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YUI Library Examples: Widget: Creating a widget plugin

Widget: Creating a widget plugin

This example shows how you can use Widget's plugin infrastructure to add additional features to an existing widget.

We create an IO plugin class for Widget called WidgetIO. The plugin adds IO capabilities to the Widget, which, by default, outputs to the Widget's contentBox.

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Creating an IO Plugin For Widget

Setting Up The YUI Instance

For this example, we'll pull in widget; the io, and the plugin module. The io module provides the XHR support we need for the IO plugin. The Plugin base class is the class we'll extend to create our io plugin class for Widget. The code to set up our sandbox instance is shown below:

  1. YUI({...}).use("widget", "io", "plugin", function(Y) {
  2.     // We'll write our code here, after pulling in the default Widget module, 
  3.     // the IO utility, and the Plugin base class.
  4. }
YUI({...}).use("widget", "io", "plugin", function(Y) {
    // We'll write our code here, after pulling in the default Widget module, 
    // the IO utility, and the Plugin base class.
}

Using the widget module will also pull down the default CSS required for widget, on top of which we only need to add our required look/feel CSS for the example.

WidgetIO Class Structure

The WidgetIO class will extend the Plugin base class. Since Plugin derives from Base, we follow the same pattern we use for widgets and other utilities which extend Base to setup our new class.

Namely:

  • Setting up the constructor to invoke the superclass constructor
  • Setting up a NAME property, to identify the class
  • Setting up the default attributes, using the ATTRS property
  • Providing prototype implementations for anything we want executed during initialization and destruction using the initializer and destructor lifecycle methods

Additionally, since this is a plugin, we provide a NS property for the class, which defines the property which will refer to the WidgetIO instance on the host class (e.g. widget.io will be an instance of WidgetIO)

. 
  1. /* Widget IO Plugin Constructor */
  2. function WidgetIO(config) {
  3.     WidgetIO.superclass.constructor.apply(this, arguments);
  4. }
  5.  
  6. /* 
  7.  * The namespace for the plugin. This will be the property on the widget, 
  8.  * which will reference the plugin instance, when it's plugged in
  9.  */
  10. WidgetIO.NS = "io";
  11.  
  12. /*
  13.  * The NAME of the WidgetIO class. Used to prefix events generated
  14.  * by the plugin class.
  15.  */
  16. WidgetIO.NAME = "ioPlugin";
  17.  
  18. /*
  19.  * The default set of attributes for the WidgetIO class.
  20.  */
  21. WidgetIO.ATTRS = {
  22.     uri : {...},
  23.     cfg : {...},
  24.     formatter : {...},
  25.     loading: {...}
  26. };
  27.  
  28. /* Extend the base plugin class */
  29. Y.extend(WidgetIO, Y.Plugin.Base, {
  30.  
  31.     // Lifecycle methods.
  32.     initializer: function() {...},
  33.  
  34.     // IO Plugin specific methods
  35.     refresh : function() {...},
  36.  
  37.     // Default IO transaction handlers
  38.     _defSuccessHandler : function(id, o) {...},
  39.     _defFailureHandler : function(id, o) {...},
  40.     _defStartHandler : function(id, o) {...},
  41.     _defCompleteHandler : function(id, o) {...},
  42.     _defFormatter : function(val) {...}
  43. });
/* Widget IO Plugin Constructor */
function WidgetIO(config) {
    WidgetIO.superclass.constructor.apply(this, arguments);
}
 
/* 
 * The namespace for the plugin. This will be the property on the widget, 
 * which will reference the plugin instance, when it's plugged in
 */
WidgetIO.NS = "io";
 
/*
 * The NAME of the WidgetIO class. Used to prefix events generated
 * by the plugin class.
 */
WidgetIO.NAME = "ioPlugin";
 
/*
 * The default set of attributes for the WidgetIO class.
 */
WidgetIO.ATTRS = {
    uri : {...},
    cfg : {...},
    formatter : {...},
    loading: {...}
};
 
/* Extend the base plugin class */
Y.extend(WidgetIO, Y.Plugin.Base, {
 
    // Lifecycle methods.
    initializer: function() {...},
 
    // IO Plugin specific methods
    refresh : function() {...},
 
    // Default IO transaction handlers
    _defSuccessHandler : function(id, o) {...},
    _defFailureHandler : function(id, o) {...},
    _defStartHandler : function(id, o) {...},
    _defCompleteHandler : function(id, o) {...},
    _defFormatter : function(val) {...}
});

Plugin Attributes

The WidgetIO is a fairly simple plugin class. It provides incremental functionality. It does not need to modify the behavior of any methods on the host Widget instance, or monitor any Widget events (unlike the AnimPlugin example).

It sets up the following attributes, which are used to control how the IO plugin's refresh method behaves:

uri
The uri to use for the io request
cfg
The io configuration object, to pass to io when initiating a transaction
formatter
The formatter to use to formatting response data. The default implementation simply passes back the response data passed in, unchanged.
loading
The default content to display while an io transaction is in progress

In terms of code, the attributes for the plugin are set up using the standard ATTRS property:

  1. /* Setup local variable for Y.WidgetStdMod, since we use it 
  2.    multiple times to reference static properties */
  3. var WidgetIO = Y.WidgetIO;
  4.  
  5. ...
  6.  
  7. /* Attribute definition */
  8. WidgetIO.ATTRS = {
  9.     /*
  10.      * The node that will contain the IO content 
  11.      */
  12.     contentNode: {
  13.         value: '.yui3-widget-content',
  14.         setter: '_defContentNodeSetter'
  15.     },
  16.  
  17.     /*
  18.      * The uri to use for the io request
  19.      */
  20.     uri : {
  21.         value:null
  22.     },
  23.  
  24.     /*
  25.      * The io configuration object, to pass to io when initiating 
  26.      * a transaction
  27.      */
  28.     cfg : {
  29.         value:null
  30.     },
  31.  
  32.     /*
  33.      * The default formatter to use when formatting response data. The default
  34.      * implementation simply passes back the response data passed in. 
  35.      */
  36.     formatter : {
  37.         valueFn: function() {
  38.             return this._defFormatter;
  39.         }
  40.     },
  41.  
  42.     /*
  43.      * The default loading indicator to use, when an io transaction is in progress.
  44.      */
  45.     loading: {
  46.         value: '<img class="yui3-loading" width="32px" \ 
  47.                     height="32px" src="assets/img/ajax-loader.gif">'
  48.     }
  49. };
/* Setup local variable for Y.WidgetStdMod, since we use it 
   multiple times to reference static properties */
var WidgetIO = Y.WidgetIO;
 
...
 
/* Attribute definition */
WidgetIO.ATTRS = {
    /*
     * The node that will contain the IO content 
     */
    contentNode: {
        value: '.yui3-widget-content',
        setter: '_defContentNodeSetter'
    },
 
    /*
     * The uri to use for the io request
     */
    uri : {
        value:null
    },
 
    /*
     * The io configuration object, to pass to io when initiating 
     * a transaction
     */
    cfg : {
        value:null
    },
 
    /*
     * The default formatter to use when formatting response data. The default
     * implementation simply passes back the response data passed in. 
     */
    formatter : {
        valueFn: function() {
            return this._defFormatter;
        }
    },
 
    /*
     * The default loading indicator to use, when an io transaction is in progress.
     */
    loading: {
        value: '<img class="yui3-loading" width="32px" \ 
                    height="32px" src="assets/img/ajax-loader.gif">'
    }
};

The formatter attribute uses valueFn to define an instance based default value; pointing to the _defFormatter method on the WidgetIO instance.

Lifecycle Methods: initializer, destructor

Since no special initialization is required, there is no need to implement an initializer method.

The destructor terminates any existing transaction, if active when the plugin is destroyed (unplugged).

  1. initializer: function() {}
  2.  
  3. /*
  4.  * Destruction code. Terminates the activeIO transaction if it exists
  5.  */
  6. destructor : function() {
  7.     if (this._activeIO) {
  8.         Y.io.abort(this._activeIO);
  9.         this._activeIO = null;
  10.     }
  11. },
initializer: function() {}
 
/*
 * Destruction code. Terminates the activeIO transaction if it exists
 */
destructor : function() {
    if (this._activeIO) {
        Y.io.abort(this._activeIO);
        this._activeIO = null;
    }
},

The refresh Method

The refresh method is the main public method which the plugin provides. It's responsible for dispatching the IO request, using the current state of the attributes defined of the plugin. Users will end up invoking the method from the plugin instance attached to the Widget (widget.io.refresh()).

  1. refresh : function() {
  2.     if (!this._activeIO) {
  3.         var uri = this.get("uri");
  4.  
  5.         if (uri) {
  6.             cfg = this.get("cfg") || {};
  7.             cfg.on = cfg.on || {};
  8.  
  9.             cfg.on.start = cfg.on.start || Y.bind(this._defStartHandler, this);
  10.             cfg.on.complete = cfg.on.complete || Y.bind(this._defCompleteHandler, this);
  11.  
  12.             cfg.on.success = cfg.on.success || Y.bind(this._defSuccessHandler, this);
  13.             cfg.on.failure = cfg.on.failure || Y.bind(this._defFailureHandler, this);
  14.  
  15.             cfg.method = cfg.method; // io defaults to "GET" if not defined
  16.  
  17.             Y.io(uri, cfg);
  18.         }
  19.     }
  20. }
refresh : function() {
    if (!this._activeIO) {
        var uri = this.get("uri");
 
        if (uri) {
            cfg = this.get("cfg") || {};
            cfg.on = cfg.on || {};
 
            cfg.on.start = cfg.on.start || Y.bind(this._defStartHandler, this);
            cfg.on.complete = cfg.on.complete || Y.bind(this._defCompleteHandler, this);
 
            cfg.on.success = cfg.on.success || Y.bind(this._defSuccessHandler, this);
            cfg.on.failure = cfg.on.failure || Y.bind(this._defFailureHandler, this);
 
            cfg.method = cfg.method; // io defaults to "GET" if not defined
 
            Y.io(uri, cfg);
        }
    }
}

The refresh method, as implemented for the scope of this example, sets up the io configuration object for the transaction it is about to dispatch, filling in the default handlers for io's start, complete, success and failure events, if the user does not provide custom implementations.

Node Content Helper Method

To simplify implementation and extension, a setContent method is used to wrap the content setter, which by default updates the contentBox of the widget.

  1. /*
  2.  * Helper method for setting host content 
  3.  */
  4. setContent: function(content) {
  5.     this.get('contentNode').setContent(content);
  6. }
/*
 * Helper method for setting host content 
 */
setContent: function(content) {
    this.get('contentNode').setContent(content);
}

The Default IO Event Handlers

The default success listener, pulls the response data from the response object, and uses it to update the content defined by the contentNode attribute, which, by default, is the contentBox. The response data is passed through the formatter configured for the plugin, converting it to the desired output format:

  1. _defSuccessHandler : function(id, o) {
  2.     var response = o.responseXML || o.responseText;
  3.     var formatter = this.get('formatter');
  4.  
  5.     this.setContent(formatter(response));
  6. }
_defSuccessHandler : function(id, o) {
    var response = o.responseXML || o.responseText;
    var formatter = this.get('formatter');
 
    this.setContent(formatter(response));
}

The default failure listener, displays an error message in the currently configured section, when io communication fails:

  1. _defFailureHandler : function(id, o) {
  2.     this.setContent('Failed to retrieve content');
  3. }
_defFailureHandler : function(id, o) {
    this.setContent('Failed to retrieve content');
}

The default start event listener renders the loading content, which remains in place while the transaction is in process, and also stores a reference to the "inprogress" io transaction:

  1. _defStartHandler : function(id, o) {
  2.     this._activeIO = o;
  3.     this.setContent(this.get('loading'));
  4. },
_defStartHandler : function(id, o) {
    this._activeIO = o;
    this.setContent(this.get('loading'));
},

The default complete event listener clears out the "inprogress" io transaction object:

  1. _defCompleteHandler : function(id, o) {
  2.     this._activeIO = null;
  3. }
_defCompleteHandler : function(id, o) {
    this._activeIO = null;
}

Using the Plugin

All objects derived from Base are Plugin Hosts. They provide plug and unplug methods to allow users to add/remove plugins to/from existing instances. They also allow the user to specify the set of plugins to be applied to a new instance, along with their configurations, as part of the constructor arguments.

In this example, we'll create a new instance of a Widget:

  1. /* Create a new Widget instance, with content generated from script */
  2. var widget = new Y.Widget();
/* Create a new Widget instance, with content generated from script */
var widget = new Y.Widget();

And then use the plug method to add the WidgetIO, providing it with a configuration to use when sending out io transactions (The Animation Plugin example shows how you could do the same thing during construction), render the widget, and refresh the plugin to fetch the content.

  1. /*
  2.  * Add the Plugin, and configure it to use a news feed uri 
  3.  */
  4. widget.plug(WidgetIO, {
  5.     uri : 'assets/news.php?query=web+browser',
  6.     loading: '<img class="yui3-loading" width="32px" height="32px" src="assets/img/ajax-loader.gif">'    
  7. });
  8.  
  9. widget.render('#demo');
  10.  
  11. /* fetch the content */
  12. widget.io.refresh();
/*
 * Add the Plugin, and configure it to use a news feed uri 
 */
widget.plug(WidgetIO, {
    uri : 'assets/news.php?query=web+browser',
    loading: '<img class="yui3-loading" width="32px" height="32px" src="assets/img/ajax-loader.gif">'    
});
 
widget.render('#demo');
 
/* fetch the content */
widget.io.refresh();

The plugin class structure described above is captured in this "MyPlugin" Template File, which you can use as a starting point to create your own plugins derived from Plugin.Base.

More Widget Resources:

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