You cannot use the return value of an API function call as result is not know at the moment of the call return. It is never stressed enough that Ext.Direct calls are ASYNCHRONOUS.

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Code in this post can be obsolete, however, principles and theory may still apply.

<<< Mastering Ext.Direct, Part 2

Processing responses

As I’ve already said, you cannot use the return value of an API function call as result is not know at the moment of the call return. It is never stressed enough that Ext.Direct calls are ASYNCHRONOUS. Therefore, all Ext.Direct created API functions, for example Example.Car.go() take one extra argument in addition to arguments you have specified in server-side class definition. That argument is callback function. In our example, Example.Car.go() takes one argument, speed per server side method definition, however, it takes two in fact: Example.Car.go(speed, callback) Let’s call it with a callback to test it. Type in the Firebug console:
Example.Car.go(80, console.info);
console.info is a function that prints its arguments in a human readable form. We use it as the callback so we see:
  • that it really gets called when the response arrives
  • which arguments Ext.Direct passes to the callback
As you can see, the callback is called with two arguments:
  • response – it is that what is returned by the server-side Car.go() method. It can be string (as in our example), boolean, object, array or void (nothing).
  • e – it is Ext.Direct.Event object or, being more specific, Ext.Direct.RemotingEvent.
  The event e has some useful properties and methods, most important of them are:
  • status is true if the call was successful, false if the call failed
  • result contains same value as the first argument – it is server response data
  • type is rpc in our example but it also can be exception or others
  • action is the class name
  • method is name of the method called
  • getTransaction() is method to retrieve the transaction used in this server round trip. You would use it if you want more data on the transaction.
 

Processing exceptions

Let’s call go method again:
Example.Car.go(300, console.info);
The callback is called as before but the arguments differ:
  • response is undefined – no data from server
  • e has type exception and has property message that contains error message text

An example application

That is almost all we need to know to start using Ext.Direct in an application. I’ve written a simple one so you have something to play with. First, create file example.js with the following content:
/**
 * Mastering Ext.Direct example script
 *
 * @author     Ing. Jozef Sakalos
 * @copyright  (c) 2009, by Ing. Jozef Sakalos
 * @date       16. September 2009
 * @version    1.0
 * @revision   $Id$
 */

Ext.BLANK_IMAGE_URL='ext/resources/images/default/s.gif';

Ext.onReady(function() {
    /**
     * This function is called when Ext.Direct request
     * response arrives from the server.
     *
     * @param {String/Object/Array/Null} response 
     * That what is returned by server method
     * @param {Ext.Direct.RemotingEvent/Ext.Direct.ExceptionEvent} e 
     */
    var callback = function(response, e) {

        // uncomment if you want to inspect arguments in Firebug Console
//        console.log(response, e);

        var status = 'Success'
        var text = '';

        // success handling - e.status is success flag: 
        // true is success, false is failure
        if(true === e.status) {
            // response argument is same as e.result
            text = response;
        }

        // failure handling
        else {
            status = 'Failure'

            // in the case of an exception, we don't have response but message
            text = e.message;
        }

        // grab the center body
        var body = win.items.itemAt(1).body;

        // display the response
        body.createChild({
             tag:'div'
            ,cls:'response'
            ,html:status + ': ' + text
        });

        // scroll down
        body.scrollTo('top', 100000, true);
    };

    // create Ext.Direct test window
    var win = new Ext.Window({
         title:'Mastering Ext.Direct by Saki'
        ,width:600
        ,height:400
        ,closable:false
        ,layout:'border'
        ,border:false
        ,items:[{
            // west region with buttons
             region:'west'
            ,width:160
            ,minSize:160
            ,split:true
            ,defaults:{minWidth:120}
            ,layout:'table'
            ,bodyStyle:'padding:20px'
            ,layoutConfig:{columns:1, tableAttrs:{style:{width:'100%'}}}
            ,items:[{
                 xtype:'button'
                ,text:'Car.start()'

                // a delegate is needed if we want to pass arguments
                ,handler:Example.Car.start.createDelegate(null, [callback])
            },{
                 xtype:'button'
                ,text:'Car.go(80)'

                // a delegate is needed if we want to pass arguments
                ,handler:Example.Car.go.createDelegate(null, [80, callback])
            },{
                 xtype:'button'
                ,text:'Car.go(250)'

                // a delegate is needed if we want to pass arguments
                ,handler:Example.Car.go.createDelegate(null, [250, callback])
            },{
                 xtype:'button'
                ,text:'Car.stop()'

                // a delegate is needed if we want to pass arguments
                ,handler:Example.Car.stop.createDelegate(null, [callback])
            },{
                 xtype:'button'
                ,text:'Send All'

                // another option is inline function that executes calls
                ,handler:function() {

                    // the following calls will be combined in one request
                    Example.Car.start(callback);
                    Example.Car.go(80, callback);
                    Example.Car.go(250, callback);
                    Example.Car.stop(callback);
                }
            }]
        },{
            // responses are displayed here
             region:'center'
            ,autoScroll:true
            ,tbar:['->', {
                text:'Clear'
               ,handler:function(){win.items.itemAt(1).body.update('')}
            }]
        }]
    });
    win.show();

});

// eof
  Then tune your index.php so that it reads:
Mastering Ext.Direct by Saki

      .x-table-layout-cell {
        height:40px;
        text-align:center;
        vertical-align:middle;
    }
    .x-table-layout-cell table {
        margin:auto
    }
    .response {
        padding:4px 0 4px 20px;
        font-size:13px;
    }

      Ext.Direct.addProvider(Example.API);
 

Conclusion

Good! Play with Ext.Direct and let me know what you would like to have in next parts.
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