I am trying to establish a PIM listener that will update a MainScreen where all the contacts of the phone are listed.
What I am doing is the following:
I am loading for one time only a form called ContactsForm and I am storing it into the RuntimeStore
I created a PIMListListener to listen for all the changes that will occur in the address book.
When a contact is added, I am adding it to the contactsForm successfully
When a contact is removed, I am facing a big problem deleting it :S!!!
I am getting this exeption: "IllegalArgumentException"; this exception's text is : UiEngine accessed without holding the event lock. I know such errors and I know how to resolve them. So I used the following code:
UiApplication.getUiApplication().invokeLater( new Runnable() { public void run() {
synchronized(UiApplication.getEventLock()) {
uiContacts.vm.delete(uiContacts.vm.getField(j));
}
}});
This should resolve the problem. But I keep getting this error again and again. How to resolve this?
Listeners, like the PIMListListener, do not receive their callbacks in the same Application context as your UiApplication. So, in your code, UiApplication.getUiApplication() doesn't really work the way you'd expect it to.
The best thing to do would be to store a reference to your UiApplication in a place where the callback can reach it (during initialization of the UiApplication, perhaps), and then replace UiApplication.getUiApplication().invokeLater(...) with myUiApp.invokeLater(...), where myUiApp is the reference to your UiApplication which you stored earlier.
Related
Universal App with MVVMLight.
So I started wondering why all the SDK examples were done from code behind rather than using a solid Wrapper class.
So I wanted to write a reusable wrapper class. No luck. Even tried adding that wrapper to a ViewModel, still no luck.
Works fine from MainView.xaml.cs
IBandInfo[] pairedBands = BandClientManager.Instance.GetBandsAsync().Result;
if (pairedBands.Length > 0)
{
using (IBandClient bandClient = await BandClientManager.Instance.ConnectAsync(pairedBands[0]))
{
}
}
The moment I move to any kind of OOP or View Model, ConnectAsync will never return or throw exception. I have tried this 20 different ways, is the SDK broken? What Is happening? No message, no throw, just never returns.
If I throw in Code behind, wallah it works just fine and returns the client in 1/2 second.
I have spend 5-6 hours so far on this. I wanted to create a solid wrapper class for the SDK so I could call easy calls from Model and do things like StartListener(MicrosoftBandSensor sensorToActivate).
Any suggestions?
-- For Phil's comment
I was trying to create backing variables for both client and bandinfo which would be held in a class that the VM uses. I wrote my class as IDisposable so I could dispose of both when I was done with my wrapper. I may be using this wrong to be honest.
MicrosoftBand.MicrosoftBandClient = BandClientManager.Instance.ConnectAsync(pairedBands[0]).Result;
Is what I wanted to call making it a sync call since I wanted to make the calls to bandinfo and client in the constructor then hold both until the class was destroyed and just recall the vars when needed.
My VM has :
public BandInformation MicrosoftBand
{
get { return _microsoftBand; }
set { Set(() => MicrosoftBand, ref _microsoftBand, value); }
}
If they didn't pass the bandclient in the constructor I would use:
private async Task InitBand(IBandInfo bandInfo)
{
if (bandInfo == null)
{
var allBands = await BandClientManager.Instance.GetBandsAsync();
if (allBands.Length > 0)
{
bandInfo = allBands[0];
}
}
var bandClient = await BandClientManager.Instance.ConnectAsync(bandInfo);
MicrosoftBandInfo = bandInfo;
MicrosoftBandClient = bandClient;
if (MicrosoftBandClient == null)
{
AddErrorMessage("This sample app requires a Microsoft Band paired to your device.Also make sure that you have the latest firmware installed on your Band, as provided by the latest Microsoft Health app.");
}
}
This seems fine working with BandInfo. I get back a solid seeming to work object For the client I get "thread exited" and nothing else.
Note: I had it in a try catch throwaway version at one point and nothing threw n exception either.
I assume you can do this like you would any other IDisposable where you handle the disposing yourself.
I can reinstantiate the BandClient each time, just figured I needed to detach the events at some point, meaning I had to keep ahold of the bandclient. I could keep it until done and would add and remove events as I needed each time.
It's likely your blocking call to .Result within your VM constructor is what was causing the hang. IBandClientManager.ConnectAsync() may implicitly display UI (a Windows Runtime dialog asking the user to confirm that she wants to use that specific Bluetooth device). If you've blocked the UI thread when it attempts to display UI, you've now gotten yourself into a deadlock.
Calling Task.Result is almost never a good idea, much less doing so within a constructor where you have little idea on which thread the constructor is executing. If you're working with an async API (such as the Band SDK) then your best bet is to keep that interaction async as well. Instead, defer calling ConnectAsync() until you actually need to, and do so from an async method in your VM. (Deferring the connection is a good idea anyway because you want to minimize the time connected to the Band to preserve battery life.) Then call Dispose() as early as possible to close the Bluetooth connection.
So I went and looked at a bunch of examples. Finally I landed on the GravityHeroUAP demo on the MSDN site. https://msdn.microsoft.com/en-us/magazine/mt573717.aspx?f=255&MSPPError=-2147217396
I looked at his code and the source: https://github.com/kevinash/GravityHeroUWP
He was essentially doing what I wanted to do.
However, I noticed something Bizarre. In his viewmodel everything was static!
public static IBandInfo SelectedBand
{
get { return BandModel._selectedBand; }
set { BandModel._selectedBand = value; }
}
private static IBandClient _bandClient;
public static IBandClient BandClient
{
get { return _bandClient; }
set
{
_bandClient = value;
}
}
I ended up copying this pattern (though had to throw away my favorite MVVM lib in the process, though I am sure I can get it back).
My common pattern in my VM's:
public string ExceptionOnStart {
get { return _exceptionOnStart; }
set { Set(() => ExceptionOnStart, ref _exceptionOnStart, value); }
}
It seems to be working now!
That and I got data way too fast for the
await Windows.Storage.FileIO.AppendLinesAsync(dataFile, new List<string> { toWrite });
Thank you for the help Phil, it got me looking in the right direction!
Thank you very, very much. Spent WAY to long on this. Mark
I'm wondering if anyone has figured out a way to properly handle timeouts in the JavaFX 8 (jdk 1.8.0_31) WebView. The problem is the following:
Consider you have an instance of WebView and you tell it to load a specific URL. Furthermore, you want to process the document once it's loaded, so you attach a listener to the stateProperty of the LoadWorker of the WebEngine powering the web view. However, a certain website times out during loading, which causes the stateProperty to transition into Worker.State.RUNNING and remain stuck there.
The web engine is then completely stuck. I want to implement a system that detects a timeout and cancels the load. To that end, I was thinking of adding a listener to the progressProperty and using some form of Timer. The idea is the following:
We start a load request on the web view. A timeout timer starts running immediately. On every progress update, the timer is reset. If the progress reaches 100%, the timer is invalidated and stopped. However, if the timer finishes (because there are no progress updates in a certain time frame we assume a time out), the load request is cancelled and an error is thrown.
Does anyone know the best way to implement this?
Kind regards
UPDATE
I've produced a code snippet with behavior described in the question. The only thing still troubling me is that I can't cancel the LoadWorker: calling LoadWorker#cancel hangs (the function never returns).
public class TimeOutWebEngine implements Runnable{
private final WebEngine engine = new WebEngine();
private ScheduledExecutorService exec;
private ScheduledFuture<?> future;
private long timeOutPeriod;
private TimeUnit timeOutTimeUnit;
public TimeOutWebEngine() {
engine.getLoadWorker().progressProperty().addListener((ObservableValue<? extends Number> observable, Number oldValue, Number newValue) -> {
if (future != null) future.cancel(false);
if (newValue.doubleValue() < 1.0) scheduleTimer();
else cleanUp();
});
}
public void load(String s, long timeOutPeriod, TimeUnit timeOutTimeUnit){
this.timeOutPeriod = timeOutPeriod;
this.timeOutTimeUnit = timeOutTimeUnit;
exec = Executors.newSingleThreadScheduledExecutor();
engine.load(s);
}
private void scheduleTimer(){
future = exec.schedule(TimeOutWebEngine.this, timeOutPeriod, timeOutTimeUnit);
}
private void cleanUp(){
future = null;
exec.shutdownNow();
}
#Override
public void run() {
System.err.println("TIMED OUT");
// This function call stalls...
// engine.getLoadWorker().cancel();
cleanUp();
}
}
I don't think that you can handle timeouts properly now. Looks at this method. As you can see it has hardcoded value for setReadTimeout method. Is it mean that SocketTimeoutException exception will be raised after one hour of loading site. And state will be changed to FAILED only after that event.
So, you have only one way now: try to hack this problem use Timers as you described above.
P.S.
Try to create issue in JavaFX issue tracker. May be anyone fixed it after 5 years...
I have the same problem and used a simple PauseTransition. Same behavior, not so complicated. =)
I've written a controller and action that I use as a service.
This service runs quite a costly action.
I'd like to limit the access to this action if there is already a currently running action.
Is there any built in way to lock an asp.net mvc action?
Thanks
Are you looking for something like this?
public MyController : Controller
{
private static object Lock = new object();
public ActionResult MyAction()
{
lock (Lock)
{
// do your costly action here
}
}
}
The above will prevent any other threads from executing the action if a thread is currently processing code within the lock block.
Update: here is how this works
Method code is always executed by a thread. On a heavily-loaded server, it is possible for 2 or more different threads to enter and begin executing a method in parallel. According to the question, this is what you want to prevent.
Note how the private Lock object is static. This means it is shared across all instances of your controller. So, even if there are 2 instances of this controller constructed on the heap, both of them share the same Lock object. (The object doesn't even have to be named Lock, you could name it Jerry or Samantha and it would still serve the same purpose.)
Here is what happens. Your processor can only allow 1 thread to enter a section of code at a time. Under normal circumstances, thread A could begin executing a code block, and then thread B could begin executing it. So in theory you can have 2 threads executing the same method (or any block of code) at the same time.
The lock keyword can be used to prevent this. When a thread enters a block of code wrapped in a lock section, it "picks up" the lock object (what is in parenthesis after the lock keyword, a.k.a. Lock, Jerry, or Samantha, which should be marked as a static field). For the duration of time where the locked section is being executed, it "holds onto" the lock object. When the thread exits the locked section, it "gives up" the lock object. From the time the thread picks up the lock object, until it gives up the lock object, all other threads are prevented from entering the locked section of code. In effect, they are "paused" until the currently executing thread gives up the lock object.
So thread A picks up the lock object at the beginning of your MyAction method. Before it gives up the lock object, thread B also tries to execute this method. However, it cannot pick up the lock object because it is already held by thread A. So it waits for thread A to give up the lock object. When it does, thread B then picks up the lock object and begins executing the block of code. When thread B is finished executing the block, it gives up the lock object for the next thread that is delegated to handle this method.
... but I'm not sure if this is what you are looking for...
Using this approach will not necessarily make your code run any faster. It only ensures that a block of code can only be executed by 1 thread at a time. It is usually used for concurrency reasons, not performance reasons. If you can provide more information about your specific problem in the question, there may be a better answer than this one.
Remember that the code I presented above will cause other threads to wait before executing the block. If this is not what you want, and you want the entire action to be "skipped" if it is already being executed by another thread, then use something more like Oshry's answer. You can store this info in cache, session, or any other data storage mechanism.
I prefer to use SemaphoreSlim because it support async operations.
If you need to control the read/write then you can use the ReaderWriterLockSlim.
The following code snip uses the SemaphoreSlim:
public class DemoController : Controller
{
private static readonly SemaphoreSlim ProtectedActionSemaphore =
new SemaphoreSlim(1);
[HttpGet("paction")] //--or post, put, delete...
public IActionResult ProtectedAction()
{
ProtectedActionSemaphore.Wait();
try
{
//--call your protected action here
}
finally
{
ProtectedActionSemaphore.Release();
}
return Ok(); //--or any other response
}
[HttpGet("paction2")] //--or post, put, delete...
public async Task<IActionResult> ProtectedActionAsync()
{
await ProtectedActionSemaphore.WaitAsync();
try
{
//--call your protected action here
}
finally
{
ProtectedActionSemaphore.Release();
}
return Ok(); //--or any other response
}
}
I hope it helps.
Having read and agreed with the above answer I wanted a slightly different solution:
If you want to detect a second call to an action, use Monitor.TryEnter:
if (!Monitor.TryEnter(Lock, new TimeSpan(0)))
{
throw new ServiceBusyException("Locked!");
}
try
{
...
}
finally {
Monitor.Exit(Lock);
}
Use the same static Lock object as detailed by #danludwig
You can create a custom attribute like [UseLock] as per your requirements and put it before your Action
i have suggestions about that.
1- https://github.com/madelson/DistributedLock
system wide lock solution
2- Hangfire BackgroundJob.Enqueue with [DisableConcurrentExecution(1000)] attribute.
Two solution are pending for process to be finished. i don't want to throw error when request same time.
The simplest way to do that would be save to the cache a Boolean value indicating the action is running the required BL already:
if (System.Web.HttpContext.Current.Cache["IsProcessRunning"])
{
System.Web.HttpContext.Current.Cache["IsProcessRunning"] = true;
// run your logic here
System.Web.HttpContext.Current.Cache["IsProcessRunning"] = false
}
Of course you can do this, or something similar, as an attribute as well.
How do i remove or clear the PIMListListeners for a BlackBerryContactList?
I added a Listener like so:
BlackBerryContactList contactList = (BlackBerryContactList)PIM.getInstance().openPIMList(PIM.CONTACT_LIST, PIM.READ_WRITE);
contactList.addListener(new ContactsChangeListener());
So now when i start my app it adds another new listener
You'll probably just need to reboot the device to clear them out.
To keep this from happening again, store a reference to your ContactsChangeListener, and then in your app's onClose() method add a removeListener() call so when the user ends your app it gets cleaned up.
I need to add GPS functionality to an existing Blackberry Application that I've written. I write a stand alone class called CurrentLocation, and include a method to set the various location variables I care about by using the blackberry GPS in conjunction with google's reverse geocoding webservices. Everything is working beautifully, that is, until I try to instantiate my new class in my main application.
No matter what I do, I get a LocationException! .getLocation() doesn't work!
It really confuses me, because if I instantiate my class in a test hello world app, it works just fine.
Are there limits to where you can instantiate classes? I've not encountered any with previous classes I've written. In this case, I'm instantiating my CurrentLocation class in a listener (so the user only makes the lengthy gps and web calls when they want to). I've tried instantiating it in screens, as well. I've tried just gutting the class and using the method call, but that doesn't work either.
Is there something I'm missing entirely here?
http://pastie.org/639545
There's a link to the class I'm making,
And here's the listener I"m trying to instantiate from. I'm in an event thread because I thought it might help (but I get the same exception whether or not I do this).
FieldChangeListener listenerGPS = new FieldChangeListener() {
public void fieldChanged(Field field, int context) {
UiApplication.getUiApplication().invokeLater(new Runnable() {
public void run() {
CurrentLocation loc = new CurrentLocation();
if (loc != null){
country = loc.getCountry();
city = loc.getCity();
state = loc.getState();
road = loc.getRoad();
zip = loc.getZip();
}
}
});
}
};
What am I missing here?
Okay, I got it. Apparently you can't call getLocation() in the eventThread (not just invokeLater, but any listener). So now what I'm doing is getting the coordinates in a thread outside of the event, and worrying about google separately.