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.

Bring the UWP app to the front of current window

How can i use
await Windows.System.Launcher.LaunchUriAsync(new Uri("protocol://"));
to navigate to specific view of uwp application.
Is there any way to bring the app in front of the screen, if app was minimized or hidden behind other apps?
Thanks in advance

How can i use await Windows.System.Launcher.LaunchUriAsync(new Uri("protocol://")); to navigate to specific view of uwp application
For this, firstly you need to add the Protocol declaration in your Package.appxmanifest file . (Go to declarations tab and add Protocol from the available protocols). ( MSDN Doc )
Here i am using "app-protocol" as the protocol name.
Once this is done, you need to override the OnActivated() method in your App.xaml.cs. This method will be called when the app is launched using the protocol.
The arguments that we pass when calling the protocol can be retrieved here and based on that you can show your page or maybe pass that parameter to your page and let it handle the navigation .
For instance, if our Uri is app-protocol:login?param1=true, when you receive the ProtocolActivatedEventArgs eventArgs in the onActivated() method you will have access to the whole Uri.
You can use eventArgs.Uri to access all the Uri properties.
In any case your code should look something like this :
C#
protected override void OnActivated(IActivatedEventArgs args)
{
if (args.Kind == ActivationKind.Protocol)
{
ProtocolActivatedEventArgs eventArgs = args as ProtocolActivatedEventArgs;
// Get the root frame
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
if (rootFrame == null)
{
// Create a Frame to act as the navigation context and navigate to the first page
rootFrame = new Frame();
rootFrame.NavigationFailed += OnNavigationFailed;
if (args.PreviousExecutionState == ApplicationExecutionState.Terminated)
{
//TODO: Load state from previously suspended application
}
// Place the frame in the current Window
Window.Current.Content = rootFrame;
}
//URI : app-protocol:login?param1=true
//Logic for showing different pages/views based on parameters passed
if (eventArgs.Uri.PathAndQuery != string.Empty)//PathAndQuery:login?param1=true
{
var absolutePath = eventArgs.Uri.AbsolutePath;//AbsolutePath:login
if (absolutePath.Equals("login"))
{
rootFrame.Navigate(typeof(LoginPage));
}
else
{
rootFrame.Navigate(typeof(MainPage));
}
}
else
{
rootFrame.Navigate(typeof(MainPage));
}
}
// Ensure the current window is active
Window.Current.Activate();
}
Is there any way to bring the app in front of the screen, if app was minimized or hidden behind other apps?
We are calling Window.Current.Activate(); to ensure this.

To bring any UWP window to the front use this snippet (works if window with given viewId was already created and is either minimized or behind other windows:
private async Task TryActivateViewAsync(viewId)
{
if (Window.Current.Dispatcher != null)
{
await Window.Current.Dispatcher.RunAsync(CoreDispatcherPriority.Normal, async () =>
{
if (await ApplicationViewSwitcher.TryShowAsStandaloneAsync(viewId))
{
await ApplicationViewSwitcher.SwitchAsync(viewId);
}
});
}
}
Just as a reminder, viewId is an Identifier of a window which you can get when you create that window using:
var coreView = CoreApplication.CreateNewView(); // creates new view
await coreView.Dispatcher.RunAsync(CoreDispatcherPriority.Normal, () =>
{
_someViewId = ApplicationView.GetForCurrentView().Id; // gets that view's id
}

Windows Phone 8.1 check if password set else load new page

I Have a very similar situation to this guys question in that I have a Login Page which is my MainPage.xaml file but I have another page called SetPassword.xaml that I want to load if a user has not set a password yet. Essentially this is the first time that the App loads after it has been installed.
I've spent hours on SO trying various different solutions (including the one I linked to) but I'm just not getting anywhere and it seems that many of the solutions are either for WP7 or WP8 and nothing similar has been solved for the new WP8.1.
This is the basic check, using Windows.Storage that I'm doing to see if a password has been set or not.
Windows.Storage.ApplicationDataContainer localSettings = Windows.Storage.ApplicationData.Current.LocalSettings;
Windows.Storage.StorageFolder localFolder = Windows.Storage.ApplicationData.Current.LocalFolder;
if (localSettings.Values["myPassword"] == null)
{
Debug.WriteLine("Password not set");
this.Frame.Navigate(typeof(SetPassword));
}
else
{
Debug.WriteLine("Password is set, continuing as normal");
}
If I add this to public MainPage() class I have no problem in the app returning "Password is not set" in the debug messages however the this.frame.Navigate(typeof(SetPassword)) navigation never loads the SetPassword view.
I have also tried this method in the OnNavigatedTo with exactly the same results.
In my App.xaml file I've also tried a number of different methods, again, with the same results. I can get the debug message but not the navigation I'm looking for. I looked at implementing a method on Application_Launching over here as well as implementing conditional navigation on RootFrame.Navigating+= RootFrameOnNavigating; over here but clearly I am missing something.
Hopefully you smarter people can help me get my navigation working based on a conditional value?

The solution was simple. To do the navigation I could have done it in either App or MainPage as per my question but the reason the navigation wasn't working was because I was trying to navigate to SetPassword.xaml which was a <ContentDialog> instead of a <Page>.
I feel embarrassed actually that I didn't even check that but hopefully if this happens to someone else they can check that they're actually trying to navigate to a Page and not any other type of element. How sadly foolish of me!
EDIT:
Here's what my OnLaunched in the App.xaml file looks like where I can now do my check and redirect to a different page based on the value being set.
protected override void OnLaunched(LaunchActivatedEventArgs e)
{
Frame rootFrame = Window.Current.Content as Frame;
if (rootFrame == null)
{
rootFrame = new Frame();
rootFrame.CacheSize = 1;
Window.Current.Content = rootFrame;
// The following checks to see if the value of the password is set and if it is not it redirects to the save password page - else it loads the main page.
Windows.Storage.ApplicationDataContainer localSettings = Windows.Storage.ApplicationData.Current.LocalSettings;
Windows.Storage.StorageFolder localFolder = Windows.Storage.ApplicationData.Current.LocalFolder;
if (localSettings.Values["myPassword"] == null)
{
rootFrame.Navigate(typeof(SetPassword));
}
else
{
rootFrame.Navigate(typeof(MainPage));
}
}
if (rootFrame.Content == null)
{
if (rootFrame.ContentTransitions != null)
{
this.transitions = new TransitionCollection();
foreach (var c in rootFrame.ContentTransitions)
{
this.transitions.Add(c);
}
}
rootFrame.ContentTransitions = null;
rootFrame.Navigated += this.RootFrame_FirstNavigated;
if (!rootFrame.Navigate(typeof(MainPage), e.Arguments))
{
throw new Exception("Failed to create initial page");
}
}
Window.Current.Activate();
}

WP8: Fast app resume + secondary tile + MainPage = 2 instances

I'm having the same problem posed here:
http://social.msdn.microsoft.com/Forums/wpapps/en-us/af8615e7-8e90-4069-aa4d-3c4a84a6a3d0/windows-phone-8-fast-app-resume-with-deeplinks?forum=wpdevelop
I'm no C# or WP expert, so please bear with me.
I have secondary tiles which link to "/MainPage.xaml?id=XX".
I have fast app resume enabled. (ActivationPolicy="Resume" in the app manifest)
I only have one page in my app: MainPage.xaml.
Problem: When I resume the app using a secondary tile ("/MainPage.xaml?id=XX"), I get a brief view of the previous instance (that would have resumed) and then the MainPage initializes again, creating a new instance. In effect, the app is loading from scratch after giving me a peek of what was previously open.
That is obviously undesired behavior. I want to use the existing instance to perform my task.
Attempt 1:
Use e.Cancel = true; to cancel the navigation to the MainPage.xaml:
(using the App.xaml.cs code from the official Fast App Resume sample to identify how the app was launched)
...
else if (e.NavigationMode == NavigationMode.New && wasRelaunched)
{
// This block will run if the previous navigation was a relaunch
wasRelaunched = false;
if (e.Uri.ToString().Contains("="))
{
// This block will run if the launch Uri contains "=" (ex: "id=XX") which
// was specified when the secondary tile was created in MainPage.xaml.cs
sessionType = SessionType.DeepLink;
e.Cancel = true; // <======================== Here
// The app was relaunched via a Deep Link.
// The page stack will be cleared.
}
}
...
Problem: In doing so, my OnNavigatedTo event handlers never fire, so my query string is never parsed.
protected override void OnNavigatedTo(System.Windows.Navigation.NavigationEventArgs e)
{
String navId;
if (e.NavigationMode != System.Windows.Navigation.NavigationMode.Back)
{
if (NavigationContext.QueryString.TryGetValue("id", out navId))
{
MessageBox.Show(navId.ToString()); // Not reached
}
}
...
Attempt 2:
Use e.Cancel = true; to cancel the navigation to the MainPage.xaml, AND pass the Uri to a method in MainPage:
// App.xaml.cs
...
else if (e.NavigationMode == NavigationMode.New && wasRelaunched)
{
// This block will run if the previous navigation was a relaunch
wasRelaunched = false;
if (e.Uri.ToString().Contains("="))
{
// This block will run if the launch Uri contains "=" (ex: "id=XX") which
// was specified when the secondary tile was created in MainPage.xaml.cs
sessionType = SessionType.DeepLink;
e.Cancel = true;
MainPage.GoToDeepLink(e.Uri); // <======================== Here
// The app was relaunched via a Deep Link.
// The page stack will be cleared.
}
}
...
// MainPage.xaml.cs
public static void GoToDeepLink(Uri uri) // <======================== Here
{
// Convert the uri into a list and navigate to it.
string path = uri.ToString();
string id = path.Substring(path.LastIndexOf('=') + 1);
MyList list = App.ViewModel.ListFromId(Convert.ToInt32(id));
pivotLists.SelectedItem = list;
}
Problem: I get an error that pivotLists is non-static and thus requires an object reference. I think that in order to get this to work I'd need to create a new instance of MainPage (MainPage newMainPage = new MainPage();) and call newMainPage.pivotLists.SelectedItem = list; -- BUT I don't know how to use newMainPage instead of the existing one/replace it... or if that's something I want/won't cause further problems/complications.
I don't know what the solution is to this problem, and I may be going in the completely wrong direction. Please keep all suggestions in simple terms with code examples if you can, I'm still learning.
Thanks for any help.

It seems that when you reopen your App from secondary tile, then it's reactivated and new instance of MainPage is created (even if there is one from previous run). If I understood you correctly, I've managed to do such a thing:
In app.xaml.cs:
I've added a variable which indicates if I should return to previous MainPage after Navigating from secondary tile - it needs to be static as I want to have access to it from MainPage
public static bool returnPage = false;
In RootFrame_Navigating I'm setting this variable to true in:
// ...
else if (e.NavigationMode == NavigationMode.New && wasRelaunched)
{
// This block will run if the previous navigation was a relaunch
wasRelaunched = false;
returnPage = true;
// ...
In ClearBackStackAfterReset - prevent from deleting the old Page, when returning:
// ...
if (e.NavigationMode != NavigationMode.New || returnPage)
return;
// ...
In MainPage.cs:
I've changed a little constructor, as I don't want to see a blink of a new Page:
public MainPage()
{
if (!App.returnPage)
InitializeComponent();
}
In MainPage I've also variable which is passed from secondary tile - it's also static, as I need only one instance of it:
private static string navId = "";
And the core of the trick - OnNavigatedTo:
protected override void OnNavigatedTo(NavigationEventArgs e)
{
if (App.returnPage)
{
App.returnPage = false;
NavigationContext.QueryString.TryGetValue("id", out navId);
NavigationService.GoBack();
}
else if (e.NavigationMode != NavigationMode.Reset)
{
// normal navigation
}
}
It works like this:
when you launch normally your App, returnPage is false, everything goes normal
when you activate it from secondary tile few things happen:
1. first goes navigation to your previous page with NavigationMode.Reset - we are not interested in it, so I switched it off - nothing should happen
2. then program tries to create new instance of MainPage, but returnPage is true, and because of the if statement, InitializeComponent won't run. Just after this, in OnNavigatedTo, program saves passed querystring and Navigates Back to previous instance of MainPage - from previous run
3. at last we are navigating to right MainPage with NavigationMode.Back and we have our querystring saved in static variable.
You must be aware of two things: first - probably it can be little rebuild (I'm not sure if wasRelaunched is needed and so on) - you need to debug it and see of what you can get rid off. Second - you will probably need to test your App with Tombstone case.
Hope this helps.

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!