Friday, February 17, 2017

Ext.js - Custom Events and listeners

Events are something which get fired when something happens to the class. For example when a button is getting clicked or before/ after element is rendered.

Methods of writing events:

  1. Built in events using listeners
  2. Attaching events later
  3. Custom events

Built in events using listeners

Ext JS provides listener property for writing events and custom events in Ext JS files.
Writing listener in Ext JS
We will add the listener in the previous program itself by adding listen property to the panel as below:
<!DOCTYPE html>
<html>
   <head>
      <link href="https://cdnjs.cloudflare.com/ajax/libs/extjs/6.0.0/classic/theme-neptune/resources/theme-neptune-all.css" rel="stylesheet" />
      <script type="text/javascript" src="https://cdnjs.cloudflare.com/ajax/libs/extjs/6.0.0/ext-all.js"></script>
      <script type="text/javascript">
         Ext.onReady(function(){
            Ext.create('Ext.Button', {
               renderTo: Ext.getElementById('helloWorldPanel'),
               text: 'My Button',
               listeners: {
                  click: function() {
                     Ext.MessageBox.alert('Alert box', 'Button is clicked'); 
                  }
               }
            });
         });
      </script> 
   </head>
   <body>
      <p> Please click the button to see event listener </p>
      <div id = 'helloWorldPanel' />   <!--  panel will be rendered here-- >
   </body>
</html>
This will produce following result:
This way we can write multiple events also in listeners property.
Multiple events in same listener
<!DOCTYPE html>
<html>
   <head>
      <link href="https://cdnjs.cloudflare.com/ajax/libs/extjs/6.0.0/classic/theme-neptune/resources/theme-neptune-all.css" rel="stylesheet" />
      <script type="text/javascript" src="https://cdnjs.cloudflare.com/ajax/libs/extjs/6.0.0/ext-all.js"></script>
      <script type="text/javascript">
         Ext.onReady(function(){
            Ext.get('tag2').hide()
            Ext.create('Ext.Button', {
               renderTo: Ext.getElementById('helloWorldPanel'),
               text: 'My Button',
               listeners: {
                  click: function() {
                     this.hide();
                  },
                  hide: function() {
                     Ext.get('tag1').hide();
                     Ext.get('tag2').show();
                  }
               }
            });
         });           
      </script> 
   </head>
   <body>
   <div id = "tag1">Please click the button to see event listener.</div>
   <div id = "tag2">The button was clicked and now it is hidden.</div>
   <div id = 'helloWorldPanel' />   <!--  panel will be rendered here-- >
   </body>
</html>

Attaching event later

In the previous method of writing events we have written events in listeners at the time of creating elements.
Other way is to attach events in the as:
<!DOCTYPE html>
<html>
   <head>
      <link href="https://cdnjs.cloudflare.com/ajax/libs/extjs/6.0.0/classic/theme-neptune/resources/theme-neptune-all.css" rel="stylesheet" />
      <script type="text/javascript" src="https://cdnjs.cloudflare.com/ajax/libs/extjs/6.0.0/ext-all.js"></script>
      <script type="text/javascript">
         Ext.onReady(function(){
            var button = Ext.create('Ext.Button', {
               renderTo: Ext.getElementById('helloWorldPanel'),
            text: 'My Button'
            });

            // This way we can attach event to the button after the button is created.
            button.on('click', function() {
               Ext.MessageBox.alert('Alert box', 'Button is clicked');
            });
         });
      </script> 
   </head>
   <body>
      <p> Please click the button to see event listener </p>
      <div id = 'helloWorldPanel' />   <!--  panel will be rendered here-- >
   </body>
</html>

Custom events

We can write custom events in ext JS and fire the events with fireEvent method, below example explains how to write a custom events.
<!DOCTYPE html>
<html>
   <head>
      <link href="https://cdnjs.cloudflare.com/ajax/libs/extjs/6.0.0/classic/theme-neptune/resources/theme-neptune-all.css" rel="stylesheet" />
      <script type="text/javascript" src="https://cdnjs.cloudflare.com/ajax/libs/extjs/6.0.0/ext-all.js"></script>
      <script type="text/javascript">
         Ext.onReady(function(){
            var button = Ext.create('Ext.Button', {
               renderTo: Ext.getElementById('helloWorldPanel'),
               text: 'My Button',
               listeners: {
                  myEvent: function(button) {
                     Ext.MessageBox.alert('Alert box', 'My custom event is called');
                  }
               }
            });
            Ext.defer(function() {
               button.fireEvent('myEvent');
            }, 5000);
         }); 
      </script> 
   </head>
   <body>
      <p> The event will be called after 5 seconds when the page is loaded. </p>
      <div id = 'helloWorldPanel' />   <!--  panel will be rendered here-- >
   </body>
</html>
Once the page is loaded and document is ready the UI page with button will appear and as we are firing an event after 5 sec the document is ready the alert box will appear after 5 seconds.
Here we have written the custom event 'myEvent' and we are firing events as button.fireEvent(eventName);
These are the three ways of writing events in Ext JS.
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