I have an issue with navigation. When I click home screen button of device and get back to app I get app homescreen instead of pin page. Ideally it should show pin page and its working fine with back button of device.
OnStart() method has navigationasync but the same is not working with OnResume() method.
Do I have to go to each of the Platform project cs file and add the navigation there like for Android OnRestart()/OnResume() method?
If anyone knows the solution please let me know
Most commonly when writing your Xamarin Application with Prism you will have something like:
protected override void OnInitialized()
{
NavigationService.NavigateAsync("SomePage");
}
OnInitialized is called each time the App's ctor is invoked. This is an important consideration here because this means that any time that the native platform tombstones the app in the background or otherwise refreshes the app by calling OnCreate in your MainActivity or FinishedLaunching in your AppDelegate, then OnInitialized will be invoked resetting your App's Navigation stack to SomePage.
You can however override the OnStart/OnResume in PrismApplication and use whatever business logic you need to determine where to navigate and how you might want to restore your application.
public override void OnStart()
{
NavigationService.NavigateAsync("MainPage");
}
public override void OnResume()
{
if(someCondition)
{
NavigationService.NavigateAsync("SomePage");
}
else
{
NavigationService.NavigateAsync("AnotherPage");
}
}
Related
I am attempting to code an App in Xamarin Forms.
Upon startup, if the app is logged in the the user will be taken to the main shell with flyouts etc. If they are not logged in, then they will be taken to the signup/login page.
I have the following code in my App.xaml.cs
public App()
{
Instance = this;
InitializeComponent();
AssessStartupPage();
}
public void AssessStartupPage()
{
if (App.LoggedInUser == null)
{
SwitchToSignupPage_OTP();
return;
}
SwitchToShell();
}
public void SwitchToSignupPage_OTP() => SwitchMainView(new SignupPage_OTP());
public void SwitchToShell() => SwitchMainView(new AppShell());
When I attempt to switch to the shell from another Page (by calling App.Instance.SwitchToShell) the following exception is thrown:
Java.Lang.RuntimeException
Font asset not found sans-serif-medium
However if I change the AssessStartupPage() function which is called on startup to this:
public void AssessStartupPage()
{
SwitchToShell();
return;
}
The shell loads correctly at startup. However I need to be able to have the Signup page load at start if the user is not signed in and therefore need to be able to switch to the shell once signup is complete.
I have updated all the xamarin forms and xamarin essential libraries to the latest stable version but nothing seems to help.
The problem doesn't occur when I debug the app in UWP mode.
For the past 2 month I have been searching tirelessly for a way to implement a proper Page.Loaded event when using Xamarin.Forms but I couldn't implement or find a way to do it.
Most people suggest overriding Page.OnAppearing or adding an event handler for Page.Appearing both of which are not the answers or the proper way to achieve the desired effect and don't event behave as a real Page.Loaded event would.
I would like to know the following:
Why doesn't Xamarin.Forms have a built-in Page.Loaded event?
Is there's a work around?
Can I implement it from the native side?
Edit:
What I mean by "proper Page.Loaded" event is:
It must be called ONCE AND ONLY ONCE the page has loaded all of it's controls, laid them out, initialized them and rendered them for the first time.
It must NOT be called when returning from modal pages.
1.Why not load the data/controls in the constructor of the ContentPage? The constructor method is call only once and it is also called before Page.OnAppearing.
Can I implement it from the native side?
Yes, I think you can.
In iOS, override the ViewDidLoad method in custom renderer:
[assembly:ExportRenderer (typeof(ContentPage), typeof(MyPageRenderer))]
namespace App487.iOS
{
public class MyPageRenderer : PageRenderer
{
protected override void OnElementChanged(VisualElementChangedEventArgs e)
{
base.OnElementChanged(e);
}
public override void ViewDidLoad()
{
base.ViewDidLoad();
//call before ViewWillAppear and only called once
}
public override void ViewWillAppear(bool animated)
{
base.ViewWillAppear(animated);
}
}
}
In Android, try to override the OnAttachedToWindow method:
[assembly: ExportRenderer(typeof(ContentPage), typeof(MyPageRenderer))]
namespace App487.Droid
{
public class MyPageRenderer : PageRenderer
{
public MyPageRenderer(Context context) : base(context)
{
}
protected override void OnElementChanged(ElementChangedEventArgs<Page> e)
{
base.OnElementChanged(e);
}
protected override void OnAttachedToWindow()
{
base.OnAttachedToWindow();
}
}
}
Currently Xamarin.Forms doesn't not provide a proper/complete life cycle events to fulfill all specific requirements, but things are improving, the Dev team is currently working on to address this issue, below mentioned issues and recent pull request on the official GitHub Repos (you may follow, get ideas and maybe implement it yourself before they even ship it), they will for sure provide that in the future, although it is not clear when it will be ready.
Specification: Enhancement Add better life cycle events #2210.
Issue: LifeCycle events for controls #556.
Pull request: Life cycle events for controls
GitHub Branch where currently working on.
MAUI repo (Next evolution of Xamarin) Cross-Platform LifeCycle.
Specification Add Loaded/Unloaded to VisualElement.
I am creating app in Xamarin.Forms shared proeject. I want to detect app when it comes from background
currently, I have implemented OnActivated method in AppDelegate but this method is also called when we open control center in iphone. I want my app to reconnect with my server when app comes to foreground from background and show message accordingly but this message is also shown when I swipe up and open control center.
In native Xamarin.iOS app, there is a method WillEnterForegroundNotification but this method is not available here.
Is there any method that's called only if app comes from background ?
in App.xaml.cs
protected override void OnResume()
In native Xamarin.iOS app, there is a method
WillEnterForegroundNotification but this method is not available here.
You can access WillEnterForegroundNotification method in Xamarin.forms project, just override it in AppDelegate.cs:
public partial class AppDelegate : global::Xamarin.Forms.Platform.iOS.FormsApplicationDelegate
{
//
// This method is invoked when the application has loaded and is ready to run. In this
// method you should instantiate the window, load the UI into it and then make the window
// visible.
//
// You have 17 seconds to return from this method, or iOS will terminate your application.
//
public override bool FinishedLaunching(UIApplication app, NSDictionary options)
{
global::Xamarin.Forms.Forms.Init();
LoadApplication(new App());
return base.FinishedLaunching(app, options);
}
public override void WillEnterForeground(UIApplication uiApplication)
{
//handle your event here
base.WillEnterForeground(uiApplication);
}
}
Can someone point me to an example of how to leverage IApplicationLifecycleAware for Prism and Xamarin.Forms? I have a view model that implements it but OnResume and OnSleep never fire (although it fires within my App.xaml.cs).
To use IApplicationLifecycleAware you simply need to implement it on any ViewModel you wish to use it, and add the code to the OnSleep and OnResume methods that you require.
It is very important though that if you implement an override of these methods in your App class that you include the base execution otherwise the PrismApplication cannot execute the IApplicationLifecycleAware methods on the ViewModel of your current page.
public partial class App : PrismApplication
{
protected override void OnSleep()
{
// Handle IApplicationLifecycle
base.OnSleep();
// Handle when your app sleeps
}
protected override void OnResume()
{
// Handle IApplicationLifecycle
base.OnResume();
// Handle when your app resumes
}
}
I am sorry, if this question is asked before, but I am unable to find my answer that is why I am asking again this question.
My Scenario is I have placed a back button on my axml views from which I am performing Navigation of Going back on previous views using GoBack() Method.
what I need I want to disable back button on my hardware so that my app should not go back to previous screens which are available in the navigation stack. I am using Prism MVVM for my app, so is there any possibility to disable this button or have some overrideable action method on my ViewModel from which I should stop it.
Hope you could understand my question.
B.R
I found the best way to do this was to use the provided override of OnBackPressed in the android MainActivity and then access a bool I saved somewhere. I use the settings plugin personally but the example below uses the built in application properties (it should work but I haven't tested it).
public class MainActivity : FormsApplicationActivity
{
protected override void OnCreate(Bundle bundle)
{
base.OnCreate(bundle);
Forms.Init(this, bundle);
LoadApplication(new App());
}
public override void OnBackPressed()
{
var disable = (bool) App.Current.Properties["isBackButtonDisabled"];
if (disable) return;
base.OnBackPressed();
}
}