Having trouble with hardware back button for an Android build

Getting Started Newbie Questions
#1

Having trouble with a hardware back button for my app.

Everytime I press it - it closes the app both in the simulator and test device.

I’m following this older tutorial for key processing and updated it for composer

https://coronalabs.com/blog/2013/03/26/androidizing-your-mobile-app/

and added a bunch of prints to help troubleshoot whats going so wrong here.

local publicClass={} publicClass.onKeyEvent= function ( event ) local composer = require( "composer" ) local phase = event.phase local keyName = event.keyName print( event.phase, event.keyName ) if ( "back" == keyName and phase == "up" ) then if ( composer.currentScene == "splash" ) then print(composer.currentScene) print("Splash screen Close") native.requestExit() else if ( composer.isOverlay ) then print("close overlay") composer.hideOverlay() else local lastScene = composer.getSceneName("previous") local currentScene = composer.getSceneName("current") print( "previous scene name is", lastScene ) print( "current scene name is", currentScene ) if ( lastScene ) then composer.gotoScene( lastScene, { effect="crossFade", time=500 } ) else native.requestExit() end end end end if ( keyName == "volumeUp" and phase == "down" ) then local masterVolume = audio.getVolume() print( "volume:", masterVolume ) if ( masterVolume \< 1.0 ) then masterVolume = masterVolume + 0.1 audio.setVolume( masterVolume ) end return true elseif ( keyName == "volumeDown" and phase == "down" ) then local masterVolume = audio.getVolume() print( "volume:", masterVolume ) if ( masterVolume \> 0.0 ) then masterVolume = masterVolume - 0.1 audio.setVolume( masterVolume ) end return true end return false --SEE NOTE BELOW end return publicClass

Maybe I’m not removing the eventHandler correctly

In the console   I’ll get a notification that the previous screen loads but then in immediately closes the app.

So if I’m on the menu scene and press the back hardware button

In the console I can see it shows  splash.lua but then the app closes.

If  I go a few more levels deeper ex. level1

I press the button once i get multiple out put in Console from printing the keyPhase

>down

>down

>up

then it immediately goes back to menu scene

and then back to my original (level1) scene and closes the app. almost instantly

I dont think my Event Listeners are stacking and maybe I’m not removing them correctly.

I got the info on adding the Event Listeners from an older similar thread which i didnt want to bring back from the dead

but it’shere for reference

--scene:show -- phase == did &nbsp;local keyhandler = require("keyhandler") &nbsp;Runtime:addEventListener("key", keyhandler.onKeyEvent) &nbsp; --scene:hide -- phase == will Runtime:removeEventListener("key", nil)

Any help or links to a tutorial on handling Event Listeners properly would be great thanks!

Even if I remove  native.requestExit() from my code the back button still shuts down the app completely.

#2

Hi,

you should return true to tell the system that you have processed an event.

Something like this :

 if ( lastScene ) then composer.gotoScene( lastScene, { effect="crossFade", time=500 } ) return true else native.requestExit() end
#3

Thanks!  Thats perfect and keeps it from exiting the app.

In addition to that I think I was too focused on the app exiting hardware part and  I also didn’t realize that my code still creates a “previous” scene endless loop. 

For anyone else researching this… had to go back and create a custom history as described in the first tutorial.

#4

Hi,

you should return true to tell the system that you have processed an event.

Something like this :

 if ( lastScene ) then composer.gotoScene( lastScene, { effect="crossFade", time=500 } ) return true else native.requestExit() end
#5

Thanks!  Thats perfect and keeps it from exiting the app.

In addition to that I think I was too focused on the app exiting hardware part and  I also didn’t realize that my code still creates a “previous” scene endless loop. 

For anyone else researching this… had to go back and create a custom history as described in the first tutorial.