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 errors.

My question is: How should I handle errors in LiveData, e.g. when it's backed by some network resource that can fail to be retrieved due to an IOException?

Answer 1

In one of Google's sample apps for Android Architecture Components they wrap the LiveData emitted object in a class that can contain a status, data, and message for the emitted object.

https://github.com/googlesamples/android-architecture-components/blob/master/GithubBrowserSample/app/src/main/java/com/android/example/github/vo/Resource.kt

With this approach you can use the status to determine if there was an error.

Answer 2

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

This is your Wrapper Model

public class StateData<T> {      @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<T> loading() {         this.status = DataStatus.LOADING;         this.data = null;         this.error = null;         return this;     }      public StateData<T> success(@NonNull T data) {         this.status = DataStatus.SUCCESS;         this.data = data;         this.error = null;         return this;     }      public StateData<T> error(@NonNull Throwable error) {         this.status = DataStatus.ERROR;         this.data = null;         this.error = error;         return this;     }      public StateData<T> 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<T> extends MutableLiveData<StateData<T>> {      /**      * Use this to put the Data on a LOADING Status      */     public void postLoading() {         postValue(new StateData<T>().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<T>().error(throwable));     }      /**      * Use this to put the Data on a SUCCESS DataStatus      * @param data      */     public void postSuccess(T data) {         postValue(new StateData<T>().success(data));     }      /**      * Use this to put the Data on a COMPLETE DataStatus      */     public void postComplete() {         postValue(new StateData<T>().complete());     }  } 

And this is how you use it

StateLiveData<List<Book>> 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<List<Book>> books) {       switch (books.getStatus()) {             case SUCCESS:                 List<Book> 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;         }     }