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Refreshing a binded property from another Thread doesn't work

In a Xamarin project, I am trying to update a label showed in a loading page.
The loading page contains also an activity indicator control and is showed after the user clicks OK on a display alert and the alert is showed after the user clicks on a button in the UI.
The loading page is necessary because some heavy activity happens in background. Every seconds I query the status of the activity and I want this status be showed on a loading page, giving the user some information about the activity. This activity is wrappred in a ICommand in the ViewModel.
When I run the command I want a variable in the viewModel referred by the page be updated.
The command is executed in a Task.Run method otherwise the loading page is not showed untill the command has done.
This is the code:
View code behind
private async void SelfLearningButton_OnClicked(object sender, EventArgs e)
{
var bindingContext = BindingContext as AutomationViewModel;
if (await DisplayAlert("message",
"OK", "Cancel"))
{
bindingContext.IsLearning = true; //a variable that drives the ISVisibleProperty of the loading page
//Task.Run because the loading page must be showed otherwise I wait for the command to be completed (with async/await too)
_ = Task.Run(() => bindingContext.TheCommand.Execute(null));
}
}
View.xaml
<Label IsVisible="{Binding IsLearning}"
TextColor="#f1c00e"
Padding="0, 20, 0, 0"
HorizontalOptions="CenterAndExpand"
VerticalOptions="FillAndExpand"
FontAttributes="Bold"
x:Name="LearningStatus"
Text="{Binding Status}">
View Model
//The variable that must be updated
public string Status
{
private set
{
if (_status != value)
{
_status = value;
NotifyPropertyChanged();
}
}
get { return _status ; }
}
TheCommand= new Command(
async () =>
{
try
{
int i = 0;
while (i < 10000 )
{
++i;
//Doesn't work
Device.BeginInvokeOnMainThread( ()=> _status= i.ToString()); //sorry for the boxing
}
}
catch(Exception e)
{
//
}
finally
{
IsLearning = false;
}
});
When I run the code of the command the BeginInvokeOnMainThread doesn't update the variable. I use BeginInvokeOnMainThread because view items must be updated in the UI thread. At every iteration _status has the same value used for init it, and setter code of the field is not called. What is going wrong with this code?
Thank you

Why incorrect order of navigation from SplashScreen to MainPage

I trying to understand an example app by Microsoft. Now I can't repeat the next part. The app have classes App and ExtendedSplach. I want to repeat loading by ExtendedSplash. In my case, it's simple switch from splash to main page after some delay.
Introduction
The example to do like this.
If app runs with breakpoints on line .Content = extendedSplash and .Content = rootFrame, then the first will be extendedSplash. But line .Content = extendedSplash the follow after .Content = rootFrame. The constructor ExtendedSplash calls LoadDataAsync that set .Content = rootFram by first.
However, method LoadDataAsync contains await call
await Startup.ConfigureAsync();
I think that thus the first will extendedSplash. And we will see loading page.
class App
...
bool loadState = (e.PreviousExecutionState == ApplicationExecutionState.Terminated);
ExtendedSplash extendedSplash = new ExtendedSplash(e, loadState);
Window.Current.Content = extendedSplash;
Window.Current.Activate();
class ExtendedSplash
public ExtendedSplash(IActivatedEventArgs e, bool loadState)
{
...
LoadDataAsync(this.activatedEventArgs);
}
private async void LoadDataAsync(IActivatedEventArgs e)
{
...
rootFrame.Navigate(typeof(LoginView), shellArgs);
Window.Current.Content = rootFrame;
Window.Current.Activate();
}
Problem
I tried to repeat the same. I want see loading and then swith to other page. But my case with breakpoints looks like the first .Content = rootFrame and the second .Content = extendedSplash. Thus my queue are logo app with delay 5 seconds and then page with extendedSplash. The page rootFrame losing.
I will grateful for any help.
My code
I did the same by App class
bool loadState = (e.PreviousExecutionState == ApplicationExecutionState.Terminated);
ExtendedSplash extendedSplash = new ExtendedSplash(e, loadState);
Window.Current.Content = extendedSplash;
Window.Current.Activate();
And the next by ExtendedSplash
public ExtendedSplash(IActivatedEventArgs e, bool loadState)
{
this.InitializeComponent();
Window.Current.SizeChanged += new WindowSizeChangedEventHandler(ExtendedSplash_OnResize);
this.splashScreen = e.SplashScreen;
this.activatedEventArgs = e;
OnResize();
rootFrame = new Frame();
LoadDataAsync(activatedEventArgs);
}
private async void LoadDataAsync(IActivatedEventArgs e)
{
await Test();
rootFrame.Navigate(typeof(MainPage));
Window.Current.Content = rootFrame;
Window.Current.Activate();
}
private async Task Test()
{
Stopwatch stopwatch = new Stopwatch();
stopwatch.Start();
while (stopwatch.ElapsedMilliseconds < 5000) ;
}

The problem with your code is in fact in the Test() method. You have marked is async, but that doesn't make the method asynchronous. Instead, your code will actually be stuck for five seconds in blocking manner in the while loop.
Try the following version:
private async Task Test()
{
await Task.Delay(5000);
}
This form of code is in fact asynchronous, so as a result the UI thread will be free to display the splash screen in the meantime.
In general - async methods run on the thread that calls them until they hit an "actual" asynchronous code - for example I/O bound async method or when you run your code with await Task.Run(()=>{...}.

UWP Custom Constructor when creating a secondary window

I'm developing a quick application with the sole purpose of using picture-in-picture mode (compact view) in UWP to display Youtube videos over top of my work. Here's the way the current system works:
MainPage - Handles searching of youtube videos
YoutubeItem - A usercontrol that the mainpage creates for each youtube result. Approximately 50 of these are put into a wrap panel.
YoutubeViewer - A seperate page that runs in it's own window and displays the youtube video.
Here's my issue. I store all the information for the youtube video in each of the YoutubeItems. Using a button, I record the click event and handle it. Here's the code for handling the click:
private async void Button_Click(object sender, RoutedEventArgs e)
{
CoreApplicationView newView = CoreApplication.CreateNewView();
int newViewId = 0;
await newView.Dispatcher.RunAsync(CoreDispatcherPriority.Normal, () =>
{
Frame frame = new Frame();
frame.Navigate(typeof(YoutubeViewer), null);
Window.Current.Content = frame;
// You have to activate the window in order to show it later.
Window.Current.Activate();
newViewId = ApplicationView.GetForCurrentView().Id;
});
bool viewShown = await ApplicationViewSwitcher.TryShowAsStandaloneAsync(newViewId);
}
The problem arises when I have to send the link for the video to the YoutubeViewer. Originally, I was doing this through a constructor but upon using this method for the Windows Documentation, I am unable to use my own constructor from my knowledge. How would you folks recommend getting the link to the new window?

There are many ways.
the simplest, though not necessarily the most elegant, is to create a new class that inherits from Frameand add to it a property for the link. Something like this:
public class FooFrame: Frame
{
public string Link;
}
then in your code assign it upon initializing the frame:
FooFrame frame = new FooFrame(){Link = "youtube.link.com"}

Close secondary view completely in UWP

I am using a secondary view to run my media files, but When I close my secondary view with close button on it (while media is still playing) the secondary view/window closes but the media somehow keeps playing because I can hear the sound and source of sound seems to be the primary view (main app window). How can I completely terminate the secondary window when I close it?
Here is my code to create the secondary view.
await CoreApplication.CreateNewView().Dispatcher.RunAsync(CoreDispatcherPriority.Normal, () =>
{
var frame = new Frame();
frame.MinHeight = 200;
frame.MinWidth = 200;
compactViewId = ApplicationView.GetForCurrentView().Id;
frame.Navigate(typeof(CompactNowPlayingPage), caption);
Window.Current.Content = frame;
Window.Current.Activate();
ApplicationView.GetForCurrentView().Title = Title;
});
bool viewShown = await ApplicationViewSwitcher.TryShowAsViewModeAsync(compactViewId, ApplicationViewMode.Default);
Update
After some debugging I've come to know that close button pressed on the secondary view only hides the view but it keeps on running on its thread, I just want that close button to completely close the secondary view, close its thread and destroy the window as a whole.
Update 2
I followed windows samples multiple views and was able to complete all steps, the code runs fine until it reaches Windows.Current.Close() in released event.
Then it gives an exception when it tries "Window.Current.Close()" with in the released event. according to documentation exception occurs due to any on going changes ( which might be because of media file playing ), but I need to force close the window even when media file is playing how can I do that? Here is the exception:
Message = "COM object that has been separated from its underlying RCW cannot be used."
Update 3
This is the latest updated, I am not following official sample now, just following simpler approach now.
Code to open secondary view:
await Helpers.DeviceTypeHelper.CompactOpen(e.ClickedItem as Video, identifier); //where identified is just a string for some custom logic in the secondary view.
//following method is located in a helper class within the project
internal static async Task CompactOpen(Video PlayingVideo, string caption)
{
ApplicationView newView = null;
await CoreApplication.CreateNewView().Dispatcher.RunAsync(CoreDispatcherPriority.Normal, () =>
{
var frame = new Frame();
frame.Navigate(typeof(CompactNowPlayingPage),new object[] { PlayingVideo,caption});
Window.Current.Content = frame;
Window.Current.Activate();
newView = ApplicationView.GetForCurrentView();
newView.Title = PlayingVideo.MyVideoFile.DisplayName;
});
await ApplicationViewSwitcher.TryShowAsStandaloneAsync(newView.Id);
}
Secondary View:
public sealed partial class CompactNowPlayingPage : Page
{
public CompactNowPlayingViewModel ViewModel { get; } = new CompactNowPlayingViewModel();
private CustomMediaTransportControls controls;
public CompactNowPlayingPage()
{
InitializeComponent();
this.Loaded += MediaPage_Loaded;
this.Unloaded += MediaPage_Unloaded;
Microsoft.Toolkit.Uwp.UI.Extensions.ApplicationView.SetExtendViewIntoTitleBar(this, true);
Microsoft.Toolkit.Uwp.UI.Extensions.TitleBar.SetButtonBackgroundColor(this, Colors.Transparent);
}
protected override void OnNavigatedTo(NavigationEventArgs e)
{
string chk = "";
var paramm = e.Parameter as object[];
NowPlayingVideo = paramm[0] as Video;
var vis = Visibility.Collapsed;
chk = paramm[1].ToString();
switch (chk)
{
case "library":
vis = Visibility.Visible;
break;
case "playlist":
vis = Visibility.Visible;
break;
case "history":
vis = Visibility.Collapsed;
break;
case "directplay":
vis = Visibility.Collapsed;
break;
default:
break;
}
controls = new CustomMediaTransportControls(NowPlayingVideo,vis);
Media.TransportControls = controls;
PlayVideo();
}
private Video NowPlayingVideo { get; set; }
private void PlayVideo()
{
if (NowPlayingVideo != null)
{
string token = "";
if (StorageApplicationPermissions.FutureAccessList.Entries.Count == 800)
{
var en = StorageApplicationPermissions.FutureAccessList.Entries;
StorageApplicationPermissions.FutureAccessList.Remove(en.Last().Token);
}
token = StorageApplicationPermissions.FutureAccessList.Add(NowPlayingVideo.MyVideoFile);
Media.Source = null;
Media.Source = $"winrt://{token}";
SetViews();
}
}
private void SetViews()
{
NowPlayingVideo.Views++;
Database.DbHelper.UpdateViews(NowPlayingVideo.MyVideoFile.Path);
}
private void MediaPage_Loaded(object sender, RoutedEventArgs e)
{
Windows.UI.ViewManagement.ApplicationView.GetForCurrentView().Consolidated += MediaPage_Consolidated;
}
private void MediaPage_Unloaded(object sender, RoutedEventArgs e)
{
Windows.UI.ViewManagement.ApplicationView.GetForCurrentView().Consolidated -= MediaPage_Consolidated;
}
private void MediaPage_Consolidated(Windows.UI.ViewManagement.ApplicationView sender, Windows.UI.ViewManagement.ApplicationViewConsolidatedEventArgs args)
{
Window.Current.Close();
}
}
Secondary View XAML:
<Grid Background="{ThemeResource ApplicationPageBackgroundThemeBrush}">
<vlc:MediaElement AreTransportControlsEnabled="True"
Name="Media"
HardwareAcceleration="True"
AutoPlay="True">
</vlc:MediaElement>
</Grid>
Case 1 : Everything runs perfect if I place a video file in Assets folder and give it as a source to the media element and comment the whole OnanvigatdTo method on secondary page. And I am able to successfully close the window as well.
...
Case 2 : But when I try to set the media through the NowPlayingVideo object as shown in the code above and I also use default Transport Controls, so I don't comment the lines used to assign custom transport controls in the above code it runs fine, but when I then try to close the window I get following exception in App.i.g.cs file but stacktrace doesn't exist:
Message = "Attempt has been made to use a COM object that does not have a backing class factory." Message = "COM object that has been separated from its underlying RCW cannot be used.
Case 3 : Exactly like case 2 but here I uncomment Custom transport controls lines so now I am assigning custom transport controls to my media element, this time exception is a bit different with some stacktrace as well
StackTrace = " at System.StubHelpers.StubHelpers.GetCOMIPFromRCW_WinRT(Object objSrc, IntPtr pCPCMD, IntPtr& ppTarget)\r\n at Windows.UI.Xaml.DependencyObject.get_Dispatcher()\r\n at VLC.MediaElement.d__160.MoveNext()\r\n--- End of stack trace ...
Message = "Attempt has been made to use a COM object that does not have a backing class factory."

The short answer is: you need to make sure nothings holds on to your view instance, and you call Window.Close in the view's Consolidated event. The longer answer with code is here in the official sample. Take a look at the ViewLifetimeControl.cs source file: https://github.com/Microsoft/Windows-universal-samples/tree/master/Samples/MultipleViews/cs

C# UWP closing application multiple views

I have a UWP app that dynamically creates another view. But, the problem is when I close the first window, the second still stays on.
With this code I am creating new view:
CoreApplicationView newView = CoreApplication.CreateNewView();
int newViewId = 0;
await newView.Dispatcher.RunAsync(CoreDispatcherPriority.Normal, () =>
{
Frame frame = new Frame();
frame.Navigate(typeof(SecondPage), null);
Window.Current.Content = frame;
// You have to activate the window in order to show it later.
Window.Current.Activate();
newViewId = ApplicationView.GetForCurrentView().Id;
});
bool viewShown = await ApplicationViewSwitcher.TryShowAsStandaloneAsync(newViewId);
How to close the application when user close the first window?

Please refer to Show multiple views for an app.
If secondary views are open, the main view’s window can be hidden – for example, by clicking the close (x) button in the window title bar - but its thread remains active. Calling Close on the main view’s Window causes an InvalidOperationException to occur. (Use Application.Exit to close your app.) If the main view’s thread is terminated, the app closes.
private void Btn_Click(object sender, RoutedEventArgs e)
{
Application.Current.Exit();
}
You could also choose if you want to close the initial window and remove it from the taskbar by specifying the value of ApplicationViewSwitchingOptions.So that there is a single view on your desktop. You just need to close it for closing the application.
private int currentViewId = ApplicationView.GetForCurrentView().Id;
private async void ShowNewView()
{
CoreApplicationView newView = CoreApplication.CreateNewView();
int newViewId = 0;
await newView.Dispatcher.RunAsync(Windows.UI.Core.CoreDispatcherPriority.Normal, () =>
{
Frame frame = new Frame();
frame.Navigate(typeof(SecondPage), null);
Window.Current.Content = frame;
Window.Current.Activate();
newViewId = ApplicationView.GetForCurrentView().Id;
});
await ApplicationViewSwitcher.SwitchAsync(newViewId, currentViewId, ApplicationViewSwitchingOptions.ConsolidateViews);
}