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I need some sample code on how to migrate from OnBackPressed, as I now need to target API 33. I've seen posts like:
https://medium.com/tech-takeaways/how-to-migrate-the-deprecated-onbackpressed-function-e66bb29fa2fd
which is java. For C#, I've seen this:
but couldn't get that to work. My OnBackPressed starts another activity, and "this" never worked right. I've also seen Kotlin samples, but nothing really for Xamarin.
I use Visual Studio 2022 and tried installing NuGet AndroidX packages, compatibility packages, and it was just a rathole. I even tried migrating the product to AndroidX, and that was a pain as well.
What is the best way to migrate this simple OnBackPressed code:
public override void OnBackPressed ()
{
var myActivity= new Intent (this, typeof(MyActivity));
StartActivity (myActivity);
}
I've tried the stuff in these posts but couldn't get it working. Any sample Xamarin code out there? Thanks a lot.
One more note: substituting OnKeyDown in place of OnBackPressed and looking for Keycode.Back gets rid of the warnings and seems to work, but this seems like regressing to Android 2.0. If I'm going to use API 33, it seems like I should take advantage of the new stuff.
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May I know whether your issue has been solved or not? If not, please share it in here. We can work together to figure it out.
I decided that this one was not worth the hassle, as OnKeyDown works fine, and I don't really need the Gesture stuff. I have other issues with other methods (like GetParcelableExtra and others) but I guess that has nothing to do with this thread. I'll probably ask that in another thread.
Thanks for your feedback.
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You should use the methods that the docs recommend that you use. If you cannot get them to work then please post example code of what is not working with the newer methods and tell us exactly what errors you're getting. We have no way of knowing why your code isn't working with the new stuff without seeing it fail.
The first post listed in my question was Kotlin. What is the C# equivalent of this code?:
**private val onBackPressedCallback: OnBackPressedCallback = object : OnBackPressedCallback(true)** {
override fun handleOnBackPressed() {
showAppClosingDialog()
}
}
In the second post I listed, they use private classes, etc. I think I got around that by nesting class, but then they say to add this code to the Main activity:
OnBackPressedDispatcher.AddCallback(new BackPress(this));
But when I put that line in my OnCreate method, I get CS0120 -- object reference required for non-static method OnBackPressedDispatcher.AddCallback. Adding a "this" parameter first, just says I can't convert between my activity and AndroidX.Lifecycle.ILifecycleOwner.
Also, I would rather not use a private class; I just wanted this as part of my activity, as the overridden OnBackPressed was.
So I was really just looking for a C# sample to handle the new way of doing OnBackPressed. There used to be a lot of them, but now it's pretty much Kotlin and Java.
Based upon this doc 13 isn't supported by Xamarin yet. The Github releases shows that it is though so there is a disconnect here. I don't code for Android and I cannot find any docs on the stuff you're talking about. But here's a Stack Overflow post where someone demonstrates doing what I think you're asking for in C#. Try to see if it solves your problem.
As for private classes, you likely don't need that (or nested). For encapsulation purposes perhaps but at runtime it doesn't care. Just create a regular class and optionally set its accessibility to internal and it would effectively be private.
Thanks. 13 seems to be supported by Xamarin in Visual Studio 2022. I had seen that post but glossed over it because I'm not using fragments. But you're right -- this post should help. It's probably the best I'm going to see.
I'll probably just go back to OnKeyDown. That post was written 11 years ago, and you still have to override OnBackPressed. I want to get rid of all the compiler warnings about OnBackPressed, especially because it may just stop working in the future. So I wanted to do it the new way, using the gesture stuff, but it seems like more trouble than it's worth. I hate to go all the way back to OnKeyDown, but that will probably always work, since for some reason, they don't seem to have deprectated it.
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@Michael Taylor
Xamarin.Android has been supporting Android 13 for months now.
If you are going to target Android 13 it is not optional to use androidx packages - you have to. The androidx packages were introduced in Android 10, so they aren't exactly new, so you will have to jump into your rat hole. The migration idea was meant to be an assistance package in helping you migrate, but when I tried it years ago, it really wasn't all that useful. It is far easier just to replace all the old Support packages with their equivalent AndroidX packages. In fact, I don't think the migration package is even supported anymore.
I have a number of tutorials using Android's NavigationComponent (Google's recommendation for modern Android development - Single Activity/Multiple Fragments) that would help/guide you in converting an existing old project.
An OnBackPressedCallback class (C# version of the Kotlin code above) is introduced in the second project NavigationGraph2 to handle back key and back gestures and is used in all the following projects. You'll see in each fragment of each of the projects how the OnBackPressedCallback class is instantiated.
The medium article above regarding predictive back gesture is a step further (only available via Settings developer options) that is at the moment not even available to Xamarin developers until Xamarin.Android.AppCompat 1.6.0 is released - the latest version is 1.5.1, so there is no immediate need to concern yourself with that feature.
The .dot Maui Android example, var Navigation I think uses the NavigationComponent internally, however, I don't understand the use of the following code
activity.FinishAndRemoveTask();
Process.KillProcess(Process.MyPid());
as that would kill the application and so prevent a warm start. You would typically use the above code if you were testing the SplashScreen API to ensure that each time you started the app, it would always do a cold start so that you could confirm that the application icon displays correctly.
Your idea of starting an Activity via a back key press or back gesture just doesn't fit with modern Android development, so you will need to come up with a more appropriate method such as a menu item etc. Back key and back gestures are for navigating backwards - not forwards.
You can find these tutorials at https://github.com/gmck. Each project has the same docx file, so you can read ahead before you tackle each project.
This answer expands on my previous answer.
This test app demonstrates how to replace the now deprecated Activity.OnBackPressed with an OnBackPressedCallback in conjunction with using the new Predictive Back Gesture for Android 13
It, first determines if the user is using Gesture navigation.