Explain ExtJS 4 event handling

Question

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 documentation pages  I ve figured out how to use it  but I m not clear on how it works  I ve found several tutorials for older versions of ExtJS  but I m not sure how applicable they are in ExtJS 4   I m specifically looking on the  final word  on things like   what arguments does an event handling function get passed  Is there a standard set of args that always get passed  how to define custom events for custom components we write  how can we fire these custom event  does the return value  true false  affect how the event bubbles  If not  how can we control event bubbling from within  or outside of the event handler  is there a standard way to register event listeners   I ve come across two different ways til now  and I m not sure why each method was used     For example  this question leads me to believe that an event handler can receive quite a few arguments  I ve seen other tutorials where there are just two arguments to the handler  What changes

User · Answer

Just wanted to add a couple of pence to the excellent answers above: If you are working on pre Extjs 4.1, and don't have application wide events but need them, I've been using a very simple technique that might help: Create a simple object extending Observable, and define any app wide events you might need in it. You can then fire those events from anywhere in your app, including actual html dom element and listen to them from any component by relaying the required elements from that component.

Ext.define('Lib.MessageBus', {
    extend: 'Ext.util.Observable',

    constructor: function() {
        this.addEvents(
            /*
             * describe the event
             */
                  "eventname"

            );
        this.callParent(arguments);
    }
});

Then you can, from any other component:

 this.relayEvents(MesageBus, ['event1', 'event2'])

And fire them from any component or dom element:

 MessageBus.fireEvent('event1', somearg);

 <input type="button onclick="MessageBus.fireEvent('event2', 'somearg')">

User · Answer

Firing application wide events  How to make controllers talk to each other      In addition to the very great answer above I want to mention application wide events which can be very useful in an MVC setup to enable communication between controllers   extjs4 1   Lets say we have a controller Station  Sencha MVC examples  with a select box   Ext define  Pandora controller Station         extend   Ext app Controller                init  function             this control                stationslist                     selectionchange  this onStationSelect                                                                 onStationSelect  function selModel  selection            this application fireEvent  stationstart   selection 0                            When the select box triggers a change event  the function onStationSelect is fired   Within that function we see   this application fireEvent  stationstart   selection 0      This creates and fires an application wide event that we can listen to from any other controller   Thus in another controller we can now know when the station select box has been changed  This is done through listening to this application on as follows   Ext define  Pandora controller Song         extend   Ext app Controller                init  function             this control                recentlyplayedscroller                     selectionchange  this onSongSelect                                       Listen for an application wide event         this application on               stationstart  this onStationStart                   scope  this                                 onStationStart  function station            console info  I called to inform you that the Station controller select box just has been changed            console info  Now what do you want to do next                If the selectbox has been changed we now fire the function onStationStart in the controller Song also      From the Sencha docs   Application events are extremely useful for events that have many controllers  Instead of listening for the same view event in each of these controllers  only one controller listens for the view event and fires an application-wide event that the others can listen for  This also allows controllers to communicate with one another without knowing about or depending on each other   s existence   In my case  Clicking on a tree node to update data in a grid panel   Update 2016 thanks to  gm2008 from the comments below   In terms of firing application-wide custom events  there is a new method now after ExtJS V5 1 is published  which is using Ext GlobalEvents    When you fire events  you can call  Ext GlobalEvents fireEvent  custom event     When you register a handler of the event  you call  Ext GlobalEvents on  custom event   function arguments     handler codes     scope    This method is not limited to controllers  Any component can handle a custom event through putting the component object as the input parameter scope   Found in Sencha Docs  MVC Part 2

User · Answer

Just two more things I found helpful to know  even if they are not part of the question  really   You can use the relayEvents method to tell a component to listen for certain events of another component and then fire them again as if they originate from the first component  The API docs give the example of a grid relaying the store load event  It is quite handy when writing custom components that encapsulate several sub-components   The other way around  i e  passing on events received by an encapsulating component mycmp to one of its sub-components subcmp  can be done like this  mycmp on  show  function  mycmp  eOpts       mycmp subcmp fireEvent  show   mycmp subcmp  eOpts

User · Answer

One more trick for controller event listeners   You can use wildcards to watch for an event from any component   this control                    myCustomEvent  this doSomething

User · Answer

Let s start by describing DOM elements  event handling   DOM node event handling  First of all you wouldn t want to work with DOM node directly  Instead you probably would want to utilize Ext Element interface  For the purpose of assigning event handlers  Element addListener and Element on  these are equivalent  were created  So  for example  if we have html    lt div id  test node  gt  lt  div gt    and we want add click event handler  Let s retrieve Element   var el   Ext get  test node      Now let s check docs for click event  It s handler may have three parameters      click  Ext EventObject e  HTMLElement t  Object eOpts     Knowing all this stuff we can assign handler            event name      event handler el on      click           function e  t  eOpts        handling event here       Widgets event handling  Widgets event handling is pretty much similar to DOM nodes event handling     First of all  widgets event handling is realized by utilizing Ext util Observable mixin  In order to handle events properly your widget must containg Ext util Observable as a mixin  All built-in widgets  like Panel  Form  Tree  Grid       has Ext util Observable as a mixin by default   For widgets there are two ways of assigning handlers  The first one - is to use on method  or addListener   Let s for example create Button widget and assign click event to it  First of all you should check event s docs for handler s arguments      click  Ext button Button this  Event e  Object eOpts     Now let s use on   var myButton   Ext create  Ext button Button       text   Test button      myButton on  click   function btn  e  eOpts         event handling here   console log btn  e  eOpts         The second way is to use widget s listeners config   var myButton   Ext create  Ext button Button       text   Test button     listeners         click  function btn  e  eOpts             event handling here       console log btn  e  eOpts                   Notice that Button widget is a special kind of widgets  Click event can be assigned to this widget by using handler config   var myButton   Ext create  Ext button Button       text   Test button     handler   function btn  e  eOpts           event handling here     console log btn  e  eOpts             Custom events firing  First of all you need to register an event using addEvents method   myButton addEvents  myspecialevent1    myspecialevent2    myspecialevent3                 Using the addEvents method is optional  As comments to this method say there is no need to use this method but it provides place for events documentation   To fire your event use fireEvent method   myButton fireEvent  myspecialevent1   arg1  arg2  arg3                arg1  arg2  arg3            will be passed into handler  Now we can handle your event   myButton on  myspecialevent1   function arg1  arg2  arg3                    event handling here   console log arg1  arg2  arg3                    It s worth mentioning that the best place for inserting addEvents method call is widget s initComponent method when you are defining new widget   Ext define  MyCustomButton       extend   Ext button Button            other configs    initComponent  function        this addEvents  myspecialevent1    myspecialevent2    myspecialevent3                              this callParent arguments           var myButton   Ext create  MyCustomButton        configs          Preventing event bubbling  To prevent bubbling you can return false or use Ext EventObject preventDefault    In order to prevent browser s default action use Ext EventObject stopPropagation     For example let s assign click event handler to our button  And if not left button was clicked prevent default browser action   myButton on  click   function btn  e     if  e button     0      e preventDefault

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