Android StartActivtyForResult() from a Service

First I'm sorry for my english that is not so good :).

I am facing a problem to develop my app.

That is a general architecture scheme of my solution.

http://i.stack.imgur.com/ooTmE.png

To be quick, the app has to decode code bare but with two possible ways:

1. using exernal device (The constructor provides a sdk containing an android Service to communicate with the device),
2. use the camera of the mobile using the library Zxing which is possible to manage it with intent.

The goal of my own service is to manage some business code and make transparent the choice of the tool for the user.

I believed that was a good solution but I wanted to implement it and I had different problems.

My main trouble is that I cannot execute StartActivityForResult inside the service.

Do somebody have any suggestions for my problem whether a change in the architecture or a solution for the main problem?

@Laurent' : You have totaly right my service acts as an API adapter.

I will try to make the expected behaviour more clear.

I have an app that needs to recognize (real) objects which have QR codes on their top. This recognition action will be done several times by the user during the life of the app.

The user chooses to launch the recognition by clicking on a button (or otherwise but he knows that the recogntion will start). So no notification is needed.

The thing is he doesn't choose the way to do the recogniton. It is why, as you said, I implement an adapter.

The adapter chooses between :

Camera mobile or external device. The first is an activity coming from the Zxing library. The second one is a service that manages the external device. This service provides an interface to get back result.

One more thing, I need that my whole implementation (adapter and co) can be re-used by other apps that will also need to do recognition.

So my thought was to implement a service as an ada开发者_运维技巧pter to answer my two conditions (make transparent the choice for the user - and make the recognition available for other apps).

I hope you understand my problematic.

Given your architecture, your MyOwnService must act as an API adapter : it should provide a unified scanning API and address each external service specificities transparently.

Your expected behaviour is not clear enough to provide a solution that suits your needs but here are a few remarks that can be of some help.

Passive scanning:

• Even if there are some workarounds : no activity should be launched from a service (not directly). Never. Bad. Services are background stuff, the most they will be permitted is to hint users with Notifications (this is point 2 of Justin excellent answer).

As a consequence there's nothing as a 'popup Activities' (and that's good!). If you need to continuously scan for barcodes, even when your activity is not run, then the only way to warn users is by using status bar notification.

Active scanning:

• Inside your own activity you can bind to your wrapper service and make it start scanning for codebars. When it finds one it has to message your activity. Your Activity message handler has complete access to the UI to inform the user of your findings.

You selected Active Scanning in your edit, your problem is therefore to find a way for your service to actively notify your main application (the one that started the active scanning) that a new item has been scanned successfully.

You do NOT do this by starting a new activity (remember: this is bad) but you can bind to a service and/or use Messages between the wrapper service and the application.

I advice you take the time to read (and more time to comprehend) this android developer article on BoundServices and especially the part about Messengers.

A full example of Two Way Messaging between a Service and an Activity can be found in the following android examples : Service & Activity

Warning: designing robust, full blown AIDL-based services is a tough job.

Two ways you could solve this problem.

1) Have MyOwnService do a callback into MainActivity telling it to launch your ScanActivity. - This is a better approach if MyOwnService's task is only going to be running while MainActivity is running and if the user would expect the ScanActivity to come up automatically.

2) Have MyOwnService create a notification that will let the user access the ScanActivity. - This is a better approach if MyOwnService's task might be running longer than the life span of MainActivity. That way, you can let the user know, unobstrusively, that they might want to access the ScanActivity.

So finally I changed my architecture.

I make the choice to delete myOwnService and to create an intermediate activity that will be my API Adaptater.

This activity will have a dialog.theme to look like a dialog box indicating that a recognition is under execution.

If the recognition uses the external device this activity will stay at the foreground otherwise the camera activity will start (Being managed by the intermediate activity).

Thank to that I can manage my result from the intermediate activity and do not have an android strange architecture, keeping my business code for the recognition outside my main app.

Service was not the good choice.

Thanks a lot for you help and your time.