How do you save a ViewModel state?

How do you save a ViewModel state?

SavedStateProvider is an interface that defines a single saveState() method that returns a Bundle containing the state you want to save. When SavedStateHandle is ready to save its state, it calls saveState() to retrieve the Bundle from the SavedStateProvider and saves the Bundle for the associated key.

What should be done in order to preserve the state of an activity?

Saving UI States

1. Table of contents.
2. User expectations and system behavior.
3. Options for preserving UI state.
4. Use ViewModel to handle configuration changes.
5. Use onSaveInstanceState() as backup to handle system-initiated process death.
6. Use local persistence to handle process death for complex or large data.

How do you save a fragment state?

Various Android system operations can affect the state of your fragment. To ensure the user’s state is saved, the Android framework automatically saves and restores the fragments and the back stack. Therefore, you need to ensure that any data in your fragment is saved and restored as well.

What is saved state handle?

androidx.lifecycle.SavedStateHandle. A handle to saved state passed down to ViewModel . You should use SavedStateViewModelFactory if you want to receive this object in ViewModel ‘s constructor. This is a key-value map that will let you write and retrieve objects to and from the saved state.

How does ViewModel survive change configuration?

Handle configuration changes: ViewModel objects are automatically retained whenever activity is recreated due to configuration changes. Lifecycle Awareness: ViewModel objects are also lifecycle-aware. They are automatically cleared when the Lifecycle they are observing gets permanently destroyed.

What allows you to properly restore a user state when an activity is restarted?

onSaveInstanceState() is called by Android if the Activity is being stopped and may be killed before it is resumed! This means it should store any state necessary to re-initialize to the same condition when the Activity is restarted.

How do you pass intent?

The easiest way to do this would be to pass the session id to the signout activity in the Intent you’re using to start the activity: Intent intent = new Intent(getBaseContext(), SignoutActivity. class); intent. putExtra(“EXTRA_SESSION_ID”, sessionId); startActivity(intent);

What is a fragment state?

The concept of State comes from OOP, not from android, to simplify: an object has a state (the data) and a behavior (the code). Fragments and Activities work a bit different, fragments will retain the state if they are stopped, but they will lose it of the activity that manages them is destroyed (unless you retain it).

How do you load a fragment once and save its state?

1 Answer

1. use one of the lifecycle methods to put the code for retrieving the data(so, don’t use setUserVisibleHint() ), like onActivityCreated()
2. there, you will need to use the above methods to first see if the data isn’t already available(if the fragment was previously loaded and the data was saved).

How does ViewModel survive screen rotation?

Android ViewModel recreated on screen rotation

1. Activity is started and ViewModel instance is created.
2. Activity is put to background.
3. Device screen is rotated.
4. Activity is put back to foreground.
5. ViewModel’s onCleared method is called and new object is created.

How do you bind ViewModel to activity?

1. First, have your ViewModel expose a LiveData object, and you can start the LiveData with an empty value.
2. Second, have your view (activity/fragment) observe that LiveData and change UI accordingly.
3. Third, as a result of data becoming available you need to update your LiveData object.

How do I get ViewModel in activity?

Simple ViewModel

1. Add dependencies in your app-level build. gradle .
2. Separate out all your data from your activity by creating a class that extends the ViewModel .
3. Create a ViewModel instance in your activity to use it.
4. Set up communications between your ViewModel and your View layer.

How does the saved state module in ViewModel work?

When using this module, ViewModel objects receive a SavedStateHandle object through its constructor. This object is a key-value map that lets you write and retrieve objects to and from the saved state.

Can a savedstatehandle restore only the current ViewModel?

Don’t forget that SavedStateHandle restores only the state of the current ViewModel. If your app is dependent on in-memory Singletons ( object in Kotlin) then you would need to take care of the restoration of those objects state yourself.

What’s the difference between ViewModel and onsaveinstancestate?

Generally speaking, you’ll probably use both ViewModel and onSaveInstanceState (). Users take various actions as they run an app. For almost every explicit action, users expect feedback or an output. Think of output in terms of app state. The expectation could be to either clear or preserve it.

Can you inject activity into savedstate ViewModel?

We cannot just inject whatever Activity/Fragment instance here. Unfortunately, the traditional approach is no longer valid when using SavedState ViewModel. As mentioned previously, you have to create one Factory per ViewModel while making sure that you pass the right SavedStateRegistryOwner instance.