问题
I am using an Intent Service that performs an action and needs to pass back to the activity that started it the results of the action.
I've searched through dozens of similar posts but as far as i can tell, all solutions i found have a problem. They don't handle well screen rotation. Suppose an activity starts the Intent Service, the service takes 10 seconds to perform the action, and during those 10 secs, the screen gets rotated. The activity gets destroyed and a new one is created.
- Use Receiver : It creates a memory leak , as the receiver is bound to the activity that must be destroyed, so the activity never gets destroyed.
- Use Broadcast : You have to register a listener, and unregistered the listener before the activity gets destroyed. If the broadcast message arrives after the listener is unregistered, and before the new activity's listener is registered, the message will never be received.
- Use Messaging : Same as receiver.
- Use Shared Preferences/database with listener : Same as Broadcast.
The solution i came up with, is having the service save the result in a preference file, and the activity checking regularly (lets say every 200ms) for a change in the preference file. Thus, when the screen rotates, the activity stops checking, and starts again when recreated. If the result was delivered in between, it still gets to the (recreated) activity. However, it seems as though this consumes cpu and performs unnecessary reads from the SD card.
Another solution would be to have the service save the result in preference file/database and set a global variable to the time it saved it. The activity has a listener to the preference file/database. Before registering the listener, it checks the global variable to see if the result was put during the screen rotation (global var < currentTimeMillies()) and if true, gets the result, if not, registers the listener. Since the result might be put between the check and the registration, this has to be done inside a block in which the activity holds a lock that the service must acquire to put the result. This would also work, but it is way too complicated.
Is there a simpler and more elegant way of doing it, surviving a screen rotation?
回答1:
Have a look at my answer to this question:
How to handle IPC between a service and an activity (and its subactivity)?
Perhaps that will give you an idea.
EDIT (Add following suggestion):
Another approach would be to use a Receiver which you create in the Activity. On a screen rotation, the OS will call onRetainNonConfigurationInstance() where you can return the Receiver instance and it will get handed off to the new Activity (see getLastNonConfigurationInstance()). NOTE: These methods have been deprecated in 4.0 and you can use a Fragment and setRetainInstance() to achieve similar behaviour.
来源：https://stackoverflow.com/questions/10664114/send-data-from-service-to-activity-and-screen-rotation