
938k
views
event.preventDefault() vs. return false
When I want to prevent other event handlers from executing after a certain event is fired, I can use one of two techniques. I'll use jQuery in the examples, but this applies to plain-JS as well:
1. ...
- 70k
896
votes
9
answers
2.5m
views
window.onload vs document.onload
Which is more widely supported: window.onload or document.onload?
- 34.1k
759
votes
13
answers
1.2m
views
jQuery checkbox checked state changed event
I want an event to fire client side when a checkbox is checked / unchecked:
$('.checkbox').click(function() {
if ($(this).is(':checked')) {
// Do stuff
}
});
Basically I want it to happen ...
- 18.4k
710
votes
21
answers
1.9m
views
jQuery checkbox change and click event
$(document).ready(function() {
//set initial state.
$('#textbox1').val($(this).is(':checked'));
$('#checkbox1').change(function() {
$('#textbox1').val($(this).is(':checked'));
});
...
- 9,000
641
votes
22
answers
420k
views
UITextField text change event
How can I detect any text changes in a textField? The delegate method shouldChangeCharactersInRange works for something, but it did not fulfill my need exactly. Since until it returns YES, the ...
- 15.5k
618
votes
15
answers
243k
views
How to debug JavaScript / jQuery event bindings with Firebug or similar tools?
I need to debug a web application that uses jQuery to do some fairly complex and messy DOM manipulation. At one point, some of the events that were bound to particular elements, are not fired and ...
- 17.8k
594
votes
2
answers
847k
views
How can I trigger an onchange event manually? [duplicate]
I'm setting a date-time textfield value via a calendar widget. Obviously, the calendar widget does something like this :
document.getElementById('datetimetext').value = date_value;
What I want is:
On ...
- 6,211
389
votes
16
answers
131k
views
Why are only final variables accessible in anonymous class?
a can only be final here. Why? How can I reassign a in onClick() method without keeping it as private member?
private void f(Button b, final int a){
b.addClickHandler(new ClickHandler() {
...
user467871
365
votes
13
answers
444k
views
Understanding events and event handlers in C#
I understand the purpose of events, especially within the context of creating user interfaces. I think this is the prototype for creating an event:
public void EventName(object sender, EventArgs e);
...
- 6,045
319
votes
10
answers
138k
views
Difference between e.target and e.currentTarget
I don't understand the difference, they both seem the same but I guess they are not.
Any examples of when to use one or the other would be appreciated.
- 8,575
317
votes
9
answers
336k
views
jQuery - Detect value change on hidden input field
I have a hidden text field whose value gets updated via an AJAX response.
<input type="hidden" value="" name="userid" id="useid" />
When this value changes, I would like to fire an AJAX ...
- 6,076
311
votes
2
answers
449k
views
How can I capture the right-click event in JavaScript? [duplicate]
I want to block the standard context menus, and handle the right-click event manually.
How is this done?
- 20.8k
306
votes
11
answers
288k
views
How to call function on child component on parent events
Context
In Vue 2.0 the documentation and others clearly indicate that communication from parent to child happens via props.
Question
How does a parent tell its child an event has happened via props?...
- 3,733
279
votes
14
answers
135k
views
Android: Difference between onInterceptTouchEvent and dispatchTouchEvent?
What is the difference between onInterceptTouchEvent and dispatchTouchEvent in Android?
According to the android developer guide, both methods can be used to intercept a touch event (MotionEvent), ...
- 3,191
277
votes
3
answers
6k
views
JavaScript click handler not working as expected inside a for loop [duplicate]
I'm trying to learn JS and got an issue.
I tried many things and googled but all in vain. Following piece of code doesn't work as expected. I should get value of i on click but it always returns 6. I'...
- 3,273
270
votes
10
answers
151k
views
What is DOM Event delegation?
Can anyone please explain event delegation in JavaScript and how is it useful?
- 2,717
266
votes
1
answer
112k
views
How to remove a lambda event handler [duplicate]
I recently discovered that I can use lambdas to create simple event handlers. I could for example subscribe to a click event like this:
button.Click += (s, e) => MessageBox.Show("Woho");
...
- 155k
254
votes
16
answers
315k
views
Which Python packages offer a stand-alone event system? [closed]
I am aware of pydispatcher, but there must be other event-related packages around for Python.
Which libraries are available?
I'm not interested in event managers that are part of large frameworks, I'd ...
- 6,705
247
votes
41
answers
261k
views
Detecting Browser Autofill
How do you tell if a browser has auto filled a text-box? Especially with username & password boxes that autofill around page load.
My first question is when does this occur in the page load ...
- 11.3k
221
votes
7
answers
574k
views
jQuery equivalent of JavaScript's addEventListener method
I'm trying to find the jQuery equivalent of this JavaScript method call:
document.addEventListener('click', select_element, true);
I've gotten as far as:
$(document).click(select_element);
but ...
- 19.6k
216
votes
10
answers
380k
views
How can I remove a JavaScript event listener?
I'm trying to remove an event listener inside of a listener definition:
canvas.addEventListener('click', function(event) {
click++;
if(click == 50) {
// remove this event listener here!...
- 2,161
208
votes
4
answers
35k
views
Do event handlers stop garbage collection from occurring?
If I have the following code:
MyClass pClass = new MyClass();
pClass.MyEvent += MyFunction;
pClass = null;
Will pClass be garbage collected? Or will it hang around still firing its events whenever ...
- 72.7k
204
votes
5
answers
80k
views
Why and How to avoid Event Handler memory leaks?
I just came to realize, by reading some questions and answers on StackOverflow, that adding event handlers using += in C# (or i guess, other .net languages) can cause common memory leaks...
I have ...
- 8,840
195
votes
5
answers
291k
views
How to pass event as argument to an inline event handler in JavaScript?
// this e works
document.getElementById("p").oncontextmenu = function(e) {
e = e || window.event;
var target = e.target || e.srcElement;
console.log(target);
};
// this e is undefined
function ...
- 4,497
174
votes
8
answers
341k
views
How do I add a simple onClick event handler to a canvas element?
I'm an experienced Java programmer but am looking at some JavaScript/HTML5 stuff for the first time in about a decade. I'm completely stumped on what should be the simplest thing ever.
As an example ...
- 5,548
169
votes
8
answers
198k
views
How can I be notified when an element is added to the page?
I want a function of my choosing to run when a DOM element is added to the page. This is in the context of a browser extension, so the webpage runs independently of me and I cannot modify its source. ...
- 63k
167
votes
4
answers
176k
views
145
votes
6
answers
327k
views
Handling a Menu Item Click Event - Android
I want to create an intent that starts a new activity once a Menu Item is clicked, but I'm not sure how to do this. I've been reading through the android documentation, but my implementation isn't ...
- 4,738
143
votes
8
answers
128k
views
jQuery: more than one handler for same event
What happens if I bind two event handlers to the same event for the same element?
For example:
var elem = $("...")
elem.click(...);
elem.click(...);
Does the last handler "win", or will both ...
- 267k
139
votes
5
answers
121k
views
Detecting CTRL+C in Node.js
I got this code from a different SO question, but node complained to use process.stdin.setRawMode instead of tty, so I changed it.
Before:
var tty = require("tty");
process.openStdin().on("keypress"...
- 2,993
135
votes
2
answers
207k
views
Pass parameter to EventHandler [duplicate]
I have the following EventHandler to which I added a parameter MusicNote music:
public void PlayMusicEvent(object sender, EventArgs e,MusicNote music)
{
music.player.Stop();
System.Timers....
- 3,890
132
votes
5
answers
108k
views
Explain ExtJS 4 event handling
I've recently started learning ExtJS, and have trouble understanding how to handle Events. I have no experience of any previous versions of ExtJS.
From reading various manuals, guides and ...
- 26.3k
131
votes
18
answers
84k
views
How can I change the EditText text without triggering the Text Watcher?
I have an EditText field with a Customer Text Watcher on it. In a piece of code I need to change the value in the EditText which I do using .setText("whatever").
The problem is as soon as I make that ...
- 1,481
131
votes
3
answers
108k
views
JavaScript: Listen for attribute change?
Is it possible in JavaScript to listen for a change of attribute value? For example:
var element=document.querySelector('…');
element.addEventListener( ? ,doit,false);
element.setAttribute('...
- 15.2k
129
votes
15
answers
213k
views
Put length constraint in a TextField in react js
I am taking an input from the user of the card number and wants that the length entered by user must not be less than and more than 12. Here is the declaration of my textfield.
<TextField
id="...
- 1,885
128
votes
9
answers
277k
views
Javascript event handler with parameters
I want to make an eventHandler that passes the event and some parameters. The problem is that the function doesn't get the element. Here is an example:
doClick = function(func){
var elem = .. // ...
- 2,043
126
votes
2
answers
45k
views
Is it necessary to explicitly remove event handlers in C#
I have a class that offers up a few events. That class is declared globally but not instanced upon that global declaration--it's instanced on an as-needed basis in the methods that need it.
Each ...
- 17.6k
123
votes
6
answers
271k
views
How to trigger event when a variable's value is changed?
I'm currently creating an application in C# using Visual Studio. I want to create some code so that when a variable has a value of 1 then a certain piece of code is carried out.
I know that I can use ...
- 4,309
123
votes
6
answers
269k
views
Get clicked element using jQuery on event?
I'm using the following code to detect when a dynamically generated button is clicked.
$(document).on("click",".appDetails", function () {
alert("test");
});
Normally, if you just did $('....
user736893
119
votes
8
answers
305k
views
How to remove "onclick" with JQuery?
PHP code:
<a id="a$id" onclick="check($id,1)" href="javascript:void(0)" class="black">Qualify</a>
I want to remove the onclick="check($id,1) so the link cannot be clicked or "check($id,...
- 24.8k
116
votes
8
answers
48k
views
jQuery: $().click(fn) vs. $().bind('click',fn);
When using jQuery to hookup an event handler, is there any difference between using the click method
$().click(fn)
versus using the bind method
$().bind('click',fn);
Other than bind's optional ...
- 165k
115
votes
7
answers
78k
views
When should I use jQuery's document.ready function?
I was told to use document.ready when I first started to use Javascript/jQuery but I never really learned why.
Might someone provide some basic guidelines on when it makes sense to wrap javascript/...
- 23.9k
114
votes
9
answers
107k
views
C# pattern to prevent an event handler hooked twice [duplicate]
Duplicate of: How to ensure an event is only subscribed to once
and Has an event handler already been added?
I have a singleton that provides some service and my classes hook into some events on it, ...
- 5,161
112
votes
13
answers
62k
views
Order of event handler execution
If I set up multiple event handlers, like so:
_webservice.RetrieveDataCompleted += ProcessData1;
_webservice.RetrieveDataCompleted += ProcessData2;
what order are the handlers run when the event ...
- 15.8k
105
votes
7
answers
102k
views
Changing UIButton text
So I'm trying to update the text on a UIButton when I click it. I'm using the following line to change the text:
calibrationButton.titleLabel.text = @"Calibration";
I have verified that the text is ...
- 3,599
99
votes
4
answers
89k
views
event.preventDefault() vs. return false (no jQuery)
I wondered if event.preventDefault() and return false were the same.
I have done some tests, and it seems that
If the event handler is added using old model, for example
elem.onclick = function(){
...
- 281k
96
votes
7
answers
66k
views
Handle URL fragment identifier (anchor) change event in Javascript
How can I write the Javascript callback code that will be executed on any changes in the URL fragment identifier (anchor)?
For example from http://example.com#a to http://example.com#b
- 8,187
93
votes
6
answers
100k
views
How to removeEventListener that is addEventListener with anonymous function?
function doSomethingWith(param)
{
document.body.addEventListener(
'scroll',
function()
{
document.write(param);
},
false
); // An event that ...
- 2,759
91
votes
6
answers
119k
views
How to trigger function on value change?
I realise this question has to do with event-handling and i've read about Python event-handler a dispatchers, so either it did not answer my question or i completely missed out the information.
I ...
- 7,123
87
votes
16
answers
64k
views
Difference between event handlers and callbacks
What is the difference between an event handler and a callback function?
- 5,173