Passing values between activities properly

Question

Hello I am new to android and I have a problem I do not know how to solve. I have 3 activities, ActivityMain, ActivityA and ActivityB. ActivityMain is the start activity. From ActivityMain the user can move to ActivityA, when they do that a value is passed from ActivityMain to ActivityA like this:

Intent i = new Intent(context, ActivityA.class); i.putExtra("eventId", eventId); startActivity(i);

And in my onCreate method of ActivityA I have an init() function that gets that value like this:

public void init() { this.eventId = Integer.parseInt(getIntent().getExtras().get("eventId").toString()); }

Now this is my issue, for some reason when I navigate from ActivityA to ActivityB then I click back my app stops working a Null Pointer Exception is thrown at the above line of code.

Check for null value for intent and the integer you are retrieving from intent — Suraj
– Suraj, Commented May 14, 2016 at 9:22
Not essential to the answer, but you should catch the NumberFormatException..... — Skywalker
– Skywalker, Commented May 14, 2016 at 9:24

takrishna · Accepted Answer · 2016-05-14 09:22:54Z

2

Cache the data from "Extra" to a variable - use onResume() method in your activity to set any configurations.

answered May 14, 2016 at 9:22

takrishna

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3 Comments

user3718908x100 Over a year ago

I can't understand though why onCreate() is called when I press back, is that how it's supposed to work?

takrishna Over a year ago

That is correct - Activity lifecycle has a hierarchy which gets followed - onStop is called when activity goes behind and returns - see here for more details - developer.android.com/reference/android/app/…

takrishna Over a year ago

One has to use "onResume" and "onCreate" handle that the OS provides - you could put a check ("if" statement) to determine whether an instance of your activity is already in the backstack and skip obtaining the "bundle" through getInt/getBoolean

Masum · Accepted Answer · 2016-05-14 09:29:49Z

if you pass integer try something like this

this.eventId = getIntent().getExtras().getInt("eventId");

or if you pass string. try this

this.eventId = Integer.parseInt(getIntent().getExtras().getString("eventId"));

PEHLAJ · Accepted Answer · 2016-05-14 16:13:01Z

0

The problem is you are passing data to intent directly and trying to access it from intent bundle but not intent. Use intent.getIntExtra("eventId")

Replace:

Integer.parseInt(getIntent().getExtras().get("eventId").toString());

With

eventId = getIntent().getIntExtra("eventId");

Secondly if you eventId is integer then use intent.getIntExtra, if eventId is string then use intent.getStringExtra

edited May 14, 2016 at 16:13

answered May 14, 2016 at 9:29

PEHLAJ

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3 Comments

user3718908x100 Over a year ago

Thanks, I saw no "getInt()" function though, there was getIntExtra and it took two parameters.

PEHLAJ Over a year ago

So you have that reason not to accept the answer ;) It's ok

user3718908x100 Over a year ago

That didn't solve my problem though, looks like the issue wasn't with how I was passing the value but the activity getting destroyed when I moved to the next activity to conserve memory so whenever I navigated back onCreate was called first instead of onStart.

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