Support use across multiple processess, how to use it? about tray HOT 3 CLOSED

IPC for multiprocess support

To share data between two processes you need inter-process communication (IPC).

A common android example for this are SyncAdapters which run on different processes than your UI. When you want to trigger an action in the UI from your SyncAdapter you can't simply call a function of your activity you need to use IPC. When you use the SharedPreferences in the SyncAdapter you are able to save the data. But the UI (in a different process) uses a different SharedPreferences object and does not receive a data change. Even worse, if you read the value written in the SyncAdapter from the UI process you get the old value for some seconds. (issue on StackOverflow)

Implementing Binder for IPC is hard and low level. But ContentProviders do IPC out of the box. That's why a ContentProvider is used to support multiple processes.

Why a database

A ContentProvider doesn't mean the data is written to a database. It's just a interface which supports CRUD operations. And those operations are process save. Yes, Tray is using a sqlite database under the hood but if would be possible to swap out this implementation and save the data to any other persistence framework. This works because the ContentProvider would use the same persistence Object for all operations. But the multi process support would only be guaranteed when you access the data with Tray and the ContentProvider and not directly with the other persistence frameworks.

So ContentProviders makes CRUD operations multi process save.

The Sqlite database is used to store the data. It's no just a simple key value store (like the shared preferences) because you can get additional informations for every key value pair saved to Tray automatically. You can get informations when the data was saved first or when the data was last updated. (see here).

ContentProvider facts

• The ContentProvider used is only accessible from your Application.
• You can override this permission in your manifest to make it public accessible.
• If you want you can access the data in the ContentProvider directly with getContext().getContentResolver().insert(uri, values);. This means Tray is just a high level abstraction to access the data in the ContentProvider.

Tray is not async

Tray doesn't support asynchronous operations. Everything runs synchronous. A mPrefs.put("key", "data"); immediately writes the data into the database. If this function returns the data is saved to disk.

It's up to the developer where to save the data, inside the UI Thread or in a worker thread. In my cases this was never a problem because I was writing data in a non-UI process where I didn't have to care about frames.

I hope I could help you understand this lib 😄!

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so now everything is clear.

I propose to describe(copy your text) it on the main page or in the documentation

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I have a question，when a call mPrefs.get("key") on the ui thread, and it is synchronous, will it block the UI thread when the data is so big?

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