在片段中将数据放在额外的地方是错误的吗？

Question

I have one Activity and want to share data between that Activity and fragments. I put data in extra while in a fragment and put also other data in it. That way I Have a shared Bundle across my application. I only see examples of passing a Bundle to an Intent but its also possible to change that data while in another fragment. This does not break with the self-containment of fragments. I dont put them in some method in activity because then you will have to cast the activity. Can anybody tell me its right to do? I know about shared pref but I dont want a file based solution. I know about passing parameters with newInStance but I also need to save data back in fragments. passing parameters is only forward not shared.

Answer 1

Passing data from activity/fragment back & forth using Bundles would have some limitations and issues for instance:

• To pass a complex object, you'd need to use a serializable marked with a key.

• Keeping shared keys in different parts can lead to runtime errors or data loss if keys are wrong.

• Serialized objects are not recommended, but it can be solved with Parcelables. But maintaining that is not that easy for complex objects check here , and you would need to customize that for different types of objects.

• Still you don't share data among different fragments but they're just transported; and need to be transported over and over again when you go to a new part of your app.

• Not guaranteed to keep the data if the activity is recreated.

Instead of that you'd use ViewModels through MVVM structure where:

• Data can be shared on different levels of lifecycle scopes; this means that if the ViewModel is instantiated through ViewModelProvider in activity; then it can be accessed in any part of the activity, or underlying fragments. And if you want to keep only data shared between any fragment and its underlying fragments; you'd bound the ViewModel instantiation to that fragment instead.

• ViewModel is instantiated once in the owner, and accessed in the subordinate fragments with no re-instantiation.

• If the activity is re-created, it receives the same ViewModel instance that was created by the owner, and the view's data won't be lost.

• When the owner activity/fragment is finished, the framework automatically calls the ViewModel's onCleared() method so that it can clean up the resources.

Here is a code lab that you'd check.