This is VolButKill, essentially elesbb's "Hold Back to Kill", but worse.
The upside is, it works for devices that do not have a physical back button.
The downside is, it does not use the back button, physical or not.
Instead, the volume buttons are abused to achieve a similar purpose.
The procedure is a bit more involved and less intuitive than in HBTK:
1. Press both volume buttons at approximately the same time (within 250ms
of one another). Release both buttons. This "arms" the kill logic;
the phone will confirm it with a brief vibration and a toast message.
2. For the next 10 seconds, both volume buttons are assigned new functions:
- Holding volume up for 1 second will kill the foreground app
- Pressing volume down will disarm the kill logic early and restore
normal behavior
The 10 second timespan is chosen for phones that produce some action for
pressing both volume buttons (like older LG phones launching QuickMemo),
so there is enough time to get the to-be-killed app back to the foreground.
It was considered to avoid the whole arm/disarm logic and kill on holding
both buttons for a set duration, but that makes it difficult to quickly
put away any QuickMemo-like apps popping up, and it also activates some
accessibility feature like talkback on other phones.
It was considered to kill upon, say, holding volume up for a while and
then tapping volume down, or vice versa. But that sucks as well, nobody
wants their ring volume changed every time a misbehaving app needs to go.
Therefore, arm-then-kill it is.
Notes and caveats:
- The minimum required API level for VolButKill is 18, corresponding to
Android 4.3.x (Jelly Bean). It has been confirmed to work
on 4.4 (KitKat) and 8.0.0 (Oreo). Feel free to report back other
versions you've tested it on.
- All the delays, as well as the button sequences are hardwired; there is
no configuration-like activity. This is /just/ a naked accessibility
service. After installing, it has to be enabled in the accessibility
submenu inside the phone settings before it will work.
- It (obviousy) requires the phone to be rooted. It has been tested with
Magisk as well as with an ancient version of SuperSU; it should work with
anything that provides a 'su' and a 'killall' program.
- VolButKill will try to avoid killing the "Home" screen. If the app name
of your launcher is not "Home", that will not work. Feel free to drop
me an email to get your launcher app added to the do-not-kill list.
- VolButKill will try to avoid killing keyboard apps. Due to the way the
foreground app detection works, if the foreground app has its focus on
a widget that causes a keyboard to be displayed (like a text input field),
the actual foreground app is actually the keyboard itself, so what would
be killed is the keyboard, not the app itself. In order to avoid this
situation, VolButKill will ignore any app that has the string 'keyboard'
in its package name. There probably exists keyboards with offball package
names that will be missed; if you encounter your keyboard being killed
drop me an email to add your keyboard app to the do-not-kill list.
"Hold Back to Kill" did not suffer from this issue because it detected
the foreground app in a way that Android no longer supports as of more
recent versions.
- VolButKill is implemented as an accessibility service, but does not
actually provide accessibility features. This is a big Google No-No.
For this reason it will never be allowed on the Google Play Store.
Any attempt to submit it will only fuel Google's hate boner for people
using accessibility services for features they weren't designed to do
and make life more difficult for everybody doing this.
- VolButKill is Free and Open Source Software, licensed under the 3-clause
BSD License. Feel free to copy/modify/share/whatever VolButKill as
long as you credit the original author and keep the license terms intact.
Look at the bottom of this file for details.
- I don't usually write Android apps, and for all I know I did every single
thing wrong and violated every design and programming guideline in
existence. If you're an experienced/knowledgable Android programmer and
reading the source, feel free to report things that seem off/wrong.
- You can contact me at <fstd+vbk@pr0.tips> or on #fstd on irc.freenode.org
Copyright (c) 2020, Timo Buhrmester
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