Develop Reference

Design of RecyclerView program in Android

I'm working on my first app that uses RecyclerView and while I am making great progress, I strongly suspect that my design needs some changes.
I've asked in several places over recent weeks for complete examples of a RecyclerView that read, update, insert and delete and have come up empty so I'm guessing my way along based on various passing remarks. First, let me explain concisely how I have designed this app. I imagine this will make my mistakes self-evident.
My RecyclerView is based around sales in the small company where I work. Each sale consists of a client code, an order number, an order date, a number of tickets sold, and a seller name. My design uses a listener to react to a FAB (FloatingActionBar) and, if pressed, goes to an Add activity that prompts the user for the information needed to create a new sale. No information is passed to this activity because none is needed. The Add activity validates the data and, when the user presses an Add button, that new data is passed back to my main activity. The main activity inserts a row into a remote MySQL table via a PHP script invoked from an AsyncTask in my app. Upon returning from the database, if the insert worked (it could fail if it was a duplicate record), I add the information to my ArrayList and notifyItemInserted in the onPostExecute() method. That all seems to work okay although I always get two copies of the new sale in the RecyclerView. The next time the screen refreshes though - when I do another Add, Update or Remove - the duplicate sale disappears.
Each item in my RecyclerView contains all of the information for one sale, plus two clickable images, one intended for Editing (it's a blue pencil), and one intended for Remove (it's a red garbage can). If the user wants to edit that sale, he clicks on the blue pencil; if he wants to delete it, he clicks on the red garbage can. I use listeners to determine which image got clicked.
When someone clicks on the Edit graphic, I launch an Edit activity, passing the information from the existing sale to that activity. The activity displays the information and the user can modify any of the five fields. All changes are validated and, if all the validations are successful, the changed information is passed back to the Main activity which updates the existing row in the database in the doInBackground() method of an AsyncTask. If the update is successful, I try to change the information in my ArrayList and notifyItemChanged in onPostExecute(). That always fails.
When someone clicks on the Remove graphic, I launch a Remove activity, passing the information from the existing sale to that activity. The activity displays the information and the user can only press Remove to confirm that the sale should be removed or press Cancel to abort the removal. If Remove was pressed, the information from the sale is passed back to MainActivity which removes the existing row in the database in the doInBackground() method of an AsyncTask. If the database delete is successful, I try to delete the item from the ArrayList and then notifyItemRemoved in onPostExecute(). That always fails.
As you can see, the Edit and Remove both fail every time. The reason is that there is an indexOutOfBoundsException with respect to the position used in attempting to modify or remove the item from the ArrayList.
Now that I've set out an understanding of the situation, I can ask my specific questions:
Is it reasonable/appropriate to use Activities to do the work I've described for Add, Edit and Remove processes in the first place or would I be better making them fragments?
Is it appropriate to be doing the database activity and the adjustment of the ArrayList in the main activity or should I be letting the Add, Edit, and Remove activities (or fragments if that's better) do the work?
I think my fundamental problem is that my code can't "see" everything it needs to see at the point where it is doing its work. I think I need to redesign things a bit to make the app work better.
RecyclerView seems to be pretty fundamental so I want to make sure I write everything correctly. In fact, given the absence of good examples that show a RecyclerView that has all the functionality I'm describing, I'd like to write a tutorial or make a video series showing my finished app with all the critical parts explained so that others can learn from it.

Android app - Information screen

I'm developing an android app that is going to be used on a information screen. This app contains 5 (weather, next run, opening hours, etc...) activities, the plan is to loop through these activities with a timeinterval. So it starts with first activity, sleeps for like 5 seconds and then jump to next activity, and when it comes to the last activity, it should start in the front again.
What is the best solution to create a navigation system like this? Have Android some special features for things like this, or is the default startActivity() the only way?
And there is a little twist with this, some of the activities needs to retrive data from external sources by HTTP. So the activities must be done with data-query before it starts the activity.

You use startActivity to swap between activities. After you are finished with an activity, remember to call finish() - otherwise there will be a lot of instances of the same activity.
But if you want something like an information screen, you could use a single activity but use Fragments. That way you simply inflate a single fragment, and keep a timer to swap between them. You can still show the same content, but there are some differences between activity and fragment in inflating and finding the views by id.

closing an activity using finish(); wont make app start fresh in next run! why?

I wondered if anyone can shed some light on this,
I have one activity app which has a listview. In onCreate() I populate some data in that listview (reading it from sqlite database). I have a close button which triggers finish(); too. now when I press close button, activity disappears but when I click on app icon on desktop (or selecting it from phone history button) I see all previous data in the listview. the function that I am looking for is to start app fresh after clicking close button for next run. (something like banking app log-out button). (list view here is only an example to put across the need, so clearing list-view before finish(); is not acceptable. It is very simple and plain request and I do not think any code is necessary but if anyone interested I will post some code too.
What I want is same behavior as a banking app in exit, when user leave the main screen or click sign out, the App closes altogether. I can achieve this by using following methods (number 2 and 3) but apparently these solutions are not best practices. Then what method a banking App uses to close the app instantly? I doubt they use something which is not best practice such as System.exit(0)?! or do they!
Many developers claiming closing an App or killing parent activity
is OS job
Some say use use :
int pid = android.as.Process.myPid();
android.os.Process.killProcess(pid);
(this solution according to this is not a good idea because in next run app acts like it has been crashed last time https://stackoverflow.com/a/24015569/4173238 )
some say use System.exit(0); according to this
https://stackoverflow.com/a/5846275/4173238 is not recommended either
some say use finish(); but finish does not do what I want
Thanks for any input

If you have a mechanism that allows it so that you only deliver messages to the main thread when the application is resumed, then you can register your activities on an event bus like Otto and send an event that every Activity is subscribed to on which they call finish() on themselves.
Another possible solution is starting every activity with startActivityForResult(), and if you click the exit button, then you would say
public static final int KILL_ACTIVITY_RESULT_CODE = 0xD34DB33F; //why not
public boolean onOptionsMenuItemSelected(MenuItem menuItem) {
if(menuItem.getId() == R.menu.kill_activity) {
setResult(KILL_ACTIVITY_RESULT_CODE);
finish();
}
}
#Override
public void onActivityResult(int requestCode, int resultCode, Intent data) {
if(resultCode == KILL_ACTIVITY_RESULT_CODE) {
setResult(KILL_ACTIVITY_RESULT_CODE);
finish();
}
}
}
...and one time I've seen someone make static references to every single activity they had, and called finish() on each and every one of them. But don't do that, that essentially means you have failed as an Android programmer, and there is nothing to redeem you of your sins.

As brilliant CommonsWare, has pointed out in his comment "Static" was the issue! I was using static variables to store data to fill My listView. Apparently even if you have only one Activity and close it, Static variables remain intact! on app re run!
If you asking why I used static variable at the first place, I have to say, right or wrong, I wanted to share that variable between my other java class (my databaseHandler.class).
Why Android not clear all (including static variables) resources when closing the main and only Activity of app, remains a question and this is my next reading topic! but many thanks for anyone who post a comment on this question,
I will also change the question from:
How Banking Apps close? finish() does not do the same job for me
to
closing an activity using finish(); wont make app start fresh in next
run! why?

Prevent screen display until after fetching data

Is there any way I can go from one activity to another and delay the display of the screen on the target activity?
What I want to be able to do is to allow the target activity to fetch its required data but not to display anything until does.
I want the screen of the source activity to still be visible until I am ready with the data in the second activity.
Specifically, I am using an AsyncTask to fetch the data.
I know I could fetch the data in the source activity and then send it on to the target activity but this is not viable in our case.
Edit: More Info:
The whole reason I want this is because I am trying to change the structure of certain parts of the current code.
At present the way it works is the the first activity gets the data and then sends it to the second activity as a bundle.
This created problems when the second activity could be invoked from multiple places. It resulted in loads of duplicate code.
So, I decided to move the fetching of the data into the target activity thus cutting out any need for repeating code.
it also makes more sense for the activity to fetch its own data rather than relying on something else sending it.

You should first make a service that runs your async task. Then, start the service from your first activity with startService(new Intent(this, UpdaterServiceManager.class));
When the task ends in the service, start the second activity.
Click here for an excellent service tutorial.

Try to use service for this purpose.

Best way to terminate a wizard in android

I have a reservation wizard in android, when i say wizard i mean i have multiple activities (meaning screens) that are passed from one to another until booking is complete. in each step of the way my info may be invalid and so ill have to back track 2-3 activities and start all over, all the activities i back tracked should be destroyed, they may need to invalidate a singleton data container that they filled with their data.
I thought of 2 ways to do this:
start all activities related to the wizard with startActivityForResult() so i get notification when an activity is finished and with which error code (finished OK or error occurred) and act accordingly (for instance: if in the middle an activity fails it will return failed and the previous one will return failed as well until i get to the wizard's first activity where i either declare the error with a dialog or show the 'thank you' screen.)
I can send an react on intents with certain parameters so i have a 'close and clean' intent message that close down the previous activity etc...
which way is better, any other interesting\efficient way to do this ?

I Got a hint that got me thinking in a different direction:
use an invisible Activity, or alternatively , a local service,that is the 'brains' that known on each turn of the way what action is to be taken. to remove a complete stack of unneeded activities i should use the FLAG_ACTIVITY_CLEAR_TOP on the bottom most activity i want to use next.
Another options is to enclose all
the activities i want to play with
their pposition on the stack inside
an ActivityGroup Object which keeps
all activities alive (like in Tab)
and on the stack, but you control
which one is displayed and which is
not. the activity group will contain
the state machine logic regarding
which Actvity should not be
displayed and which should be
disposed.