feat(core): back button event on Android, closes #8142

[lucasfernog]

I've used https://github.com/ionic-team/capacitor-plugins/blob/main/app/android/src/main/java/com/capacitorjs/plugins/app/AppPlugin.java as a reference here, checking if there's a back button event handler with a default of webview's goBack implementation

[github-actions]

Package Changes Through e52cfee

There are 11 changes which include @tauri-apps/api with minor, tauri-cli with minor, tauri-utils with minor, tauri-runtime-wry with minor, tauri-runtime with minor, tauri with minor, tauri-bundler with minor, @tauri-apps/cli with minor, tauri-build with minor, tauri-codegen with patch, tauri-macros with patch

Planned Package Versions

The following package releases are the planned based on the context of changes in this pull request.

package	current	next
@tauri-apps/api	2.8.0	2.9.0
tauri-utils	2.7.0	2.8.0
tauri-bundler	2.6.1	2.7.0
tauri-runtime	2.8.0	2.9.0
tauri-runtime-wry	2.8.1	2.9.0
tauri-codegen	2.4.0	2.4.1
tauri-macros	2.4.0	2.4.1
tauri-plugin	2.4.0	2.4.1
tauri-build	2.4.1	2.5.0
tauri	2.8.5	2.9.0
@tauri-apps/cli	2.8.4	2.9.0
tauri-cli	2.8.4	2.9.0

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[lucasfernog]

the exit impl still needs to be tested

[lucasfernog]

I've removed the App::exit impl - after further testing, the existing API is working fine

[FabianLars]

If i register a callback it seems to work fine but if i don't register one, i get [TAURI] Couldn't find callback id ... errors when i use the back button.
Also it likely was because of my scuffed testing but i couldn't really make use of canGoBack: true since it just navigates in that case. Any tips how to test this?

p.s. i had to merge #14132 into my local clone of this branch for the listener to work.

[lucasfernog]

If i register a callback it seems to work fine but if i don't register one, i get [TAURI] Couldn't find callback id ... errors when i use the back button. Also it likely was because of my scuffed testing but i couldn't really make use of canGoBack: true since it just navigates in that case. Any tips how to test this?

p.s. i had to merge #14132 into my local clone of this branch for the listener to work.

ohh i didn't realize wry handled this.. i'll push an update

[FabianLars]

One really weird thing (that i've seen elsewhere as well, just not this reliably) is that i have to manually shutdown the emulator if i want to re-run tauri android dev after registering a listener.

Otherwise this seems to work good now though i wonder if someone will ask for a way to remove the listener to restore native behavior at runtime. I assume that'll be rare so i think we can wait until that's actually needed?

[lucasfernog]

Otherwise this seems to work good now though i wonder if someone will ask for a way to remove the listener to restore native behavior at runtime. I assume that'll be rare so i think we can wait until that's actually needed?

onBackButtonPress returns PluginListener which is a class that has a unregister function (I also forgot about this, had to check lol)
it's similar to how listen() works but uses a class instead of a closure :|

[lucasfernog]

One really weird thing (that i've seen elsewhere as well, just not this reliably) is that i have to manually shutdown the emulator if i want to re-run tauri android dev after registering a listener.

I think it's unrelated. I've seen this when i use Android Studio and i click run or debug way too many times - it even breaks Android Studio itself after a while. I think it's related to the adb port forwarding, it gets stuck eventually.

[lucasfernog]

One really weird thing (that i've seen elsewhere as well, just not this reliably) is that i have to manually shutdown the emulator if i want to re-run tauri android dev after registering a listener.

@FabianLars you're right this indeed makes it a lot easy to reproduce this.. but only if you no-op on the back button handler.. if I do this it doesn't seem like it breaks:
await __TAURI__.app.onBackButtonPress(() => __TAURI__.process.exit())
maybe the emulator gets in a weird state? i'm not sure..

I've opened a couple PRs to help: tauri-apps/cargo-mobile2#493 tauri-apps/cargo-mobile2#495