How to use Saved State module for ViewModel in Background Thread

Question

How to use Saved State module for ViewModel in Background Thread

For MutableLiveData we have the option to use setvalue and postvalue , where Postvalue can be used in background thread.

How ever How can we use BACKGROUND THREAD FOR Saved State module for ViewModel

here Is the code I am trying

public class CommonViewModel extends ViewModel {
    private SavedStateHandle mState;

    public CommonViewModel(SavedStateHandle savedStateHandle) {
        mState = savedStateHandle;
    }

    private static final String NAME_KEY = "name";
    private Executor mExecutor = Executors.newSingleThreadExecutor();

    public LiveData<ArrayList<CommonOwn>> getCart() {
        if (mState.getLiveData(NAME_KEY) == null) {
            initCart();
        }
        return mState.getLiveData(NAME_KEY);
    }

    public void initCart() {
        mState.set(NAME_KEY, new ArrayList<CommonOwn>());
    }

  public void addItemToCart(CommonOwn commonOwn) {
        if (getCart().getValue() == null) {
            initCart();
        }
        ArrayList<CommonOwn> cartItemList = new ArrayList<CommonOwn>(getCart().getValue());
        if (cartItemList.contains(commonOwn)) {
            int a = cartItemList.indexOf(commonOwn);
            cartItemList.remove(a);
        } else {
            cartItemList.add(commonOwn);
        }
       // mState.set(NAME_KEY, cartItemList);
        mExecutor.execute(new Runnable() {
            @Override
            public void run() {
                mState.set(NAME_KEY, cartItemList);

            }
        });
    }
}

when using background thread The following error occurs

java.lang.IllegalStateException: Cannot invoke setValue on a background thread
        at androidx.lifecycle.LiveData.assertMainThread(LiveData.java:487)
        at androidx.lifecycle.LiveData.setValue(LiveData.java:306)
        at androidx.lifecycle.MutableLiveData.setValue(MutableLiveData.java:50)
        at androidx.lifecycle.SavedStateHandle$SavingStateLiveData.setValue(SavedStateHandle.java:367)
        at androidx.lifecycle.SavedStateHandle.set(SavedStateHandle.java:256)
        at com.example.CommonViewModel$1.run(CommonViewModel.java:63)
        at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1113)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:588)
        at java.lang.Thread.run(Thread.java:818)

how can we solve this issue.

Answer 1

The following line can never be null:

mState.getLiveData(NAME_KEY) == null

Hope this illustrates the solution. You just rely on the MutableLiveData from SavedStateHandle:

public class CommonViewModel extends ViewModel {
    private MutableLiveData<ArrayList<CommonOwn>> cart;

    public CommonViewModel(SavedStateHandle savedStateHandle) {
        cart = savedStateHandle.getLiveData(NAME_KEY);
    }

    private static final String NAME_KEY = "name";
    private Executor mExecutor = Executors.newSingleThreadExecutor();

    public MutableLiveData<ArrayList<CommonOwn>> getCart() {
        return cart;
    }

    public void addItemToCart(CommonOwn commonOwn) {
        ArrayList<CommonOwn> cartItemList;
        if(cart.getValue() == null) {
            cartItemList = new ArrayList<CommonOwn>();
        } else {
            cartItemList = cart.getValue();
        }
        if (cartItemList.contains(commonOwn)) {
            int a = cartItemList.indexOf(commonOwn);
            cartItemList.remove(a);
        } else {
            cartItemList.add(commonOwn);
        }
        // mState.set(NAME_KEY, cartItemList);
        mExecutor.execute(new Runnable() {
            @Override
            public void run() {
                cart.postValue(cartItemList);
            }
        });
    }
}