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I would like to pass data from activity to service. Currently I am trying to use an ArrayList<HashMap<String, String>>. What options do I have for passing this to the service? I was thinking about putting it as extra data in the intent but I'm not sure how to do this. Or is it possible to have this set up as some sort of global?

At the moment it is set up as a static of the activity, and the service is calling back to the activity to be provided with the next item from the ArrayList. I'm not happy with how that is working, so would like to move the list into the service.

EDIT

In response to the questions raised below:

I am trying to pass a playlist (yep, another media app) to the service. The playlist ArrayList<HashMap<String, String>> contrains paired song info, such as "songTitle" , "this is a title".

I think however that i am getting confused with the lifecycle of the application. When a user clicks play, the service is created. If I used a static for the list, when the service is created it would see that list. So the service will happily continue to play songs from this list. However, if the user changes folder etc, how do I get the app to recognise the change in playlist? The way the app is designed, the user can untick tracks in the list at any time, or can browse to a different folder. When the song completes the new list should be loaded. What is the best way of doing that? Or is the way that I am doing it now the best way? When the song completes send a broadcast back to the main activity requesting the next track. Should I destroy the service at this point and allow the "next song" function recreate it?

Lifecycle confusion!

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What kind of data are you trying to pass to the service? The array of hashmaps? – SemperFly Oct 23 '12 at 21:40
If you implement a Parceable object you can put it as an extra in the intent- correct? Cant you do that? – Sajit Kunnumkal Oct 23 '12 at 21:40
Assuming that you're done editing the arraylist by the time the service gets to it, Did you try importing the static variable instead of simply calling it? – mango Oct 23 '12 at 21:45
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2 Answers

up vote 1 down vote

Both ArrayList and HashMap implement Serializable, so you should just be able to stuff your structure in an Intent, and retrieve it using Intent.getSerializableExtra().

From your Activity, all you need to do is call the Intent.putExtra(String name, Serializable value) overload.

As a rule of thumb, try to avoid having static variables hanging out in your application if possible. They get tricky when your app is shut down by the OS and then recreated (i.e. from the recent apps list).

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Yes, I agree, I want to avoid statics as much as possible, which is why I was hoping for a better way of passing data. In order to pass the serializable data, will I need to have a custom class that writes this, or can I just throw the ArrayList at it at the appropriate moment? – Adam Sherratt Oct 24 '12 at 7:02
See my updated answer. All you need to do is pass the ArrayList to intent.putExtra(). – wsanville Oct 24 '12 at 13:29
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up vote 1 down vote

Have you considered storing the data in a database and simple sending the intent that data has changed? Or use a ContentProvider that signals "by itself" that data has changed and needs to be reloaded? That way you won't use state even if the app closes unexpectectly.

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I hadn't considered that, but its not something I've done before. Could I trouble you to talk me through the lifecyle? I'm thinking: create playlist, save to database. Click play, start service. Service checks database for content, plays track 1. On next/complete plays track 2. If user changes playlist, how does the service know? How does the activity know that song 2 has started? – Adam Sherratt Oct 24 '12 at 7:51
You would trigger the service with an Intent, containing e.g. an enum NEW_PLAYLIST, START, PAUSE, ... The service could signal song completion by means of a (local) broadcast, that is then handled in the Activity. I still have to try that in detail myself. – koljaTM Oct 24 '12 at 12:23
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