Google Choice: Sencha Touch

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Sunday, March 12, 2017

Sencha Touch - Events

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:

Built in events using listeners
Attaching events later
Custom events

Built in events using listeners

Sencha Touch provides listener property for writing events and custom events in Sencha Touch files.
Writing listener in Sencha Touch
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://cdn.sencha.com/touch/sencha-touch-2.4.2/resources/css/sencha-touch.css" rel="stylesheet" />
      <script type="text/javascript" src="https://cdn.sencha.com/touch/sencha-touch-2.4.2/sencha-touch-all.js"></script>
      <script type="text/javascript">
         Ext.application({
            name: 'Sencha',
            launch: function() {
               Ext.create('Ext.Panel', {
                  html: 'My Panel',
                  fullscreen: true,
                  listeners: {
                     painted: function() {
                        Ext.Msg.alert('I was painted to the screen');
                     }
                  }
               });
            }
         });
      </script> 
   </head>
</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://cdn.sencha.com/touch/sencha-touch-2.4.2/resources/css/sencha-touch.css" rel="stylesheet" />
      <script type="text/javascript" src="https://cdn.sencha.com/touch/sencha-touch-2.4.2/sencha-touch-all.js"></script>
      <script type="text/javascript">   
         Ext.application({
            name: 'Sencha',
            launch: function() {
               var myButton = Ext.Viewport.add({
                  xtype: 'button',
                  centered: true,
                  text: 'Click me'
               });

               myButton.on({
                  tap: function() {
                     var randomWidth = 100 + Math.round(Math.random() * 200);
                     this.setWidth(randomWidth);
                  },
                  widthchange: function(button, newWidth, oldWidth) {
                     alert('My width changed from ' + oldWidth + ' to ' + newWidth);
                  }
               });
            }
         });       
      </script> 
   </head>
</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://cdn.sencha.com/touch/sencha-touch-2.4.2/resources/css/sencha-touch.css" rel="stylesheet" />
      <script type="text/javascript" src="https://cdn.sencha.com/touch/sencha-touch-2.4.2/sencha-touch-all.js"></script>
      <script type="text/javascript">
         Ext.application({
            name: 'Sencha',
            launch: function() {
               var myButton = Ext.Viewport.add({
                  xtype: 'button',
                  centered: true,
                  text: 'Click me'
               });
               
               myButton.on('tap', function() {
                  alert("Event listener attached by .on");
               });
            }
         });
      </script> 
   </head>
</html>

Custom events

We can write custom events in Sencha Touch and fire the events with fireEvent method, below example explains how to write a custom events.

<!DOCTYPE html>
<html>
   <head>
      <link href="https://cdn.sencha.com/touch/sencha-touch-2.4.2/resources/css/sencha-touch.css" rel="stylesheet" />
      <script type="text/javascript" src="https://cdn.sencha.com/touch/sencha-touch-2.4.2/sencha-touch-all.js"></script>
      <script type="text/javascript">
         Ext.application({
            name: 'Sencha',
            launch: function() {
               var myButton = Ext.Viewport.add({
                  xtype: 'button',
                  centered: true,
                  text: "Just wait 5 seconds",

                  listeners: {
                     myEvent: function(button, points) {
                        alert('myEvent was fired! You score ' + points + ' points');
                     }
                  }
               });

               Ext.defer(function() {
                  var number = Math.ceil(Math.random() * 100);
                  myButton.fireEvent('myEvent', myButton, number);
               }, 5000);
            }
         });
      </script> 
   </head>
</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 Sencha Touch.

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