How to handle error states with LiveData?

Question

The new LiveData can be used as a replacement for RxJava\'s observables in some scenarios. However, unlike Observable, LiveData has no callback for

Answer 1

You can extend from MutableLiveData and create a holder Model to wrap your data.

This is your Wrapper Model

public class StateData {

    @NonNull
    private DataStatus status;

    @Nullable
    private T data;

    @Nullable
    private Throwable error;

    public StateData() {
        this.status = DataStatus.CREATED;
        this.data = null;
        this.error = null;
    }

    public StateData loading() {
        this.status = DataStatus.LOADING;
        this.data = null;
        this.error = null;
        return this;
    }

    public StateData success(@NonNull T data) {
        this.status = DataStatus.SUCCESS;
        this.data = data;
        this.error = null;
        return this;
    }

    public StateData error(@NonNull Throwable error) {
        this.status = DataStatus.ERROR;
        this.data = null;
        this.error = error;
        return this;
    }

    public StateData complete() {
        this.status = DataStatus.COMPLETE;
        return this;
    }

    @NonNull
    public DataStatus getStatus() {
        return status;
    }

    @Nullable
    public T getData() {
        return data;
    }

    @Nullable
    public Throwable getError() {
        return error;
    }

    public enum DataStatus {
        CREATED,
        SUCCESS,
        ERROR,
        LOADING,
        COMPLETE
    }
}

This is your extended LiveData Object

public class StateLiveData extends MutableLiveData> {

    /**
     * Use this to put the Data on a LOADING Status
     */
    public void postLoading() {
        postValue(new StateData().loading());
    }

    /**
     * Use this to put the Data on a ERROR DataStatus
     * @param throwable the error to be handled
     */
    public void postError(Throwable throwable) {
        postValue(new StateData().error(throwable));
    }

    /**
     * Use this to put the Data on a SUCCESS DataStatus
     * @param data
     */
    public void postSuccess(T data) {
        postValue(new StateData().success(data));
    }

    /**
     * Use this to put the Data on a COMPLETE DataStatus
     */
    public void postComplete() {
        postValue(new StateData().complete());
    }

}

And this is how you use it

StateLiveData> bookListLiveData;
bookListLiveData.postLoading();
bookListLiveData.postSuccess(books);
bookListLiveData.postError(e);

And how it can be observed:

private void observeBooks() {
        viewModel.getBookList().observe(this, this::handleBooks);
    }

    private void handleBooks(@NonNull StateData> books) {
      switch (stepIds.getStatus()) {
            case SUCCESS:
                List bookList = books.getData();
                //TODO: Do something with your book data
                break;
            case ERROR:
                Throwable e = books.getError();
                //TODO: Do something with your error
                break;
            case LOADING:
                //TODO: Do Loading stuff
                break;
            case COMPLETE:
                //TODO: Do complete stuff if necessary
                break;
        }
    }