Close an Ionic Android app with back button

2/20/2020

Ionic documentation is good, but it's not very extensive in some topics. One of them is, for now, the React integration in mobile platforms.

In the case in point, handling Android's back button to close the app in a standard way. This issue doesn't affect iOS at all, since iOS devices don't have a physical back button and multitasking and app management work in a very different way.

The normal way of interacting with apps in Android is something like this:

You open an app and navigate to different pages
Every time you press the back button: go back to the last visited page in an app navigation, until you reach the root

page -or at least the first screen loaded when the app was loaded

You press back button again: either a toast message is displayed asking for a second back button press to confirm app

exit, or the app is closed directly

The default behaviour in Ionic React 5.0.0 is to navigate normally and using the back button to go back in window.history, but the app is never closed using the back button, you have to use the home or multitasking button to close it or switch applications.

I couldn't find a satisfactory answer on how to handle this using the React version of Ionic, even though I found many articles for Angular (some links below). Let's walk through the solution I put together:

Show me the code!

If you use Ionic React with the Capacitor Android integration, you have access to some APIs by default. One of them is the App API. You can use it to add listeners to some events, like backButton, that triggers a handler when the physical back button is pressed. You can also exit the app, which are the two tools we will need.

In my case, I will want users to go back to a single initial page in my Ionic app, so I only need to handle the back button event there.

The naive approach:

import React from 'react'
import { useIonViewDidEnter } from '@ionic/react'
import { Plugins } from '@capacitor/core'

const Home = () => {
  useIonViewDidEnter(() => {
    Plugins.App.addListener('backButton', Plugins.App.exitApp)
  })

  return <div>Content</div>
}

This will work in an app with only one page, but most apps will have some kind of navigation. Since we want to exit the app only when we are in that page, we should remove the listener when we leave the view. That's how we can do that:

import React, { useRef } from 'react'
import { useIonViewDidEnter, useIonViewDidLeave } from '@ionic/react'
import { PluginListenerHandle, Plugins } from '@capacitor/core'

const Home = () => {
  const backButtonListenerHandle = useRef<PluginListenerHandle>()
  
  useIonViewDidEnter(() => {
    backButtonListenerHandle.current = Plugins.App.addListener(
      'backButton',
      Plugins.App.exitApp
    )
  })
  
  useIonViewDidLeave(() => {
    if (backButtonListenerHandle.current) {
      backButtonListenerHandle.current.remove()
      backButtonListenerHandle.current = undefined
    }
  })

  return <div>Content</div>
}

We store the listener handle in the referencebackButtonListenerHandle when we register it on entering view, and when we leave we remove it in case it was set. That allows Ionic to handle back buttons going back in history and achieving our desired behaviour.

In case we have a modal or a different behaviour that requires only exiting app based on a condition, we need to add and remove the listener conditionally when that state changes. For instance:

import React, { useEffect, useRef, useState } from 'react'
import { useIonViewDidEnter, useIonViewDidLeave } from '@ionic/react'
import { PluginListenerHandle, Plugins } from '@capacitor/core'

const Home = () => {
  const [showModal, setShowModal] = useState(false)
  const backButtonListenerHandle = useRef<PluginListenerHandle>()
  
  const addBackButtonListener = () => {
    backButtonListenerHandle.current = Plugins.App.addListener(
      'backButton',
      Plugins.App.exitApp
    )
  }

  const removeBackButtonListener = () => {
    if (backButtonListenerHandle.current) {
      backButtonListenerHandle.current.remove()
      backButtonListenerHandle.current = undefined
    }
  }

  useIonViewDidEnter(addBackButtonListener)
  useIonViewDidLeave(removeBackButtonListener)

  useEffect(() => {
    if (showModal) {
      removeBackButtonListener()
    } else {
      addBackButtonListener()
    }
  }, [showModal])
}

I hope this helps!

/ blog

Roger Clotet Solé

Close an Ionic Android app with back button

Show me the code!

Further reading