How to get value from LiveData synchronously?

问题

For LiveData, is there something similar to blockingNext or blockingSingle in RxJava's Observable to get the value synchronously? if not, how can i achieve the same behavior?

回答1:

You can call getValue() to return the current value, if there is one. However, there is no "block until there is a value" option. Mostly, that is because LiveData is meant to be consumed on the main application thread, where indefinitely-blocking calls are to be avoided.

If you need "block until there is a value", use RxJava and ensure that you are observing on a background thread.

回答2:

You can use Future to synchronize your data like this:

 LiveData<List<DataModel>> getAllDatasForMonth(final String monthTitle) {
    Future<LiveData<List<DataModel>>> future = DatabaseHelper.databaseExecutor
            .submit(new Callable<LiveData<List<DataModel>>>() {
        @Override

        public LiveData<List<DataModel>> call() throws Exception {
            mAllDatasForMonth = mDataDao.getDatasForMonth(monthTitle);
            return mAllDatasForMonth;
        }
    });
    try {
        //with get it will be wait for result. Also you can specify a time of waiting.
        future.get();
    } catch (ExecutionException ex){
        Log.e("ExecExep", ex.toString());
    } catch (InterruptedException ei) {
        Log.e("InterExec", ei.toString());
    }
    return mAllDatasForMonth;
}

来源：https://stackoverflow.com/questions/50069857/how-to-get-value-from-livedata-synchronously