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Create MVC-model-view-controller component for joomla 1.5 - Hello World 02
Introduction:
I descibed my first "helloworld component for joomla 1.5 in my previous tutorial
hello world component for joomla 1.5 I have got a huge response for joomla developers and I believe some of them were right pointing out
that helloworld should be rewritten in MVC framework.
This is very brief introduction. Please refer to these links for thorough explanation.
MVC - model view controller
MVC is an architectural pattern used in software engineering. In
complex computer applications that present lots of data to the user,
one often wishes to separate data (model) and user interface (view)
concerns, so that changes to the user interface do not impact the data
handling, and that the data can be reorganized without changing the
user interface. The model-view-controller solves this problem by
decoupling data access and business logic from data presentation and
user interaction, by introducing an intermediate component: the
controller.
After researching various articles on the internet I came up with the following descriptions of the principles of the Model-View-Controller design pattern:
The MVC paradigm is a way of breaking an application, or even just a piece of an application's interface, into three parts:
the model, the view, and the controller.
MVC was originally developed to map the traditional input, processing, output roles into the GUI realm:
Input --> Processing --> Output
Controller --> Model --> View
Model
The model is the part of the component that encapsulates the
application's data. It will often provide routines to manage and
manipulate this data in a meaningful way in addition to routines that
retrieve the data from the model. In our case, the model will contain
methods to add, remove and update information about the books in the
database. It will also contain methods to retrieve the list of books
from the database. In general, the underlying data access technique
should be encapsulated in the model. In this way, if an application is
to be moved from a system that utilizes a flat file to store its
information to a system that uses a database, the model is the only
element that needs to be changed, not the view or the controller.
View
The view is the part of the component that is used to render the
data from the model in a manner that is suitable for interaction. For a
web-based application, the view would generally be an HTML page that is
returned to the data. The view pulls data from the model (which is
passed to it from the controller) and feeds the data into a template
which is populated and presented to the user. The view does not cause
the data to be modified in any way, it only displays data retrieved
from the model.
Controller
The controller is responsible for responding to user actions. In the
case of a web application, a user action is a page request. The
controller will determine what request is being made by the user and
respond appropriately by triggering the model to manipulate the data
appropriately and passing the model into the view. The controller does
not display the data in the model, it only triggers methods in the
model which modify the data.
Joomla! MVC Implementation
In Joomla!, the MVC pattern is implemented using three classes:
- JModel
- JView
- and JController
Hello world component
a) structure
│ com_helloworld.xml (xml - installation source)
│
├───admin - (administration folder)
│ │ index.html - (blank file)
│ │ admin.helloworld.php - (create controller and hand over the control)
│ │ toolbar.helloworld.php - (tool bar definition and a 'help' menu item)
│ │ toolbar.helloworld.html.php - (tool bar definition and a 'help' menu item)
│ │
│ ├───images - (here are all picures used in the component)
│ │ helloworld.png
│ │ index.html - (blank file)
│ │
│ ├───controllers - (controlers folder)
│ │ default.php - (default controler - "default section")
│ │ helloagain.php - (heloagain controler - "helloagain section")
│ │ hellotestfoo.php - (hellotestfoo controler - "helhellotestfooloagain sec.")
│ │ helloworld.php - (helloworld controler - "helloworld section")
│ │
│ ├───models - (models folder)
│ │ helloworld.php - (the only model defined here. Currently not in use)
│ │
│ ├───views - (views folder)
│ │ ├───default
│ │ │ view.php - (default view - "default section")
│ │ │
│ │ ├───helloagain
│ │ │ view.php - (helloagain view - "helloagain section")
│ │ │
│ │ ├───hellotestfoo
│ │ │ view.php - (hellotestfoo view - "hellotestfoo section")
│ │ │
│ │ └───helloworld
│ │ view.php - (helloworld view - "helloworld section")
│ │
│ ├───sql - (SQL folder. Currently not in use. All sql files)
│ │ uninstall.helloworld.sql ( are commented out in the installation xml.)
│ │ install.helloworld.sql ( The reasson is very simple. Joomla! 1.5 has )
│ │ ( a minor bug in installation.php. We will need )
│ │ ( a "night build" for the next tutorial)
│ │
│ └───lang - (language folder)
│ cs-CZ.com_helloworld.ini - (czech text package)
│ en-GB.com_helloworld.ini - (english text package)
│
└───component
│ index.html - (blank file)
│ helloworld.php - (core for the frontend application. )
│ ( Prints "hello world".)
└───lang
cs-CZ.com_helloworld.ini - (czech text package)
en-GB.com_helloworld.ini - (english text package)
b) concept
We need to rewrite the core of our previous component.
It prints "hello world" by accessing methods of class helloScreens in
admin.helloworld.html.php
class helloScreens
{
function helloworld()
{ echo JText::_('helloworld'); }
function helloagain()
{ echo JText::_('helloagain'); }
function hellotestfoo()
{ echo JText::_('hellotestfoo'); }
function hellodefault()
{ echo JText::_('hellodefault'); }
}
All these methods will become stand-alone views.
\views\helloworld\view.php
class HelloWorldComponentView extends JView
{
function display()
{
echo JText::_('helloworld');
}
}
As you can see there is no model instance passing into the view or accessing from the view.
Unfortunatelly, there is a minor bug in joomla1.5 beta that prevents us from executing
our sql script in the installation process. We can get around this problem by installing jomla 1.5 "night build"
and I will show you how in the next joomla tutorial.
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Joomla 1.5 
