I see a lot of threads on this sort of subject but none seem to apply to my question. I don't have a navigation page, I have a hamburger menu -- so Push/PopAsync() would not appear to be the answer. And I don't want to go to a specific page, I want to go back to the previous page (whatever it was) so GoToAsync() would not appear to be the answer.
Xamarin app for Android and UWP with iOS somewhere in the future. The description of the problem below is specific to Android; it works a little differently on UWP.
I want to put a Help entry in the hamburger menu that will take the user to a help page in the default browser. Hamburger menu seems to only go to an app page, so I defined a "dummy" View page that displays "Loading ..." and issues Browser.OpenAsync() in its OnAppearing() method, and that pretty much works. The problem is that the user would expect that the Back button would take him or her to the page they were on before clicking Help. I tried a couple of things. I have gotten close with the following but it does not quite work correctly:
In each of my other Views' OnAppearing() I call a method that saves the value of Current.MainPage.CurrentItem in a static. Then in the Help page after the OpenAsync() I set Current.MainPage.CurrentItem to its setting from the last page before the Help page.
Console.WriteLine("#### HelpPage loading Web Help");
_ = State.DisplayHelpPage(this, "MainHelp"); // _ = await Browser.OpenAsync(uri, blo);
Console.WriteLine("#### HelpPage returning to previous page");
State.ReloadPreviousPage(); // Current.MainPage).CurrentItem = lastFlyoutItem;
It almost works. The first time I click Help in the hamburger menu I get
#### HelpPage loading Web Help
#### HelpPage returning to previous page
#### HelpPage loading Web Help
#### HelpPage returning to previous page
The Web page loads perfectly. But when I click the Back button it displays again. Obviously my OnAppearing() method has been driven twice, which I do not understand.
If I click the Back button again I come back to the previous page in the application just as I wanted. The next time I click Help in the Hamburger menu it takes me to my dummy View page with no Web page. Obviously, my OnAppearing() is not being driven at all. But after that it works perfectly. I can go to any app page, and click Help in the menu. I get the Web page, and the Back button takes me back to the app and the page. In UWP of course the browser does not load on top of the app Views, and I seem to see it being loaded twice every time.
So ... what should I be doing differently? And why is my OnAppearing() being driven twice and then not at all ... and thereafter as I would expect?
There are several parts to this answer:
Get the previous page on to the Navigation stack. This is done by intercepting the Route "//HelpPage", and replacing it with a route that ISN'T a child of Shell.
Remember "FakePageVisible", so we know to do "PopAsync" in OnResume, when app returns from browser.
(Optional) "Entering" flag prevents going to browser twice.
App.xaml.cs:
public partial class App : Application
{
public App()
{
InitializeComponent();
MainPage = new AppShell();
}
protected override void OnResume()
{
if (HelpPage.FakePageVisible) {
HelpPage.FakePageVisible = false;
var shell = MainPage as AppShell;
if (shell != null) {
shell.Navigation.PopAsync();
}
}
}
}
AppShell.xaml.cs:
public partial class AppShell : Xamarin.Forms.Shell
{
public AppShell()
{
InitializeComponent();
// Define a route that isn't a child of Shell.
Routing.RegisterRoute("Help2", typeof(HelpPage));
}
protected override void OnNavigating(ShellNavigatingEventArgs args)
{
base.OnNavigating(args);
if (args.Current != null) {
if (args.Source == ShellNavigationSource.ShellItemChanged) {
if (args.Target.Location.OriginalString == "//HelpPage") {
// Cancel the original route.
args.Cancel();
Device.BeginInvokeOnMainThread(() => {
// Used by the next OnAppearing.
HelpPage.Entering = true;
// Go there by a route that isn't a child of Shell.
// Doing so, pushes our previous location on to Navigation stack.
Shell.Current.GoToAsync("Help2");
});
}
}
}
}
}
HelpPage.xaml.cs:
public partial class HelpPage : ContentPage
{
public static bool Entering;
public static bool FakePageVisible;
protected override void OnAppearing
{
// Make sure this only happens once (just in case).
if (Entering) {
Entering = false;
FakePageVisible = true;
Xamarin.Essentials.Browser.OpenAsync("https://aka.ms/xamarin-quickstart");
}
}
}
For a simple demo, this code communicates via static variables in HelpPage. Re-factor as appropriate for your situation.
Related
I am building an app that makes use of some App links. In below example, I want to open a ResetPasswordPage when the user activates a link from an e-mail.
protected override async void OnInitialized()
{
InitializeComponent();
await NavigationService.NavigateAsync("/NavigationPage/LoginPage");
}
protected override void OnAppLinkRequestReceived(Uri uri)
{
if (uri.Host.EndsWith("site.nl", StringComparison.OrdinalIgnoreCase))
{
if (uri.AbsolutePath.StartsWith(#"/appname/resetpassword/"))
{
if (uri.Segments.Length == 4)
{
string resetCode = uri.Segments[3];
NavigationParameters param = new();
param.Add(NavConst.PasswordResetCode, resetCode);
await NavigationService.NavigateAsync("ResetPasswordPage", param);
}
}
}
}
This code works, but not what I would expect (for both iOS and Android). I would expect that ResetPasswordPage would be added to the navigation stack that was set in OnInitialized, so that it would contain a back button in the navigation bar, bringing the user back to the login page in this case.
But instead, it looks like the navigation stack gets replaced. When ResetPasswordPage is shown, and the user clicks the hardware back button, the app is closed. However, i want it to go back to where the user was before.
Am I not understanding some navigation concepts well or might this be a bug?
The NavigationService is a rather unique service within Prism for Xamarin.Forms. It is constructed new for each page as navigation and the navigation stack is dependent on where you are navigating from.
For instance when you Navigate from the context of a MasterDetailPage / FlyoutPage, it understands that you aren't trying to push a modal on top of that page but instead you are starting from the context of Detail/Flyout. If the NavigationService continually updated the Page context then the navigation service injected into that MasterDetailPage/FlyoutPage's ViewModel would have no idea that it needed that page as the context to navigate from.
Your issue here ultimately is that you are Navigating from the context of the Application which has a NavigationService with no Page set. As a result even a relative Navigation will still have the effect of an absolute Navigation thus resetting the Application.MainPage since that NavigationService does not have the contextual understanding of another page.
Depending on your business requirements you have a few different options. One is to do an absolute Navigation that gives you navigation stack that you're looking for.
Optionally you may want to get the currently displayed page and update the NavigationService to understand it. In the App class you might add something like:
protected override void OnAppLinkRequestReceived(Uri uri)
{
if (NavigationService is IPageAware pa)
{
page.Page = PageUtilities.GetCurrentPage(MainPage);
}
if (someCondition)
{
// This will now navigate from relatively from the page
// returned by GetCurrentPage.
NavigationService.NavigateAsync("SomeRelativeUrl")
.OnNavigationError(HandleNavigationError);
}
}
Relatively new to Xamarin, hitting an issue with PushAsync and navigation I can't figure out.
I have a main navigation page, and then a "MyContentPage" that is responsible for rendering a dynamic list based on a supplied id. When the user clicks on a list item they go to a next (newed up) "MyContentPage" (same class) with a different id. Basically a recursive page hierarchy based on a local db.
Problem is that navigation seems to quickly get messed up in some way I can't work out. The pages get swapped around, or get lost. Navigating back to root, if I click back down again, it skips to a page that is further down etc.
So basically the one page apart from the main page (which has multiple navigationpages in tabs - though I only use one tab at this point) binds its controls to this function:
public async Task NavigateToContent(int contentId)
{
await ((Application.Current.MainPage) as TabbedPage)?.CurrentPage.Navigation.PushAsync(new MyContentPage(contentId));
}
The above is then used recursively. Ie. Similar controls bind to the same function until there are no further pages to click down to.
The MyContentPage constructor loads the model:
public MyContentPage(int id)
{
InitializeComponent();
_id = id;
BindingContext = viewModel = new ContentPageViewModel(id);
}
What is the issue here?
From what you mentioned in comments, the issue is caused by the navigation code called in the 'service' class. When you call the service method multiple times, it actually changes the current navigation stack in xamarin forms. Move the page navigation code from service class to viewmodel class.
Or try to put the page navigation source code into something like 'NavigationService' (one example is the one in https://learn.microsoft.com/en-us/xamarin/xamarin-forms/enterprise-application-patterns/ ) and inject this service into your view model class.
OK so this all turned out to be an issue with concurrency.
The original button click was like this:
private void Button_Clicked(object sender, EventArgs e)
{
Task.Run(async () => await (BindingContext as ContentPageViewModel).ExecuteNavCommand(sender));
}
But this resulted in a UI operation happening on a different task
The event handler can be declared as async
The correction is
private async void Button_Clicked(object sender, EventArgs e)
{
await viewModel.ExecuteNavCommand(sender);
}
I have manually/programmatically set up an up button in my toolbar for a fragment page with the following code in onCreateOptionsMenu in the fragment:
(activity as AppCompatActivity).setSupportActionBar?.setDisplayHomeAsUpEnabled(true)
Tapping the system back button will take the user back to the previous fragment but without an up button (that works) I think some users may get lost.
I am having difficulty trying to work out how to catch and handle the up button to pop the fragment off the back stack.
This SO post shows how to catch the the up button click however it is in Java and doesn't go on to explain how you would navigate up.
I think it needs to look something like the code below but there are errors everywhere:
The case android.R.id.home is showing an 'Incompatible types:Int and MenuItem' error?
onBackPressed() is showing an 'Unresolved reference' error.
Bad code:
override fun onOptionsItemSelected(item: MenuItem?): Boolean {
when (item) {
android.R.id.home -> {
onBackPressed()
return true
}
else -> return super.onOptionsItemSelected(item)
}
}
UPDATE:
A comment to another SO post has a potential solution in Kotlin. It catches the click on the up button and goes back to the previous fragment page but then the up button doesn't go away. So the up button now persists even on the top level fragment destinations in my app (the pages corresponding to each tab in the BottomNavigationView).
I think this might have to do with the fact that there is only one activity in my app and the way that I have set up the up button in the fragment as mentioned above? If so, is there a workaround or other way to set up the up button by referencing the fragment instead of the whole activity?
If it helps, this is the code in the RecyclerView inner ViewHolder class in the adapter.kt file that navigates to the fragment page in question:
class AdapterListItemDetails(val items: List<ItemsList>) : RecyclerView.Adapter<AdapterListItemDeatils.ItemsViewHolder>() {
//overrides for OnCreateViewHolder, getItemCount, onBindViewHolder
inner class ItemsViewHolder(itemView: View) : RecyclerView.ViewHolder(itemView) {
var currentItem: ItemsList? = null
var currentPosition: Int = 0
init {
itemView.setOnClickListener(Navigation.createNavigateOnClickListener(R.id.goto_details, null))
}
fun setData(itemsList: ItemsList, position: Int) {
itemView.tview_Keys.text = itemsList!!.nameText
this.currentItem = itemsList
this.currentPosition = position
}
}
}
You have to override onBackPressed() method in activity and handle the fragment transactions with your manual code. If you could share some snippet of activity and fragment transactions will help me to give some proper solution.
Hi this is what i usually do:
in an activity find the navController from your navHostFragment
val navController = this.findNavController(R.id.myNavHostFragment)
Make sure it's connected to the ActionBar
NavigationUI.setupActionBarWithNavController(this, navController)
Then simply override onSupportNavigateUp, find your navController then navigate up
override fun onSupportNavigateUp(): Boolean{
val navController = this.findNavController(R.id.myNavHostFragment)
return navController.navigateUp()
}
I have two pages: Page A and Page B. I want that the user on my application be able to pass since page A to page B, but I don,t want he to be able to pass since page B to page A. How can I do that?
I tryed to use Navigation Page and deactivate the return Button, but I couldn't find how deactivate it.
If you don't need to "Navigate" you can set
Application.Current.MainPage = new PageB();
and override OnBackButtonPressed()
protected override void OnDisappearing()
{
//back button logic here
return true;
}
I am trying to implement a login scenario with Xamarin Forms and Prism.
My application root page is a MasterDetail page (HomeMasterDetailPage); this being used to provide the side menu.
What I am trying to do is to have the HomeMasterDetailPage page shown with Content set to an instance of LoginPage. When the user logs in, the Content should change to an instance of HomeDetailContentPage. It should not be possible to return to the LoginPage using the back button.
I am using the NavigationService from Prism Forms.
My start up is like this...
public partial class App : PrismApplication {
public App(IPlatformInitializer initializer = null)
: base(initializer) {
}
protected override void OnInitialized() {
InitializeComponent();
Uri uri = new Uri($"/{nameof(NavigationPage)}/{nameof(HomeMasterDetailPage)}/{nameof(HomeDetailContentPage)}", UriKind.Absolute);
var settings = Container.Resolve<SettingsService>();
if (!settings.DeviceUserID.HasValue)
uri = new Uri($"/{nameof(NavigationPage)}/{nameof(HomeMasterDetailPage)}/{nameof(LoginPage)}", UriKind.Absolute);
NavigationService.NavigateAsync(uri);
}
protected override void RegisterTypes() {
Container.RegisterTypeForNavigation<NavigationPage>();
Container.RegisterTypeForNavigation<LoginPage, LoginPageViewModel>();
Container.RegisterTypeForNavigation<HomeMasterDetailPage, HomePageViewModel>();
Container.RegisterTypeForNavigation<HomeMasterContentPage>();
Container.RegisterTypeForNavigation<HomeDetailContentPage>();
}
}
This correctly displays the LoginPage within the HomeMasterDetailPage if the user is not already logged on, and the HomeDetailContentPage within the same HomeMasterDetailPage if the user is logged on.
The problem comes when actually logging on; the following is the code within the view model for the LoginPage...
protected async Task ExecuteLoginCommand() {
Uri uri = new Uri($"/{nameof(NavigationPage)}/{nameof(HomeMasterDetailPage)}/{nameof(HomeDetailContentPage)}", UriKind.Absolute);
await this.navigationService.NavigateAsync(uri);
}
It is my understanding that by using an absolute Uri this should reset the navigation so that the new page arrangement (/NavigationPage/HomeMasterDetailPage/HomeDetailContentPage) is at the top and bottom of the stack, allowing me to then move forward from there. Instead, I am getting an unhandled exception (on Android 7.0).
What am I doing wrong?
Note: All of the examples that I see have the MasterDetailPage at the root with Content being set to NavigationPage/ContentPage; when I try this I do not get exceptions, however the side menu operates differently within the MasterDetailPage - when you tap on the "hamburger" the side menu slides in over everything (including the action/title bar) and the only way to clear it is to tap outside of the side menu that slides in whereas when I show the MasterDetailPage within a NavigationPage the side menu slides in below the action/title bar and the hamburger changes to an arrow that you can click to hide the side menu again.
I can't say I've tested this exact scenario. However, if your LoginPage is the Detail of a MasterDetailPage, you may not want to perform the navigation from the LoginPage. You could, instead create a SuccessfulLoginEvent, which you would then publish from the LoginPage using the IEventAggregator, and you would subscribe to on your MasterDetailPage's ViewModel. You could then perform the navigation as _navigationService.NavigateAsync("NavigationPage/ViewA") and it should reset the Detail such that the back button doesn't bring you to the LoginPage.
Alternatively, you can simply perform an absolute Navigation which has the effect of:
Application.Current.MainPage = new MyPage().
To do to this, you could do the navigation from anywhere as:
_navigationService.NavigateAsync("/MyMasterDetailPage/NavigationPage/ViewA")