Develop Reference

Proper data transfer between activities

I have few questions about passing data to another activity. Let's say I have three activities I called them
first activity
second activity
third activity
When app is enabled by user, the user is in the first activity. To go from the first activity to the third activity user must also go through the second activity. The workflow
first activity (user push button) ->
second activity (user push button) ->
third activity
Let's assume I need data from the first activity in the third activity, so I need to pass my HashMap with my data from first activity to the second activity and then to the third activity?, is there any way to pass data directly from first activity to third activity but like I said, user has to go also through second activity.
I'm doing this in that way...
Intent secondActivity = new Intent(this, secondActivity.class);
secondActivity.putExtra("myHashMap", dataHashMap);
this.startActivity(secondActivity);
then in the second activity I have this part of code
secondActivity = getIntent();
dataHashMap = (HashMap<String,
String>)secondActivity.getSerializableExtra("myHashMap");
and then I'm repeating this upper two steps for the third activity. Is this correct way? because looks a little bit confusing and time consuming. Also there is another problem, now if I am in the third activity and I want to go back to the second or first activity I have always pass some HashMap because activities expects this type of data. Is there a way to sometimes return to a previous activity but no longer pass any data (HashMap in my case) if it is not needed?.
secondActivity.putExtra("myHashMap", dataHashMap); //- I would like to sometimes skip this step
I tried to this code below to handle with this but it does not work, my app keep stopping/crashing because second activity expects hashMap data from the third activity.
secondActivity = getIntent();
if(secondActivity != null){
dataHashMap = (HashMap<String,
String>)secondActivity.getSerializableExtra("myHashMap");
}
Thanks for answers, regards.

You can use a variable that is placed inside Application class instance. This variable is shared for all activities and other elements of the application.

You have several options. Firstly, you said in a comment that you only need one element. In that case you can just pass the one element as an "extra" in the Intent, instead of passing the entire HashMap.
Secondly, I don't understand why you return from the third Activity to the second Activity by calling startActivity(). You should just call finish() and that will return you to the second Activity.
If you need to return some data from the third Activity to the second Activity, you should start third Activity using startActivityForResult() and set the data to return in third Activity using setResult() and the data will be returned to second Activity in onActivityResult().
Another option is to do it exactly as you have done it, but also copy the hashMap into the Intent as an "extra" each time you call startActivity(). If you only have a handfull of entries in the hashMap it won't make any noticeable difference in performance.

How to kill particular activity from task?

In my application I have 6 activities like 1->2->3->4->5->6. In 6th activity user can choose any activity(I am launching with intent). Means he can choose 1 or 2 or 3 or 4 or 5. Now when I press back button it is coming back to 6th activity again(which I do not want).
ex:
I have executed like this 1->2->3->4->5->6. Now I am in 6th activity. Here I have button, when I press it, it launched 4th activity. My code is like this on button click.
Intent intent = new Intent(MainScreen.this, UniversitiesScreen.class);
startActivity(intent);
So now I am in 4th activity. When I press back button it taking me to 6th activity(which I came from) instead 3rd activity(what I am expecting).
Can any one help me to handle this type of navigation.

Simple answer is edit your onBackPressed method in every activity...
For example, Write in 4th activity like this
#override
public void onBackPressed(){
Intent in = new Intent(this, ThirdActivity.class);
startActivty(in);
finish();
}
Please check the context that you are passing to intent. Every activity is different so pass the activity context from where you are calling another activity.
If my guess is true Mainscreen.this is first activity, and if you call fifth activity from fourth activity, give intent as
Intent in = new Intent(FourthActivity.this,FifthActivity.class);
startActivity(in);
finish();
And you are not saving any data in backstack and you are going back manually...

The best way is to use the NavUtils.navigateUpFromSameTask(this) function in your activity. For this you need to define the parent activity in the manifest for each activity so when you are in the 4th activity then the parent activity is the 3rd activity.Then when you click on back or navigate up you end up in the parent activity i.e. from 4th to the 3rd.
Take a look at this
http://developer.android.com/training/implementing-navigation/ancestral.html
Look at the manifest and then the Navigate up to parent task section
This will also help in returning to the same state of the 3rd activity from the 4th activity.

How to get back to the first activity when opening multiple activities

I have an app which have HomeActivity and 4 activities A,B,C,D.
I want when clicking on button start_activity_A_btn in HomeActivity to star activity A, and A starts B, B starts C, C starts D, then done button which takes me to HomeActivity.
NOTICE : in every activity (A,B,C,D) I have some data to save and get back to the HomeActivity after pressing done button.

What you need to do use the following flag in your intent (please check the link, it explains a similar situation to the one you are facing): FLAG_ACTIVITY_REORDER_TO_FRONT. So, in your activity D, in the onClickListener for the done button, here's the code you'd have to use:
Intent intent = new Intent(this, ActivityAname.class);
intent.setFlags(Intent.FLAG_ACTIVITY_REORDER_TO_FRONT);
intent.putExtra("data", dataYouReceiveFromABCD);
startActivity(intent);
This will get your A Activity to resume.
Now, regarding the "data" you will just have to keep accumulating this data in a String using some separator if that's possible (since you haven't told us what this data is exactly), so if it was a username and a password you could separate the two using a random combination of characters that will possibly never occur ("246#$^") and then just keep creating a string that you keep building in A, B, C and D and then finally in D you put that String as an extra in the intent (check the code I've posted above). If it's some other sort of data then you could perhaps serialize it if that helps. However, if you do use a String with a predetermined separator then all you will have to do is in Activity A you will have to use the following code in the onResume() method of Activity A.
if(this.getIntent().getExtras().getString("data") != null)
{
String data = this.getIntent().getExtras().getString("data");
//do some stuff here with that data
}

If you need data returning an Activity, you should use startActivityForResult to start ABCD. This works very much like your HomeActivity is opening up some dialog, and once the Activity finished (by pressing done or cancel, depends), you get onActivityResult in your HomeActivity.

From within an android activity test, how do I finish another activity that my main activity started?

I am writing an activity test for an activity we wrote with 3 buttons. 2 of these buttons start other activities.
I can write a test that simulates a button push and then checks if the desired activity is running, but I can't move back from that second activity. The second activity stays at the front and prevents the other tests, that assume the first activity is running, from working properly. They just kind of freeze.
I have a reference to the first activity, but it is the second activity I need to I guess call finish() on. Is there a way to do this?
EDIT: I added some actual source code illustrating my problem in this gist: https://gist.github.com/3076103
It is specifically about testing activities. In the production code everything is fine.

You should probably use http://developer.android.com/reference/android/app/Instrumentation.ActivityMonitor.html to get a reference of the second activity or you can block the second activity from being launched(Still you are guranteed that the call to start the second activity infact had reached till the framework).

You need a way for your activities to communicate with one another, so that one activity can tell the other to finish. There are several ways you can accomplish this. One method is to create a service within my application; my "second" activities would connect to this service to register a way to receive messages, and my primary activity would connect in order to provide them.

In Activity1 add the following to start Activity2
Intent myIntent = new Intent(view.getContext(), Activity2.class);
startActivityForResult(myIntent, 0);
In Activity2 add the following to start Activity1 and finish Activity2
Intent intent = new Intent();
setResult(RESULT_OK, intent);
finish();
For more details: http://www.warriorpoint.com/blog/2009/05/24/android-how-to-switch-between-activities/

If you start the activity using startActivityForResult, then you can close the activity from parent using finishActivity(int requestCode).
To start the activity :
startActivityForResult(new Intent(...), 123123 /*requestCode*/);
And when you want to finish that activity (from caller), use :
finishActivity(123123 /*requestCode*/)
Also there is a way to find, whether child activity is finished or not. But you can track this only when child activity calls finish() for self. To receive the child finish request from the child, you need to override the finishFromChild() method in parent activity.

OnClick restartActivity?

How can I restart An Activity on click?
For exemple: I have got in my AndroidManifest.xml 2 activities the activity A and B and they start when application starts...
But what I want is when I click in a button that is on Activity A it must restart activity B.

when you are in activity A, and proceeding to activity B, then your activity B automatically starts/re-starts

Why do you need to start both Activities on starting your app? When you say "restart", do you actually need to stop Activity B and start Activity B again? Or do you just want to show it? To start an Activity from another Activity, you could call something like this:
startActivity(new (Intent(this, ActivityB.class)));
The Android documentation gives plenty of detail. However, I think you should consider why you are starting two activities at once, and whether you might want to use a Service instead (not knowing any details of your app, I can't say).

Intent intent = new Intent(CurrentActivity.this, ActivityToLaunch.class);
startActivity(intent);
call above piece of code on onClick of view method.