I'm using a leanback BrowseFragment to implement a simple android tv app. I have two PageRows which are backed by custom fragments. When I switch between the two in the browse navigation area, the content side of the screen goes blank briefly before the new fragment's views appear. How can I fade from one view to the other without a delay in between?
I see some references to "entrance transition" in the docs which I think is what I need, but I can't find any examples of what to do in those callbacks.
https://developer.android.com/reference/android/support/v17/leanback/app/BrowseFragment.MainFragmentAdapter.html#setEntranceTransitionState(boolean)
I tried to implement setEntranceTransitionState on my PageRow Fragment's MainFragmentAdapter, but it is never invoked:
class GuideFragment: Fragment(), BrowseFragment.MainFragmentAdapterProvider {
val fragmentAdapter = object: BrowseFragment.MainFragmentAdapter<GuideFragment>(this) {
override fun setEntranceTransitionState(state: Boolean) {
Log.v("TEST", "setEntrance($state)")
fragment.setEntranceTransitionState(state)
}
}
override fun getMainFragmentAdapter() = fragmentAdapter
}
There is no way to do this when using BrowseSupportFragment.
If you look at the implementation of swapToMainFragment(), you'll see that while scrolling the content is set to an empty fragment. When SCROLL_STATE_IDLE is reached, a regular fragment transaction is used to replace the child fragment with the new content.
leanback has a lot of limitations, It is better to fork the official code and create your own repo and modify it; we did the same in our app.
Related
I have an app with four main pages, switched through a tab bar (no "back" button).
One page has a lot of content (ScrollView) and takes quite a few seconds until it's rendered. I handle that by showing a "loading" overlay while the work is done. But for that specific page I'd like to keep the view alive, so that when the user switches to another page and comes back later, the page is ready without loading everything again.
I'm not sure how to do that in MvvmCross, though.
I did read the documentation and from what I understood the View Presenter would be the right way to do it, since the docs say:
"Another kind of presentation changes your app can request through
hints includes clearing / modifying the BackStack, changing a root
while maintaining the existent views, … possibilities are really
endless. Once again your app is king here!"
I guess I would need to create a custom MvxPresentationHint for that, but I don't quite get it :(
How or rather where would I access and store/load the View?
I'm generally still quite unfamiliar with MvvmCross (how it works under the hood) and especially customization of Mvx classes, even though I've been using it for a while.
Any explanation and preferably code examples beyond what's written in the documentation would be extremely appreciated!
It isn't meaningful to attempt to "store" a view in MVVM. The XF view is a representation of what will be created with native (e.g. "Android" or "iOS") widgets. Creating and measuring/laying out those native widgets is what is slow. MVVM View Presenter won't speed up that logic.
Instead of "store", you need "keep alive":
For a ContentPage called MyPage, when you create it, store it in a static variable. Then re-use that variable. If you never need more than one of these, you can store it in the class itself.
Modify the "code behind", MyPage.xaml.cs:
public partial class MyPage : ContentPage
{
// Singleton Pattern.
private static MyPage _it;
public static MyPage It {
get {
if (_it == null)
_it = new MyPage();
return _it;
}
}
// "private", because calling this directly defeats the purpose. Instead, use `MyPage.It`.
private MyPage()
{
InitializeComponent();
}
}
To create it, whereever you would put:
new MyPage()
instead put this:
MyPage.It
For instance, you might do PushAsync(MyPage.It);
This will always return the SAME INSTANCE of MyPage. So once it has been created, it keeps its state.
IMPORTANT: Note that the constructor is only called ONCE. Any code that needs to be done each time the page appears, put in override .. OnAppearing() method.
LIMITATION: Views "expect" to be part of the visual hierarchy when they are manipulated. If you attempt to alter the page or its view model while it is not on the screen, you may encounter problems. Those are beyond the scope of this answer - create a new StackOverflow question with the details of any problem you encounter.
I am developing a Xamarin.Forms app with Prism in which I'd like to incorporate an onboarding page (more specific a top user benefits page, following the Material Design guidelines).
The app itself is structured around a NavigationPage to which I navigate with
NavigationService.NavigateAsync("/NavigationRootPage/MainPage")
in my App(). On the first start I'd like to show the onboarding page instead and I am having quite some issues getting it right.
My first approach was to navigate to MainPage with
_navigationService.NavigateAsync("/NavigationRootPage/MainPage")
from my viewmodel, when the user clicks the Get Started! button. This kind of worked by is also kind of ugly, since this absolute navigation will destroy the oboarding page immediately and not animate the transition. Furthermore at the moment the oboarding page is destroyed, the MainPage will be built, which will take a small, but noticeable, amount of time. In effect the user will notice the MainPage being built up, which does not look smooth at all.
My second approach was to navigate in a relative fashion from my viewmodel.
_navigationService.NavigateAsync("NavigationRootPage/MainPage")
This works way smoother, with the transition animation and after the animation is done, the MainPage is already ready to go. But again there is a major drawback. You can navigate back to the onbaording page, which we dont't want neither. And - to my knowledge - there is no (clean) way to remove the page from the navigation stack, too. I tried calling PageUtility.DestroyPage on my onboarding page, but this only worsened things, since it seemed to keep the page, but destroy the viewmodel, resulting in my onboarding page being shown without data when pushing the back button.
My third approach did not work at all, although it seemed promising to me. In my App() I pushed my navigation page with the main page then then my onboarding page modal
NavigationService.NavigateAsync("/NavigationRootPage/MainPage");
NavigationService.NavigateAsync("OnboardingPage", useModalNavigation: true);
and then in my viewmodel
_navigationService.GoBackAsync(useModalNavigation: true)
but this approach
showed the header of the NavigationPage although the onbaording page was supposed to be shown as a modal
refused to GoBackAsync - when calling this method, nothing happens
waiting for the first call to NavigateAsync did not change anything either.
Some other things I've tried
Implemented INavigationOptions in my viewmodel with ClearNavigationStackOnNavigation being true
Tried setting Application.MainPage after my NavigationPage was shown, but to no avail
I would have believed that this was king of a common requirement when programming an app. Is there something I've missed? Or will I have to live with one of those drawbacks?
I think you are overthinking this. If you want to show your Onborading page first then just navigate to it first.
`NavigateAsync("NavigationPage/OnboardingPage");
Or if you want to have the MainPage in the stack, then start the app with a deeplink
`NavigateAsync("NavigationPage/MainPage/OnboardingPage");
If you don't want to show the navigation header, just hide it for the onboarding page.
Don't use an absolute navigation unless you want to completely reset the navigation stack (equivalent to MainPage = new MainPage()).
I have found a solution, which is not the most beautiful one (it is actually quite ugly) but working.
In my MainPages viewmodel I implemented INavigatingAware and navigated to my OnboardingPage modally
public async void OnNavigatingTo(NavigationParameters parameters)
{
await _navigationService.NavigateAsync("LandingPage", useModalNavigation: true);
}
However, removing the moal page with
this._navigationService.GoBackAsync(useModalNavigation: true);
does not work as expected. The modal is not removed (although it should work this way from looking at the code, but I did not manage to debug with Re# generated PDBs). Hence I had to go the ugly (non-MVVM) way and create an event handler for Button.Click and remove the modal manually
private void Button_OnClicked(object sender, EventArgs e)
{
this.Navigation.PopModalAsync();
}
This will return to my MainPage smoothly with an animation and my MainPageis already up and running without being built up while already visible.
Still, I'd appreciate an answer on how to do it the Prism way.
In PrismForms we got the problem, that the NavigationStack is empty after navigating to a new page. That means after using the hardware back-button on the SecondPage, the app is closed. Although the back-arrow in the header on Android isnt shown. If looking closely you can see the back-arrow for a short moment after the page is switched. I guess thats before the NavigationStack gets cleared.
To the first page we navigate with the following command in OnInitialized() in our App.xaml.cs which derives from PrismApplication.
NavigationService.NavigateAsync("NavigationPage/StartPage");
(If only Navigating to „StartPage“ here, the Stack doesnt get cleared.)
That has do to with PageNavigationService.ProcessNavigationForNavigationPage(...) calling
bool clearNavStack = GetClearNavigationPageNavigationStack(currentPage); and PageNavigationService.ProcessNavigationForContentPage(...) not.
From the StartPage to the next we navigate with NavigateAsync("SecondPage")“. Here the described behaviour appears.
For navigation we use a class which wraps the Prism NavigationService. We hold him as a property and get him via Unity in our constructor:
this.PrismNavigation = prismNavigation ?? throw new ArgumentNullException(nameof(prismNavigation));
The methods „NavigateAsync“ and „GoBackAsync“, etc. we just pass through.
This way we want to seperate our ViewModel-Project from references to XamarinForms to later be able to use the same ViewModels for for example a WPF-GUI.
Why is the stack beeing cleared by our own NavigationService? If we register the original Prism NavigationService in App.xaml.cs instead, navigating back works as expected again. We found the point in the framework and could avoid the clearing with a drity hack, but that’s against the navigation-logic implemented in PrismForms, but we don’t understand how to do it the correct way.
Every help appreciated!
We edited a few things to get it working after finding some interesting information by Brian Lagunas in the forlast-post here:
https://github.com/PrismLibrary/Prism/issues/591
Although the topic was about something else, it led to improvements for overwriting the Navigation Service.
Remember that in your viewModels the Navigation Service must be named "navigationService" by convention. Also we switched from just holding the Prism Navigation Service as a parameter to deriving from it as suggested in the link above.
public class MyNavigationService : UnityPageNavigationService
I have been reading about fragments lately, and almost everyone says that we should use it. I still can't understand the concept very well. I have read this, but I still have some questions.
First: A fragment must be related ( if its the right word) to an activity, let say MainActivity, the fragment has its own layout, the MainActivity has its own two. So what will be displayed on the screen? the fragment layout or the MainActivity or Both??
Second: If I want to convert an existing code to use fragments, what are the main changes?
Third: If I want to have more than one fragment, do I have to add a class that extends Fragment for each fragment I want to create??
Forth: onCreateView of the class that extends Fragment returns a view, is it correct to create a view inside it and return it for the main activity to add it to its layout??
Any help is appreciated.
Here are some tips about fragments what i understand so far , it might help you to understand Fragments :
1: About your first Question, yes both(Activity and Fragment) has their own layouts but Activity layout is act as base layout for fragments but this also depends on the layout you are working. If i state a simple example of HelloWorld app(which automatically created when you first create your Project in eclipse in updated adt), then you saw there Activity act as base and fragment layout show over it.
2: If you want to change the existing code to use fragments,firstly it depends upon the complexity of your code, and after that you have to change various things like if you are supporting api level 10 and below than you have to use Extra Libraries.there are lots of changes to be made but these all depends on your requirements.
3: Yes you have to create a Class which extends Fragment or any other Sub Class of Fragment. This Class is just like your Activity Class in which you have a xml layout to work with.
4: Yes you have to define a view inside OnCreateView() to return it to the activity to add to its layout or to show the UI.
Fragments are just like Activities , the pain comes when you working with Nested Fragments. and the life cycle of fragments are little different than Activity .
Note :please tell me if you have other queries or in case of any doubt about above written statements.
First:
In the layout of MainActivity you can embed multiple fragments layouts. You can even reuse these fragment layouts in any other activity. Ah, Good feature!
Second:
If I want to convert an existing code to use fragments, what are the
main changes?
To use fragments in your existing code you just need to,
The fragments will be added to the activity using the <fragment> element in the layout or can be added dynamically.
To check if the fragment is already part of your layout you can use the FragmentManager class -
DetailFragment fragment = (DetailFragment) getFragmentManager().
findFragmentById(R.id.detail_frag);
if (fragment==null || ! fragment.isInLayout()) {
// start new Activity
}
else {
fragment.update(...);
}
If a fragment is defined in an XML layout file, the android:name attribute points to the corresponding class.
To dynamically add fragments to an existing layout you typically define a container in the XML layout file in which you add a Fragment.
For this you can use, for example, a FrameLayout element.
FragmentTransaction ft = getFragmentManager().beginTransaction();
ft.replace(R.id.your_placehodler, new YourFragment());
ft.commit();
A new Fragment will replace an existing Fragment that was previously added to the container.
If you want to add the transaction to the backstack of Android, you use the addToBackStack() method.
This will add the action to the history stack of the activity, i.e., this will allow to revert the Fragment changes via the back button.
Third:
If I want to have more than one fragment, do I have to add a class
that extends Fragment for each fragment I want to create??
To define a new fragment you either extend the android.app.Fragment class or one of its subclasses,
for example, ListFragment, DialogFragment, PreferenceFragment or WebViewFragment.
Forth:
onCreateView of the class that extends Fragment returns a view, is it
correct to create a view inside it and return it for the main activity
to add it to its layout??
No need to return it to the main activity to add it to its layout. Just use FragmentTransaction's replace inside Main Activity followed by commit to be done.
I have a TitleWindow mxml class wich has several components, and listeners.
On its creationComplete and init state i add some listeners which listen for events on its gui.
This TitleWindow is only shown when the user click on a "button", i made TitleWindow a singleton with the following code:
public static function getInstance():MyWindow
{
if ( MyWindow.singleton )
{
return MyWindow.singleton;
}
else{
MyWindow.singleton = new MyWindow();
return MyWindow.singleton;
}
}
I needed a singleton because the user will call this window several times as much as he wants and i only need one.
The problem is the following on some special external events i need to "modify" some listeners (remove listeners and add new ones) on a button from MyWindow, before it was even shown once.
I still have MyWindow.getInstance() in memory when my application starts up.
However adding /removing listeners does not seem to have any effect if he actual rendering of the components did not happen, event when using the following code on app startup.
myWindow= MyWindow.getInstance();
myWindow.initialize();
Not suprisingly if i "show" ('render') the myWindow at least once then the events modifications on the myWindow instance works perfectly.
How can i fake the complete initialisation of this component without showing it on startup ?
Thanks !
Which sort of a container holds your button? If you are using a Multiple View Container you can try setting the creationPolicy to all. Single View Containers create all their children in one go and you shouldn't face this problem.
From Flex 3.0 docs I could retrieve this:
The default creation policy for all containers, except the Application container, is the policy of the parent container. The default policy for the Application container is auto.
This looks like the cause for all your troubles.
Update: I did not mention this earlier, since I thought this was to be expected :) Setting the creationPolicy to all makes your application load more slowly. So, read up on Ordered Creation -- this technique helps you to choose if the controls are displayed all in one go (which is the default behavior, after all of the controls have been created) or step-by-step, as and when they are created.