Problem
Throughout my app I need to download files. In some cases I only need one-way communication, basically communicating with the Activity that a download has finished. In other cases, I need to be able to communicate to the background process to cancel the download, then relay back to the Activity once that task has been complete (two-way communication).
Stipulations
In all cases, a download is only associated with one Activity, so a Service seems unnecessary since I don’t need to keep a download running in the background while the user does other things. The user is always blocked while the download is occurring. The download process should be Activity-independent (not specialized for one Activity…reuseable). It would be ideal to have one solution that meets all requirements.
Use cases
The two cases I have right now are as follows:
- A user is shown a
ProgressDialogwhile a file is being downloaded. Once the file completes downloading, the user proceeds to the next Activity. Progress does not need to be shown. - A user is shown a
ProgressBarwhile a large file is being downloaded. There is a Cancel button to abort downloading the file. Pressing the Cancel button should signal to the background process to abort downloading the file, then inform the Activity once that action has been performed. Progress needs to be shown while downloading the file.
What I’ve tried
My original implementation was a separate class, ran in a thread, that passed in a Context that would broadcast progress. This allowed communication from the background process to the Activity, but not vise-versa.
I attempted a Service, but from various articles I read, determined my needs did not justify a Service, as the user needed to be blocked while the download was occurring. I had never implemented a Service before, so I also ran into communication problems (probably poor implementation).
What would be ideal
A two-way BroadcastReceiver. Is that possible? I like being able to register for a BroadcastReceiver if I want to get feedback from the background process, or not if I don’t care. I already have a method in a class that takes in an InputStream and a File and makes the transfer, so that method is being reused everywhere that needs to download a file right now.
Besides AsyncTask, you can also use Loaders.
They do pretty much what you need to do and I think they are available since android 1.6 with android compatibility package [related post]. I think this is your best option 🙂