I am building a compartmentalized Flex application which uses <SWFLoader > to load additional Flex applications inside it. I am currently planning on using the LocalConnection class to have these two applications talk to each other, but I'm wondering if there's any kind of event driven way to have actions in the internal application propagate to the parent application, and/or any way for the parent application to trigger events in the internal application?
yes it can but be careful what types you pass across the bridge if you are loading with loadForCompatability=true. Have a look at this document LoaderInfo paying particular attention to sharedEvents. It basically allows you to raise events from the subApplication to the parent and vice versa. For more complex scenarios, using AIR have a look at the child/parent Sandbox bridges.
Related
I want to use Vaadin Push in my application. I am using vaadin 7.1.2 which has vaadin push built in. I have 2 question:
How to push the changes from the database on change in data in the database? How can I listen to the database changes? Is there any listeners in vaadin push which can be use?
Since I have many modules in my application I want to add push functionality to only selected modules. Is it possible to add push to only selected modules?
Thanks
Abhilash
Abhilash, what kind of persistence layer you are using?
Common Vaadin Container implements PropertySetChangeListener listener so you can register to and receive event for every DB change. But it will work only if you will change DB via this Container.
Well, external changes won't be noticed and no event will be provided. For this case it is a much harder to get noticed about these DB changes. You should implement kind of "middleware", which will handle all DB changes and also it will notify all registered listener.
To second question, I'm not sure what you mean with modules? Could you provide more information with examples?
How to push the changes from the database on change in data in the database? How can I listen to the database changes? Is there any listeners in vaadin push which can be use?
No, no silver bullet there.
Databases do not generally have an event-notification system to alert external systems about changes to the stored data. You need to code such behavior yourself.
Postgres NOTIFY
The Postgres database offers an unusual feature of NOTIFY where a client connected to the database server can be prodded from server-side code such as PL/pgSQL. The server-side code can ship an optional “payload” string to the client. The client-side database-connection implementation must be coded to accept such notifications.
If you have such a client, then you could do something like have triggers that fire when saving changes to certain tables, then use NOTIFY to tickle the client into querying the table name passed as the payload.
This is nowhere near standard SQL, and is a Postgres-specific feature.
Vaadin events
If the only source of changes to the database is within your Vaadin app, you could set up some kind of alert system within your app.
The ServletContext is required by the Servlet spec to represent your web app at runtime. You can get/set “attributes” as a way for the various threads and user sessions to communicate with each other.
You would need a way to track all your user sessions, as discussed here.
Taking a Vaadin-centric approach may not be practical if there is any chance of other sources of changes to the database outside of your app.
For more info on messaging between current Vaadin users, see the Broadcasting to Other Users section in Vaadin docs, as mentioned in this Answer to a similar Question.
Polling
One common solution is polling. Spawn a background thread to query the database, report findings, then sleep. Lather, rinse, repeat. Set the sleep time for the amount of time your users are willing to be out-of-date.
This kind of work is made much easier with a ScheduledExecutorService built into Java SE. Alternatively, Java EE offers an #Schedule annotation as discussed here, but I am unfamiliar with its usage. Either way, you are scheduling a chunk of code to be run repeatedly. By the way, never use the Timer class in a Servlet-based app or Java EE app.
I have used the ScheduledExecutorService successfully in a Vaadin 7 app running in Tomcat 8.5. Learn about the ServletContextListener as a place in your app to launch and shutdown your executor service. See my slides for my talk on the subject.
And be sure to never access the Vaadin user-inteface layouts and widgets from a background thread. Instead, always interact with the UI by calling access or accessSynchronously on the UI class for user-interface related changes or VaadinSession for non-user-interface related changes. Read the Accessing UI from Another Thread section of the Server Push page in Vaadin doc.
Push technology updates
Push technology has been a rapidly evolving field.
As I recall, Vaadin 8 may be much more efficient with Push than Vaadin 7, though I do not recall details. At the very least, Vaadin 8 may be using more recent versions of the Atmosphere library that powers Vaadin Push features. So if possible, you may want to consider migrating to Vaadin 8. Keep in mind that Vaadin 8 has a compatibility layer feature to make it easier for you to bring over Vaadin 7 code.
Most crucial, be sure to use the latest versions of your web container such as Tomcat or Jetty. The support for WebSocket in particular has had significant improvements over the years.
While perhaps not yet ready in practice, the Servlet 4 spec has major implications for the future of Push technology. The spec includes support for HTTP/2 and Request/Response multiplexing to help with server-side push.
Vaadin Push scoped to UI
Since I have many modules in my application I want to add push functionality to only selected modules. Is it possible to add push to only selected modules?
Enabling Push significantly alters your deployment situation, and so you are wise to carefully consider its use.
Vaadin’s support for Push is scoped to your subclass of UI. Your Vaadin app by default has a single UI object for each user, from a single subclass of UI class. But your are free to instantiate additional UI objects within your user’s session. The instances may come from your same UI subclass, or from additional UI subclasses you have authored.
This is precisely how the multi-window/multi-tab support works in Vaadin 7 and Vaadin 8: You instantiate a new UI subclass object and install it into the new web browser window or tab.
I am not sure, but you may be able to swap out a Push-enabled UI object for an alternative non-Push-enabled UI object within the same web browser window/tab. But I have not tried doing so, and I do not know if this is supported or recommended. Personally, I would choose to keep the same UI object installed for the entire life of the window/tab.
what is difference between swfLoader(load application) and ModuleLoader(load module)?
which is better to use?
thanks
The SWFLoader is used to load sub-applications while the ModuleLoader is used to load Modules, as you stated yourself.
The difference is that Modules have a tight link to the application their are loaded in and cannot be used standalone. A subapplication on the other hand really is a separate application that has no direct link to the application it is loaded in. Depending on your use cases, you might consider one or the other.
There is a good stuff available from Adobe here
Be sure to check the section "Comparing loaded applications to modules".
Hi I am new new to flex development.
I am building a flex application which uses rest APIs.
Right now I have created different for different API calls (login, logout, search etc.) And all these services are in main mxml application file.
I am wondering if I can create a separate mxml file like services.mxml that I can use to call any service.
Is this the right approach?
And can you tell me how t do this?
Thanks
Priyank
Yes, you can encapsulate Flex code so it is not all in the same file. Yes, you can also do this with services. In fact the Cairngorm framework uses that exact approach. [And I assume other frameworks do too].
When you create a component architecture the trick is figuring out how components communicate with each other. In Flex, a component can dispatch events to communicate with it's parent. And it can have methods or properties so the parent can communicate with the child.
Encapsulating all services to a single is fine, but you'll need to figure out components will access those services and how those services will send results back to the components. It's not a simple proposition.
I think you need to research the flex component lifecycle a bit and read up on creating Flex Components or ActionScript classes.
Here are a few resources:
http://www.adobe.com/devnet/flex/components.html
http://www.adobe.com/devnet/flex/articles/creating_components.html
http://livedocs.adobe.com/flex/3/html/help.html?content=Part4_CreateComps_1.html
I have a large flex application (the app) running on one server, and many small flex applications (widgets) running on another server, which are to be included in the app so that visually the user see's one continuous application. Due to proprietary third party software, this structure cannot be changed. I am looking for some way to allow the app and the widgets to communicate, allowing the app to make changes to the widgets and the the widgets to notify the app when events are triggered, so that user interaction is fluid and continuous.
There are a few related questions which indicate it's possible to do this by setting up event triggers and listeners. I am wondering if there is any standardized way to do this (the answers aren't very clear) or if anyone has developed a library or API to make this easier.
Something I've had success with is using javascript as a bridge between the swf files. It's a nightmare to debug but it works quite well. Check out the tutorial here for a quick discussion of how to interact with javascript from within flash and vice versa
I assume you are running your Flex apps on a client, not a server; is that correct? You want to swfs from multiple servers to act as single application, correct?
I believe that you can communicate between two swfs using LocalConnection:
http://www.adobe.com/livedocs/flash/9.0/ActionScriptLangRefV3/flash/net/LocalConnection.html
The other questions you link to seem to talk about loading onw swf inside the oher; which is a separate approach.
Use Modules and ModuleLoaders. You'll be able to set the security context, and if you sublcass the Module class and add your own API, you can have a consistent way to communicate with your modules.
Check here for a simple Module:
http://blog.flexexamples.com/2007/08/06/building-a-simple-flex-module/
First, the background:
I am creating a Flex application with a component that displays various dynamically loaded SWFs, one at a time (kind of like a kiosk). These loaded SWFs are created in Flash IDE, not Flex. They will not be created by us (we will provide a .fla template but that's it), so I am loading them into a separate SecurityDomain.
My Questions:
I want the application to be able to call methods inside the loaded SWF. To do this, would I just call Security.allowDomain("domain original app was loaded from") in the startup process for the loaded SWF?
I want the loaded SWF to be able to throw events that are caught by the application. Can I accomplish this through the SWFLoader.swfBridge property?
I am defining an interface for the methods inside the loaded SWF. But, I don't want to leave the implementation up to the customer. Instead, I want to provide another SWF that contains the interface implementation and have it be a constraint that the customer includes it in their SWF. I am not very familiar with the Flash authoring environment, how would it work so that the interface implementation SWF exposes its methods in such a way to be accessible to Flex? Is there a way to sign the SWF so that the Flex application knows that it is dealing with the original, not a spoof? How would the Flex code pass in arguments, since it is across SecurityDomain boundary -- is there marshalling involved (say if I want to pass in a Dictionary or some kind of object graph)?
The Flex application may load hundreds of these smaller other SWFs during its lifetime. How do I make sure it doesn't keep using up more memory? I plan on using SWFLoader.unloadAndStop() and clearing all references in the Flex object that refers to it. Is this enough? Will the AppDomain for the loaded SWF be torn down automatically so that the class definitions are no longer in memory?
Thanks,
Karthik
Some answers:
2) No. Well, you could try, but it would be a mess. You can look into some of the bootstrap loading documentation, but if you're not in complete control of the flash development, this is a lost cause and will end in headache for you.
Depending on your architecture, I would abstract everything out in such a way where communication is happening through javascript or through a localConnection. It might be a pain to use a localConnection to start (giving the serialization size constraints, etc.) but once you get everything hashed out, you won't need to fight with all the security sandbox restrictions. I understand that you want everything to be secure, but if you have control of the server and know where the swfs are being loaded from (and can add numerous layers of security that you invent [for example: having a loaded swf talk to a server when loaded]), you may be better off.
Random thoughts....
Good luck in any case.
Alex Harui from Adobe gave some extremely helpful answers on my post on the Adobe forums. Check them out if you are interested in this same question.
Karthik