Part 1 – Frameworks
Part 2 – Directory structure
Part 3 – Application and ApplicationFacade
Part 4 – Notifications, Commands & Use Cases
Part 5 – Model & Proxy
Part 6 – The Application View & Mediator
Part 7 – The Login View & Mediator
Part 8 – The Roster View & Mediator
Part 9 – The Chat View & Mediator
Conclusion, Demo & Downloads
In this part of the tutorial we’ll create the login bar, and by the end of this section our application will be able to connect to any XMPP server with a username & password!
In the components package create a new MXML file name LoginView.mxml and in the view package create a new mediator called LoginMediator.as using Add->New Mediator… (if you don’t see this menu item be sure you’ve installed the PureMVC FlashDevelop templates from PureMVC: First thoughts & FlashDevelop templates correctly).
As we explained in the previous section add a helper method to the LoginMediator to cast the viewComponent:
Note that in order to get the application to compile you’ll need to explicitly import the LoginView using:
Now we want to add the LoginView to the display list by including it in Application.mxml (giving it an id of loginView so we can reference it from the mediator). Add this MXML within the <mx:Application> tag (stick it at the end just before </mx:Application>):
Now we need to register our mediator with PureMVC. Now this point is important to understand as it seems to confuse – since LoginView is a sub-component of Application we need to register the view within the Application’s mediator. This can be made into a general rule:
- If the mediator you are registering heralds the top level component (i.e. Application.mxml) register it in StartupCommand.
- If the mediator you are registering heralds a child of another component register it in the constructor of that component’s mediator.
Just to confuse things I’d better point out that this rule doesn’t apply in quite the same way if you are dynamically creating and removing mediators, but we’ll save that for another tutorial.
Anyway, the upshot of all that is that we call registerMediator in the constructor of ApplicationMediator:
Here is the code for LoginView.mxml. As this is a PureMVC tutorial, not a Flex one, I’m not going to go in any detail about how it works, but these are the only things you need to care about:
- When the user clicks ‘Connect’ it dispatches a LoginViewEvent.LOGIN event containing the username, password and server.
- When the user clicks ‘DIsconnect’ it dispatches a LoginViewEvent.LOGOUT event.
- It exposes a showInvalidLoginAlert() method that pops up a ‘Invalid username/password’ window.
We’ll also need to create the custom LoginViewEvent (in the events folder):
Now we’re ready to start the interesting bit – implementing our LoginMediator. These are the steps I take when implementing a mediator:
- Add listeners for all the events dispatched from the view component to the constructor and create event listener methods for them.
- Identify which notifications this mediator is interested in and add them to the listNotificationInterests method’s array and the handleNotification method’s switch statement.
- Fill in the event listener methods and switch statement clauses.
Now we’ll do each of these steps in turn for our LoginMediator.
1. Add listeners
Our view component dispatches LoginViewEvent.LOGIN and LoginViewEvent.LOGOUT event, so we’ll add our listeners in the constructor and add two empty event listener methods:
2. Add notifications
The login view is interest in knowing if a client is connected or not (so that it can enable/disable the ‘Connect’ & ‘Disconnect’ buttons accordingly. It is also interested in knowing if a login attempt was invalid so that it can popup the ‘Invalid username/password’ alert. This translates into listening for ApplicationFacade.VALID_LOGIN, ApplicationFacade.INVALID_LOGIN and ApplicationFacade.DISCONNECT.
Firstly we’ll add these to the listNotificationInterests method:
Now we’ll add empty clauses for each notification in the handleNotification method’s switch statement:
3. Fill in the event listeners and switch clauses
Let do the switch clauses first. Its all simple stuff – in the event of a valid login we want to enable the ‘Disconnect’ button and disable the ‘Connect’ button, in the event of a disconnect we want to enable the ‘Connect’ button and disable the ‘Disconnect’ button, and in the event of an invalid login we want to popup the ‘Invalid username/password’ alert box:
And now lets fill in our event listeners. Again, these are very simple – all they do is send the appropriate notification which will then get auto-mapped to the appropriate command – in this case either LoginCommand or LogoutCommand.
Notice that for the parameter of the notifications I am just passing the same LoginViewEvent we received from the view component. It could be argued that this breaks encapsulation as the commands shouldn’t really know anything about events. However, after coding a few PureMVC projects I’ve noticed that its very common for the event you receive from the view to contain the same bits of information needed by the relevant command – in this case LoginCommand needs to know the username, password and server which is exactly the information contained in a LoginViewEvent. Because of this I don’t really see the need to create an extra object, and when passing an event as notification parameter I just think of it as a value object instead of an event, but you are certainly justified in taking another view on this.
Now that we have the mediator calling the LoginCommand and LogoutCommand we’d better fill these in. Commands can do various different things, but a very common pattern for commands, and what we’ll be using here, is:
- Retrieve the proxy we want to do something with using retrieveProxy.
- Call a method on that proxy, possibly with parameters ripped out of the notification parameter.
With that in mind we can very simply implement LoginCommand.as:
… and LogoutCommand.as:
Guess what? We have a working application! Compile the application and play about with it – you’ll be able to log in and out of Jabber servers to your heart’s content 🙂 If you download a proper jabber client (http://www.jabber.org/clients has a big list of clients for various platforms) you’ll be able to see your user coming on and offline as you click ‘Connect’ and ‘Disconnect’.
Be proud! All that’s left for us to do now is to create a buddy list (called the Roster in Jabber parlance) and the chat windows themselves. If you’ve come this far maybe you’d like to have a go yourself without reading further. If not, read on – Roster view here we come.