Kotlin - How do i set a sharedpreference code so that i open the closed app, it opens the last Activity, where i left it - kotlin

Question

I made two activities in my application, I want the app to be opened where I left off. In other words, not the default activity but the activity where I was when I last exited the app.

Answer 1

You could set a SplashActivity, where your app start, that will start other activities.
In this SplashActivity, you can set a var lastActivity, that will be a code to keep in which activity you were last time.
You get it with SharedPreference, and then go to the activity.
i.e :
String lastActivity = SharedPreference.getString(...) // I don't really remember the syntax
if (lastActivity == "HelloWorldActivity")
startActivity(HelloWorldActivity.getStartIntent(context))
else if (lastActivity == "GoodByeActivity")
startActivity(GoodByeActivity.getStartIntent(context))
Then, do NOT forget to edit your SharedPreference value EACH TIME you change activity.
I don't know if this is a good practice, but feel free to test this and give your think.
EDIT
First, you need to understand how is Shared Preference File. I think it looks like this :
"app_name"="Your app name"
"last_activity"="Your last activity"
"user_age"="23"
This could be the first activity you launch :
class SplashActivity : AppCompatActivity() {
var lastActivity = ""
override fun onCreate(savedInstanceState : Bundle?) {
super.onCreate()
/*
Here, we will get the SharedPreferencesFile.
Then, we get the value linked to the key TAG_LAST_ACTIVITY (set in companion object)
*/
val sharedPref = this.getSharedPreferences(getString(R.string.shared_preference_file_name), 0)
lastActivity = sharedPref.getString(TAG_LAST_ACTIVITY, "")
var activityToStart : AppCompatActivity? = null
if (lastActivity.isBlank())
activityToStart = YourActivityToStartAtFirstLaunch.getStartIntent(this)
else if (lastActivity.equals(TAG_ACTIVITY_ONE))
activityToStart = ActivityOne.getStartIntent(this)
else if (lastActivity.equals(TAG_ACTIVITY_TWO))
activityToStart = ActivityTwo.getStartIntent(this)
else if
... // Use as many as else if you need, but think about the "when" condition, it is better !
startActivity(activityToStart)
}
companion object {
private const val TAG_LAST_ACTIVITY = "last_activity"
private const val TAG_ACTIVITY_ONE = "activity_one"
private const val TAG_ACTIVITY_TWO = "activity_two"
}
}
And this could be your ActivityOne, for example :
class ActivityOne : AppCompatActivity() {
override fun onCreate(savedInstanceState : Bundle?) {
super.onCreate()
/*
Here, we will modify the variable LAST_ACTIVITY in the shared preferences file by setting it to "activity_one".
So, if the user quit this app now, you will know at next launch in which activity he stopped.
I think it is a better practice to set this in the onPause() or onStopped() method. Think about it ! ;)
*/
val sharedPrefEditor = this.getSharedPreferences(getString(R.string.shared_preference_file_name, 0)).edit()
sharedPrefEditor.putString(TAG_LAST_ACTIVITY, TAG_ACTIVITY_ONE)
sharedPrefEditor.apply()
}
companion object {
fun getStartIntent(context : Context) : Intent = Intent(context, ActivityOne()::class.java)
private const val TAG_ACTIVITY_ONE = "activity_one"
private const val TAG_LAST_ACTIVITY = "last_activity"
}
}
Do not forget to put your shared preference file name in your values/strings.xml file :
<string name="shared_preference_file_name">com.example.yourappname.sharedpref"</string>