Develop Reference

Xamarin/Tizen: Executing Navigation.PopAsync() crashes the app

I have a navigation page that sets up three pages. The first page loads, the user has to pick an option from a listview and then it loads the second page with PushAsync(). At this point the user can now navigate between the three pages by turning the clock face. If I call PopToRootAsync() on the second page it works fine. If the rotary clock face is turned clockwise it loads a third page via PushAsync().
The problem is if I call PopAsync() on that third page OR I change the PopToRootAsync() on the second page to a PopAsync(), the app crashes. I have no way to determine what the error is either as I just get segmentation fault and nothing is written to the Tizen log that is seemingly indicative of why it crashed.
Is there some reason that a PopAsync() would cause this? I know I saw some other articles this could occur if the MainPage is not loaded into a NavigationPage but I'm doing that. I've been looking through stuff and writing debug logs for days but have nothing to show for it. Any help would be more than appreciated. Thank you!
App.cs
public App()
{
MainPage = new NavigationPage(new ServerSelectionPage());
}
ServerSelection.cs
private void ServerSelection_OnItemTapped(object sender, ItemTappedEventArgs args)
{
App.SERVER = (Server)args.Item;
Navigation.PushAsync(new ArrowsPage());
}
PageBase.cs
public async void Rotate(RotaryEventArgs args)
{
Page _currentPage = Page.REMOTE_BUTTONS;
if (this.GetType() == typeof(ButtonsPage))
_currentPage = Page.REMOTE_BUTTONS;
else if (this.GetType() == typeof(ArrowsPage))
_currentPage = Page.REMOTE_ARROWS;
else
_currentPage = Page.SERVER_SELECTION;
// When rotating (previous rotation is ongoing, do nothing)
if (_rotating)
{
return;
}
_rotating = true;
if (!(App.SERVER is null))
{
if (_currentPage == Page.SERVER_SELECTION)
{
if (args.IsClockwise)
await Navigation.PushAsync(new ArrowsPage());
}
else if (_currentPage == Page.REMOTE_DIRECTIONAL)
{
if (args.IsClockwise)
await Navigation.PushAsync(new ButtonsPage());
else
await Navigation.PopToRootAsync();
}
else
{
try
{
if (!args.IsClockwise)
await Navigation.PopAsync(); // This will crash the app
}
catch(Exception ex)
{
Log.Debug(ex.Message);
}
}
}
_rotating = false;
}

After reading the comment by #vin about checking if the Navigation object is null I suddenly had the thought that it may not be the Navigation page but the RotaryFocusObject. So I changed
if (!args.IsClockwise)
await Navigation.PopAsync();
to
if (!args.IsClockwise)
{
RotaryFocusObject = null;
await Task.Delay(300);
await Navigation.PopAsync();
}
and it no longer crashes. The delay is necessary as if you call PopAsync right after setting the object to null it can still sometimes crash.
So apparently if you pop the current page it causes an error as the focus of the rotary dial is still set to the current navigation page. Why this error does not seemingly occur if you use the Navigation.PopToRootAsync() makes no sense to me.

Navigation.PopToRootAsync() and Navigation.PopToRootAsync() are causing destroy of Page renderer, and the Rotate handler is belong to Page Renderer,
If Page renderer was deleted before completion of Rotate Native Callback that is belong to Page renderer, it will be crashed.
await Task.Delay() let to returning native callback.

UWP multiple views not closing

PROBLEM
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?
TRIED
I followed windows samples multiple views and was able to complete all steps, I copied the ViewLifetimeControl.cs file from the sample and used it in my project. the code runs fine until it reaches Windows.Current.Close() in released event of the secondary view.
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? btw here is the exception :
Message = "COM object that has been separated from its underlying RCW cannot be used."
Code to Create and Show secondary view
internal static async Task CompactOpen(string Title, string caption)
{
ViewLifetimeControl viewControl = null;
await CoreApplication.CreateNewView().Dispatcher.RunAsync(CoreDispatcherPriority.Normal, () =>
{
viewControl = ViewLifetimeControl.CreateForCurrentView();
viewControl.Title = Title;
viewControl.StartViewInUse();
var frame = new Frame();
frame.MinHeight = 200;
frame.MinWidth = 200;
frame.Navigate(typeof(CompactNowPlayingPage), new object[] { viewControl,caption});
Window.Current.Content = frame;
Window.Current.Activate();
ApplicationView.GetForCurrentView().Title = viewControl.Title;
});
((App)App.Current).SecondaryViews.Add(viewControl);
var selectedView = viewControl;
var sizePreference = new SizePreferenceString() { Title = "SizePreference", Preference = ViewSizePreference.Default };
var anchorSizePreference = new SizePreferenceString() { Title = "AnchorSizePreference", Preference = ViewSizePreference.Default };
if (selectedView != null && sizePreference != null && anchorSizePreference != null)
{
try
{
selectedView.StartViewInUse();
var viewShown = await ApplicationViewSwitcher.TryShowAsStandaloneAsync(
selectedView.Id,
sizePreference.Preference,
ApplicationView.GetForCurrentView().Id,
anchorSizePreference.Preference);
if (!viewShown)
{
// The window wasn't actually shown, so release the reference to it
// This may trigger the window to be destroyed
}
// Signal that switching has completed and let the view close
selectedView.StopViewInUse();
}
catch (InvalidOperationException)
{
// The view could be in the process of closing, and
// this thread just hasn't updated. As part of being closed,
// this thread will be informed to clean up its list of
// views (see SecondaryViewPage.xaml.cs)
}
}
}
Released Event
private async void ViewLifetimeControl_Released(Object sender, EventArgs e)
{
((ViewLifetimeControl)sender).Released -= ViewLifetimeControl_Released;
// The ViewLifetimeControl object is bound to UI elements on the main thread
// So, the object must be removed from that thread
await mainDispatcher.RunAsync(CoreDispatcherPriority.Normal, () =>
{
((App)App.Current).SecondaryViews.Remove(thisViewControl);
});
// The released event is fired on the thread of the window
// it pertains to.
//
// It's important to make sure no work is scheduled on this thread
// after it starts to close (no data binding changes, no changes to
// XAML, creating new objects in destructors, etc.) since
// that will throw exceptions
Window.Current.Close(); //this is where that exception occurs
}
Note : both of above methods and even all the related variables, all of them I have followed the guidelines within the uwp sample for multiple views.
Thanks in advance, any help would be really appreciated, I only want to force close the secondary view ( If that's possible )

Is this in the editor or the app? If it's in your debug or build of the app, the secondary view is most likely still open but hidden. You may be using a custom close button which doesn't perform its job well enough. Instead of putting down SecondaryViews.Remove you should do what you had originally written and try StopViewInUse. It may not work, I'm not used to this kind of thing.

How to set a "First-Launch-View" in C#

I searched everywhere, but i can't find a tutorial for my problem. I want to set an page to be shown, when the App is launched for the first time. something like th:
First launch:
Greeting.xaml>Setting.xaml>MainPage.xaml
Regular launch goes directly to MainPage.
how can i do this?
I didn't mean a Splashscreen, I mean a page, which is shown only the first time you launch the App, something like a little tutorial.

Your typical template-generated App.xaml.cs has something like this in its OnLaunched method:
if (rootFrame.Content == null)
{
rootFrame.Navigate(typeof(MainPage), e.Arguments);
}
This is where you navigate to your first page. To special-case a first run, do something like this instead:
if (rootFrame.Content == null)
{
IPropertySet roamingProperties = ApplicationData.Current.RoamingSettings.Values;
if (roamingProperties.ContainsKey("HasBeenHereBefore"))
{
// The normal case
rootFrame.Navigate(typeof(MainPage), e.Arguments);
}
else
{
// The first-time case
rootFrame.Navigate(typeof(GreetingsPage), e.Arguments);
roamingProperties["HasBeenHereBefore"] = bool.TrueString; // Doesn't really matter what
}
}
The greetings page should then navigate to your settings page, which should navigate to your main page.
And by using the roaming settings, the user won't see the first-time screen when she logs in to a different machine.

You can set the "first" page within the App.xaml.cs. Search for the OnLaunched void and change rootFrame.Navigate(typeof(MainPage)); to rootFrame.Navigate(typeof(Greeting)); or whtatever you like to call it.
The next step would be to check if the app launches for the first time. You can set an app setting to do that.
1. create the OnnavigatedTo void for your Greeting.xaml (just type "protected override void onna", IntelliSense will suggest it to you) and make is asynchron by inserting "async" after "protected", 2. use this code:
if (ApplicationData.Current.LocalSettings.Values.ContainsKey("isFirstLaunch"))
{
// if that's the first launch, stay, otherwise navigate to Settings.xaml
if (!(bool)ApplicationData.Current.LocalSettings.Values["isFirstLaunch"])
{
await Dispatcher.RunAsync(CoreDispatcherPriority.Normal, () => Frame.Navigate(typeof(Settings)));
}
}
else
{
ApplicationData.Current.LocalSettings.Values["isFirstLaunch"] = false;
}
I haven't tested the code but it should work. If it doesn't, just ask me.
Edit: here's a much better solution :D https://stackoverflow.com/a/35176403/3146261

I just wanted a Disclaimer to be accepted via a MessageBox
IPropertySet roamingProperties = ApplicationData.Current.RoamingSettings.Values;
if (!roamingProperties.ContainsKey("DisclaimerAccepted"))
{
var dialog = new MessageDialog(strings.Disclaimer);
dialog.Title = "Disclaimer";
dialog.Commands.Clear();
dialog.Commands.Add(new UICommand { Label = "Accept", Id = 0 });
dialog.Commands.Add(new UICommand { Label = "Decline", Id = 1 });
var result = await dialog.ShowAsync();
if ((int)result.Id == 1)
Application.Current.Exit();
roamingProperties["DisclaimerAccepted"] = bool.TrueString;
}
I placed it in App.xaml.cs inside of:
if (e.PrelaunchActivated == false)
{
<Inside here>
if (rootFrame.Content == null)
{
}

Visual Studio during Debugging: The function evaluation requires all threads to run

I'm suddenly getting a strange error while debugging. Up to now the variable in the watch windows has been showing correctly. Now I am always getting this error message in the watch windows:
The function evaluation requires all threads to run
I am not able to check any variable anymore. I am not explicitly working with threads. What can I do to get it working again?
I already disabled, as mentioned in some forums, the function: "Enable property Evaluation and other implicit function Calls" in the option window of the debugger. But without success, and it gives me this error:
Error Implicit Function evaluation disabled by the user

From the msdn forum:
This isn't an error in and of itself, but more of a feature of your debugger.
Some properties require code to be executed in order for the property to be read, but if this requires cross-thread interaction, then other threads may have to run as well. The debugger doesn't do this automatically, but certainly can, with your permission.
Just click the little evaluate icon and it will run your code and evaluate the property.
For further details on this behaviour check this excelent article

I ran into this issue when just trying to get items from a table called "AGENCY" using Entity Framework:
var agencies = db.AGENCY.OrderBy(e => e.FULLNAME);
Hovering over agencies in debug mode, clicking to expand the options, and clicking Results would give the dreaded "The function evaluation requires all threads to run" with a "Do Not Enter" icon at the end that, on which, clicking did nothing.
2 possible solutions:
Add .ToList() at the end:
var agencies = db.AGENCY_TABLE.OrderBy(e => e.FULLNAME).ToList();
List<AGENCY_TABLE> agencies = db.AGENCY_TABLE.OrderBy(e => e.FULLNAME).ToList();
Credit goes to Hp93 for helping me come to this solution. In the comments on MUG4N's answer where I found this solution, it also mentions trying .Any() instead of .ToList(), but this gives a Boolean instead of a <T>, like <AGENCY> is, so it probably wouldn't help.
Workaround - try a different path in the debug options. I found that I could click on the "Non-Public Members" > "_internalQuery" > ObjectQuery > Results View and get my values that way.

MUG4N has indeed provided a correct answer however if you hover over the line of code in debug, you may be looking at something like the below. If so, click the little re-evaluate icon highlighted in the image below...
NB: I obtained this image by pinning, normally the re-evaluate icone are in the middle of the window and not down the left hand column.

You should make thread safe call because accessing Windows form controls are not Thread safe in multithreading.
This is my simple code which makes Thread safe call and sets Progress bar.
public partial class Form1 : Form
{// This delegate enables asynchronous calls for setting
// the text property on a TextBox control.
delegate void StringArgReturningVoidDelegate(string text);
private Thread demoThread = null;
public int Progresscount = 0;
static EventWaitHandle waithandler = new AutoResetEvent(false);
public Form1()
{
InitializeComponent();
}
public static bool CheckForInternetConnection()
{
try
{
using (var client = new WebClient())
{
using (var stream = client.OpenRead("http://www.google.com"))
{
return true;
}
}
}
catch
{
return false;
}
}
public void Progressincrement()
{
waithandler.WaitOne();
while (CheckForInternetConnection()==true)
{
if (Progresscount==100)
{
break;
}
SetLabel("Connected");
Progresscount += 1;
SetProgress(Progresscount.ToString());
Thread.Sleep(TimeSpan.FromSeconds(1));
}
if (Progresscount <100)
{
Startthread();
}
SetLabel("Completed");
}
public void Startthread ()
{
this.demoThread= new Thread(new ThreadStart(Progressincrement));
this.demoThread.Start();
SetLabel("Waiting for connection");
while (CheckForInternetConnection() == false) ;
waithandler.Set();
}
private void SetLabel(string text)
{
// InvokeRequired required compares the thread ID of the
// calling thread to the thread ID of the creating thread.
// If these threads are different, it returns true.
if (this.label1.InvokeRequired)
{
StringArgReturningVoidDelegate d = new StringArgReturningVoidDelegate(SetLabel);
this.Invoke(d, new object[] { text });
}
else
{
this.label1.Text = text;
}
}
private void SetProgress(string Value)
{
// InvokeRequired required compares the thread ID of the
// calling thread to the thread ID of the creating thread.
// If these threads are different, it returns true.
if (this.progressBar1.InvokeRequired)
{
StringArgReturningVoidDelegate d = new StringArgReturningVoidDelegate(SetProgress);
this.Invoke(d, new object[] {Value});
}
else
{
this.progressBar1.Value = Convert.ToInt32(Value);
}
}
private void Form1_Load(object sender, EventArgs e)
{
Startthread();
}
private void button1_Click(object sender, EventArgs e)
{
MessageBox.Show("Responsive");
}
}
For more information MSDN

This isn't an error, but more of a feature of your debugger.
The debugger doesn't do this automatically, but certainly can, with users permission. Just click the little space icon and it will run the code and evaluate the property.

I use the next workaround to pass:
var OtherThreadField = "";
Invoke(new MethodInvoker(delegate
{
OtherThreadField = ExecuteNeededMEthod();
}));
Now i have a value for OtherThreadField.

I faced the same issue and solved .The Issue arise due to username and password ,in SQL connection there is user and password but in code there no user and password. so I enable the user and the password and the issue solved

For me, this happened when trying to break on a line that accesses a complex object instance contained by a Settings Class.
A breakpoint on the following if results in Settings.Default.FindSettings with the value being "The function evaluation requires all threads to run." If I press the force eval button, it is null. Stepping with the force eval button click or not enters the if block and initializes the object. If I remove the breakpoint and add a new breakpoint following the if block, the Settings.Default.FindSettings deserializes properly with the expected values.
if (Settings.Default.FindSettings == null)
{
Settings.Default.FindSettings = new FindSettings();
}
After trial and error, I added the following code before the above if block to access the settings prior to breaking. This seems to reliably fix the problem. I do not need it in production so I wrap in conditional compiler directive. I have a comment in the code instead of a non-descript discard:
#if DEBUG
var _ = Settings.Default.FindSettings;
#endif
I am not sure if the above line would be optimized out in production since it has side effects. As I only need it while debugging, I have not checked.

C#/XAML App Lifecycle - Jump login page after Terminating app

In my Windows Store App i've followed the Microsoft guidelines to resume the app after it is terminated(http://goo.gl/oZ7BG).
It all works but after the app is terminated i'd like to jump the login page(that is the first page in the app) and go directly to the Menu page of the app. It's absolutely like the Dropbox app. I know i have to work to the App.xaml.cs and this method:
protected async override void OnLaunched(LaunchActivatedEventArgs args)
{
Frame rootFrame = Window.Current.Content as Frame;
// Do not repeat app initialization when the Window already has content,
// just ensure that the window is active
bool appTerminated = false;
if (rootFrame == null)
{
// Create a Frame to act as the navigation context and navigate to the first page
rootFrame = new Frame();
marketingHP.Common.SuspensionManager.RegisterFrame(rootFrame, "appFrame");
if (args.PreviousExecutionState == ApplicationExecutionState.Terminated)
{
//TODO: Load state from previously suspended application
await marketingHP.Common.SuspensionManager.RestoreAsync();
appTerminated = true;
}
// Place the frame in the current Window
Window.Current.Content = rootFrame;
}
if (rootFrame.Content == null)
{
// When the navigation stack isn't restored navigate to the first page,
// configuring the new page by passing required information as a navigation
// parameter
if (appTerminated)
rootFrame.Navigate(typeof(HomePage), args.Arguments);
else if (!rootFrame.Navigate(typeof(LoginPage), args.Arguments))
{
throw new Exception("Failed to create initial page");
}
}
// Ensure the current window is active
Window.Current.Activate();
}
How can i understand that the app is terminated before?
Note that i've added the bool appTerminated but it works only for suspending...

Read up further on windows 8 app lifecycle here:
http://msdn.microsoft.com/en-us/library/windows/apps/hh464925.aspx
Particularly, notice the section regarding the PreviousExecutionState property and the table included there outlining the different terminated states. It seems like what you would want to do is check the value of PreviousExecutionState, and if that value reflects the condition in which you want to skip the login page (e.g. the user has already logged in), then you should navigate to your homepage, similar to what you've tried to do above.
If you are closing the app manually and windows is not terminating it due to resource constraints, or it was closed unexpectedly, then appTerminated won't be set to true.
Instead of:
if (args.PreviousExecutionState == ApplicationExecutionState.Terminated)
Include a check to see if the app was terminated by the user:
if (args.PreviousExecutionState == ApplicationExecutionState.Terminated ||
args.PreviousExecutionState == ApplicationExecutionState.ClosedByUser)
This will catch both when windows terminates the app due to resource constraints and when a user terminates the app manually. Then, on startup from termination, appTerminated should be set to true, and the app should navigate directly to HomePage.
edit:
In answer to your comment, what you could do is inside the App.xaml file, provide logic that changes the arguments passed in the Navigate call. You could do something like this:
string navArgs = "FromApp";
if (appTerminated)
{
navArgs = "FromTerminated";
}
Then, just pass this to HomePage when you call Navigate:
if (appTerminated)
{
rootFrame.Navigate(typeof(HomePage), navArgs);
}
Now, in your HomePage code behind file, define the OnNavigatedTo method. This takes a NavigatedEventArgs that you can then cast as some object (in this case as a String) and then check to see what was passed:
protected override void OnNavigatedTo(NavigationEventArgs e)
{
string navArgs = e.Parameter as String;
switch (navArgs)
{
case "FromApp":
//Do something here
break;
case "FromTerminated":
//Do something different here
break;
default:
break;
}
}
Hope this helps!