Mairon Croes's List: All things Flex FAQ

• Hello,
   I don’t think Paul’s question was answered and my questions goes in a similar direction.
   Is there a way to get the image data from the FileReference object? Or is there another objet that would allow me to?

   

  The reason is, I would like to covert the image data to a bitearray and send it with other information to AMFPHP as a remote Object.

   

  I’ve been looking around for an example or tutorial that would come close to this but I can’t find one that actually show how to get the user to load (import) the image in my flex app. from a filebrowser like component.

   

  Any help would be greatly appreciated.
   Thanks
   -Alain

  • Question/problem

• Alain,

   

  Similarly, you’d have to use the FileReference object to have the user select a file from their operating system. Next, you would need to upload the file to a server to save the file and then redownload the image and get the image data that way (for the same reasons as above, Flash Player doesn’t allow for immediate data access without sending the data to the server).

   

  You may want to ask the same question on a high traffic list like FlexCoders and see if anybody else has any clever solutions or workarounds.

   

  Peter

  • Answer with no solution

• After researching file upload options in flex, it seems like the only option is through HTTP service requests, such as:
  
  private var fileRef:FileReference;
   ....
   fileRef.upload(new URLRequest(FILE_UPLOAD_URL));
  
  Is there any way to use BlazeDS remote objects to upload a file from Flex interface? Perhaps passing in a FileReference object and marshalling it into an equivalent Java object?

  • Question/Problem
• I know there is a workaround like this. It uses a servlet to upload a file and returns a url. The uploaded file is either stored in session or server file system until the session expires. Use the PropertyProxy to register a custom class which contains this url and convert to java.io.File. It is the limitation of the player. It cannot read the local file system for security reason. There is a sample in blazeds/trunk/qa/apps/qa-regress/WEB-INF/src/blazeds/qa/remotingService/Echo.java
  
  static
       {
           PropertyProxyRegistry registry = PropertyProxyRegistry.getRegistry();
           PropertyProxy proxy = registry.getProxy(java.io.File.class);
           if (proxy == null)
           {
               registry.register(java.io.File.class, new FileProxy());
           }
           proxy = registry.getProxy(FileReference.class);
           if (proxy == null)
           {
               registry.register(FileReference.class, new FileReferenceProxy());
           }
       }
  
  Hope it can help<!--end msg--> 

  • Possible workaround

• We are setting up Builder to launch the help pages into an external browser. The key advantage of which being that the code samples can then be copy/pasted. On a Mac there is a recognised bug in eclipse that if you choose Firefox as the external browser, and it is NOT your normal system default browser. Basically Eclipse attempts to launch a second instance of Firefox which will generate the “Only one copy of Firefox can be open at a time” dialogue…

• Option 2, if you want to keep something else set as your system default browser e.g. Safari, but would use Firefox for displaying Flex Builder help, you need to either edit or create a new external browser entry using a command structure as per comment 5 on the eclipse bug sheet. Essentially the following settings work…

   
   
  • Location: /usr/bin/open
   
  • Parameters: -a firefox %URL%

• When we distribute a reference to an ArrayCollection held by a Proxy and populate view components with that reference, the changes to items in that ArrayCollection are communicated to the various view components it has been made a dataProvider for automagiclly by Flex. 
• When we distribute a reference to an ArrayCollection held by a Proxy and populate view components with that reference, the changes to items in that ArrayCollection are communicated to the various view components it has been made a dataProvider for automagiclly by Flex. 
  
  However when you replace the ArrayCollection instance in the Proxy, no actor with a reference to the previous ArrayCollection is notified.
  
  Ths means your Proxy should send a Notification when it replaces its data object, the ArrayCollection. 
  
  Then, interested Mediators will receive the Notification and replace the previous reference used to populate their view components with the new one.

  • Here Cliff is saying that sending a reference of an ArrayCollection from the proxy to the view makes everything update automagically.
    But when you overwrite or make a new ArrayCollection in the proxy, you need to send a new reference of this ArrayCollection (via notification) to the interested actors.
• It makes sense to take advantage of the tight ArrayCollection (and XMLListCollection) integration with Flex list controls wherever possible just as you have done here. Its just important to remember where the magic happens so that you recognise when to send Notifications and when you can rely on Flex to get display updates happening correctly.

  • Same as above. Use binding as much as possible but remember to send a new reference of the AC when it is overwritten in the proxy.

1 more annotation...

• Do I understand this right: Assume I have a DataGrid in my view component and an object in the Model that has an ArrayCollection object to represent the data.  The view mediator component can retrieve the proxy for the data and obtain the model's ArrayCollection and set the DataGrid's dataProvider property, thus directly binding the model's ArrayCollection to the view's DataGrid for display?
  
  Is that what you meant in this paragraph?  Or should the View in this case actually have another ArrayCollection and when the View mediator receives notifications that the model's data has been updated the mediator should retrieve the contents of the model's ArrayCollection (via the proxy of course) and modify the contents of the view's ArrayCollection to match?

  • Question about using databinding for an arraycollection from the model to the view or make a copy of the collection and use notifications to update the model when the view changes.
• Generally, we want the edits made at the DataGrid (or any visual control) to automatically update the Model, and in turn have other parts of the View informed of such changes if necessary.

  • Answer indicating that it's better to use databinding.
• The reason for simply retrieving the reference from the Proxy and setting it as the dataProvider for the visual control can just be filed under 'playing well with other frameworks'.
  
  That is to say, Flex provides a wonderful solution for updating the data and dependent visual controls when changes happen. The ArrayCollection and XMLListCollections simply do the right thing.
  
  If you happen to be using PureMVC with Flex, it'd be silly to repeat all that effort by adding methods and Notifications in the Proxy that duplicate what Collections are providing. Especially when those classes are going to be compiled into your app anyway if you just use them to hold data.
  

  • Reason for using databinding instead of notifications.

1 more annotation...

• The tecnical reason the update isn't happening is your getter isn't [Bindable] and sending a ChangeEvent. That's purely a Flex thing.
  
  But databinding from the Model to the View is not a good practice. With the MVC pattern, we're trying to separate the Model from the View, and have them communicate in a loosely coupled way. Databinding in the view component to a class in the model means that they are now tightly coupled. The view component cannot be reused without that model class.

  • Hmmm it seems I understood this wrong. Here Cliff is just saying that it's not good practice to bind the model directly in the viewComponent because then the viewComponent would be to tightly coupled to the model. This should be done in the mediator. So data binding from the model to the view is OK but the binding itself must be done in the mediator.

  • Data binding in the model is not good practice!

• In many of the demos I've seen the mediators are directly referencing components [TextInputs for example] within the view. 
  
  Would it be better decoupling to have the view pass the corresponding VO *with* the Event as opposed to having the mediator catch the event, and then "dig into" the view component to "pull out" the desired data (i.e. construct a VO from components w/in the view component)?

  • Question about the correct way of accessing viewComponent properties in the mediator. Send these with an event or access them from mediator?
• The most loosely coupled way is, as you say, to exchange that data using a custom object or VO, passed to the mediator via a custom event.

  • Answer from Cliff, saying that more loose (so sending with event) = better, but may be overkill. It all depends on the complexity of viewComponent.
• But it is best to encapsulate as much of the component’s implementation as possible. Having the component exchange data with a custom typed Object is better.
• If you create a view component that is simple, and it only has one or two properties that the mediator needs access to, then creating a custom event AND a VO is overkill.
• Cliff, would you recommend having the mediator set the currentState property, or having named constants for states and a public function that accepts such a const and uses a switch statement to set the view?

  • Question about setting "currentState" in the mediator.
• I think the Mediator should set the currentState property of the view component to a named constant defined in the view component class.

  • Answer from Cliff to question about setting "currentState" in the mediator.

4 more annotations...