如何在 Android 中的多个活动和片段中保留对象？

Question

I created a class "Car" and I have a list of instantiated Cars created in my MainActivity. I have a master/detail flow with an ItemListActivity as well, which should be able to receive a specific car from MainActivity.

This master/detail flow works as a Settings Menu, where there are multiple fragments acting as different types of settings (Build, engine, etc.)

The master/detail flow needs to then get all the changes made to the edit text, and update the fields of the Car that it received, and than send it back to MainActivity.

I'm not sure if this is 1) possible or 2) the best way to approach this problem. Should I be keeping the list of objects in MainActivity? Is there a better way to keep an object that will be used globally?

Answer 1

I would recommend having a ViewModel in your activity and get the ViewModel instance from your fragments as follows.

carViewModel = ViewModelProviders.of(getActivity()).get(CarViewModel.class);

The CarViewModel might have the necessary elements to build a car and from each fragments, you can just update that ViewModel that resides in your activity.

The CarViewModel might have a function call buildCar that you can trigger when you are done building your car from different fragments. The ViewModel will be bound to the lifecycle of the activity and hence if you close the activity, the information will be lost.