I'm writing a Cocoa app, and I need to indicate to the user that a view is invalid and can't respond until a background job is completed.
Longer version:
A view in my app contains some data fetched from a server. When the app determines that the data is invalid, it fetches fresh information and displays it. Usually the update happens too quickly to see, but if server or network problems cause the background job to take more than a second or two, I need to make sure the user
Cannot interact with the view until the job is finished;
Can tell that the view is awaiting an update; and
Can continue to interact with other parts of the application until the job is finished.
1) is important because any operation initiated with the stale data will fail, and if the network or the server is slow, I don't want the user to waste his time with futile attempts to interact with that part of the application. (It's fine if the user can still see the data. That could conceivably be helpful, actually, but it isn't crucial.)
What is the standard way to do this in Cocoa? For what it's worth, in the Eclipse framework I think I used the showBusy method on ViewPart.
If there isn't a standard way, does anyone have any suggestions for tackling it? I haven't been using OS X very long, so I'm not even sure how an app is supposed to look and behave in this situtaion. (The screenshots on this page looking promising, but it's iOS, not OS X: http://cocoawithlove.com/2009/04/showing-message-over-iphone-keyboard.html)
Right now I'm working on replacing the whole view with an NSProgressIndicator and restoring the view after the task finishes, but removing the view means my app could end up in a funky state if something goes wrong. Also, I'd like to be able to factor this functionality out into its own class or category(?) since I will have this issue with several different view classes in my application. Ideally I'd like to end up with something as simple as Eclipse's view.showBusy(true)/view.showBusy(false).
Any and all help would be appreciated.
Thanks!
Why not just draw another view on top of the busy view? You could either have it display an image that means busy, or draw it as semitransparent, so it shades out the before-update version of the busy view.
Related
I kick off 5 uploads (of varying size) via the BackgroundTransferService. I have the following questions about the way it works:
It seems that on the emulator it does 2 uploads at a time. Is this how it works on the actual device? Can I programmatically change this behavior?
Can I count on the uploads going out in the order that I submitted them? I seem to be getting conflicting results in my testing.
When I inspect the BackgroundTransferService in my application, does it contain requests from other apps as well or just mine?
Do I need to reconnect events for all the BackgroundTransferRequest objects when coming back from being tombstoned? What about coming back from being reactivated?
Do I need to disconnect events from the BackgroundTransferRequest when I remove it from the BackgroundTransferService.Requests collection?
When I try to upload a non-existing URL:Port (on the localhost), the TransferStatus is reported as WaitingForNonVoiceBlockingNetwork. The upload never actually completes/fails. Is this how it is on the device? Should I remove the request when it encounters this TransferStatus?
You cannot influence the behaviour of the BTS. If you don't like the way it works you can write the transfer functionality as part of your own application but then you have to handle running in the background yourself.
There is no guarantee on sequence.
The BTS may be handling requests from other apps but you won't be able to see the details. Requests() will only return details for your app.
Surely a quick test will tell you this.
It's good practice to.
Have you checked the TransferError property whe you reach this situation? This is a perfectly valild status in other situations and so you shouldn't treat this as a automatic fail.
I'm new to Cocoa so apologies if this doesn't make sense.
I'm using an NSBrowser to get a Finder-style column view of some data from a web service.
The NSURLConnection result is returned asynchronously.
My issue is that the browser correctly calls its delegate to populate columns when the app starts, but I can't make it reload once I've got the data.
I've tried reloadDataForRowIndexes, noteHeightOfRowsWithIndexesChanged, addColumn, reloadColumn and loadColumnZero, but none of them trigger the browser to call numberOfRowsInColumn on the delegate as I would expect (and see on startup).
I know the browser delegate is ok because I can see it being called at startup.
Is there another way to ask the browser to refresh, or do I need to try another approach?
Plan B would be to fire the urlConnection off on another thread, and block the browser. I'm not keen on blocking the UI thread as I fear this will cause a beachball.
Plan C maybe would be to delay the browser loading from the nib file until the data was ready, but I'd have a similar issue next node unless I load all nodes a column early in anticipation.
[browser reloadColumn:0] did not work for me but [browser loadColumnZero].
[browser reloadColumn:0] is the right way to go. This just works, no workaround needed. Your error is elsewhere if this does not work for you.
Im pretty new to struts2 and Ajax ,Actually i have a drop down menu in JSP lets say first.jsp, When user select a choice from dropdown menu,I am calling a function of Action class lets say Method1.In this method i am fetching some value from DB(lets say:a,b,c) and one value from java memory lets say d.Then I am forwarding to second.jsp and display all the parameters(a,b,c and d) in tabular format.
Now problem is that the parameter d is dynamic ,this is updating by some other application and if its change then I have to show it on JSP wihout any action.
One solution is I use in second.jsp , so after interval of 10 second again Mehod1 will call and it will fetch value(a,b,c) from db and updated value of d from java memory. and disply it to second.jsp.But in this case i am unnecessary retrieving value from db while my purpose is just to get value d from memory.This is working but this is causing my application to slower.
Can any body suggetst some other solution? or can i do it using ajax and how?
Any other advice? any help is appreciated.try to be more clear, i'm in lack of ideas in this problem, even it sounds like a classic :I have spend hours trying to play around with this but have got nowhere
Okay... What you're asking is a little fuzzy so let me rephrase:
You have a user (USER1) who opens a web page and sees some data.
You have a second user (USER2) (who may be an application) who is able set a value from time to time.
When USER2 updates that value you want USER1 to see it change in their open browser window?
If this is the case you need to understand basic ajax. For that get these demo applications working:
This example uses dojo and perhaps the S2 ajax tag lib I don't remember I prefer not to use ajax tags (as they are deprecated and prefer jquery for ajax):
http://struts.apache.org/2.x/docs/struts-2-spring-2-jpa-ajax.html
This example here shows a very similar application but using jquery, no tag library, upgraded to Spring 3, it still needs polish:
http://www.kenmcwilliams.com/Downloads/
Now that you know how to get data via ajax, look at the request with firebug. You'll see that the request is just like a typical function call, the browser keeps waiting for the data to come back.
What you do is simply not return from the action until new data is provided. This is called long polling see: http://en.wikipedia.org/wiki/Comet_%28programming%29#Ajax_with_long_polling
If you have not written a simple chat program, using just terminal windows I recommend you do so. Two windows per client (client-send, client-receive windows) and you'll need a server program. I remember hacking one together in a few hours using _Thinking In Java 2nd Edition (Later books took out the networking section if I remember correctly). Anyways between understanding client server interaction and long polling will let you get things working. It would be fun to extend the simple terminal based chat application to a S2 ajax chat application. Would make an awesome tutorial! PS: This is just an application of the producer/consumer problem (If you understand that then I guess you don't need to do the fun exercise).
The interfaces would look very pretty if the server was managed by spring. I know there must be nice servers already written but I am not familiar with any, but would love to hear of one.
I'm now writing a Bonjour service listener class, according to the document here:
Currently, it seems working, I can receive "netServiceBrowserWillSearch:" and "didFindService:moreComing:" correctly. However, after a long wait, I cannot receive " netServiceBrowserDidStopSearch:" or "netServiceBrowser:didNotSearch:". Therefore I don't know that is the proper time for my delegate class to stop showing some UI.
Could anyone have an idea for this? Thanks.
NSNetServiceBrowser doesn't stop browsing (and call the -netServiceBrowserDidStopSearch: delegate method) until you explicitly tell it to by calling -stop. After it's found the initial services, it continues informing you as new matching services are added or old ones disappear.
How you handle this depends on how you want your app to behave. If you have a window that continuously shows the available services (e.g. like the Bonjour window in iChat), then it's best to let it continue, and contiuously update the list in response to delegate messages. If you've got more like a dialog that gets populated and then goes away once the user makes a selection (e.g like the system Add Printer... dialog), then you want to keep the browser running while it's displayed, then call -stop once the user dismisses it. If you're waiting to find just one specific service, then you can call -stop once you've found and resolved it.
Vista puts out a new security preventing Session 0 from accessing hardware like the video card, and the user no longer logs into session 0. I know this means that I cannot show the user a GUI, however, does that also mean I can't show one at all? The way my code is set up right now, it would be more work to make it command line only, however if I can use my existing code and just programmatically manage the GUI it would take a lot less code.
Is this possible?
The article from MSDN says this:
• A service attempts to create a user interface (UI), such as a dialog box, in Session 0. Because the user is not running in Session 0, he or she never sees the UI and therefore cannot provide the input that the service is looking for. The service appears to stop functioning because it is waiting for a user response that does not occur.
Which makes me think it is possible to have an automated UI, but someone told me that you couldn't use SendKeys with a service because it was disabled in Session 0.
EDIT: I don't actually need to show the user the GUI
You can show one; it just doesn't show up.
There is a little notification in the taskbar about there being a GUI window and a way to switch to it.
Anyway, there actually is a TerminalServices API command to switch active session that you could call if you really needed it to show up.
You can write a separate process which provides the UI for your service process. The communication between your UI and service process can be done in various ways (search the web for "inter process communication" or "IPC").
Your service can have a GUI. It's simply that no human will ever see it. As the MSDN quote suggests, a service can display a dialog box. The call to MessageBox won't fail; it just won't ever return — there won't be anyone to press its buttons.
I'm not sure what you mean by wanting to "manage the GUI." Do you actually mean pretending to send input to the controls, as with SendInput? I see no reason that it wouldn't be possible; you'd be injecting input into your own program's queue, after all, and SendInput's Vista-specific warnings don't say anything about that. But I think you'd be making things much more complicated than they need to be. Revisit the idea to alter your program to have no UI at all. (That's not the same as having a console program. Consoles are UI.)
Instead of simulating the mouse messages necessary to click a button, for instance, eliminate the middle-man and simply call directly the function that the button-click event would have called.