future

Flutter: A few ways to simulate slow-responding functions and methods alvin September 21, 2019 - 2:57pm

As a quick note, here are a couple of examples of how to simulate a slow-responding Flutter method:

How to correctly create a Flutter FutureBuilder (for SharedPreferences, REST services, and database access)

At the time of this writing (September 19, 2019), there’s a lot of bad information in books and on the internet about how to use a Flutter FutureBuilder. That bad information caused me to waste a lot of time over the last two days. I don’t have time today to explain everything, but in short, here’s a technically correct FutureBuilder example:

A Dart Future/then/catchError example

When I was trying to debug a problem that I thought was related to Flutter’s SharedPreferences library, I ended up rewriting a preferences method to use code like this rather than the normal approach:

Future<SharedPreferences> fPrefs = SharedPreferences.getInstance();
fPrefs.then((value) {rez = value.getBool(KEY_ENABLE_NOTIFICATIONS) ?? false; })
   .catchError((e) {
       debugPrint("===== ERROR: ${e.error}");
       return 60;
   });
return rez;

While that ended up being a waste of time, the benefit of my side excursion is that I get to show this example of how to use then and catchError with a Dart future. So if you wanted to see a Dart Future/then/catchError example, I hope this is helpful.

How to use a Future with a Duration delay in Dart (and Flutter)

As a quick note, here are two examples of how to use a Future with a Duration delay in Dart (and Flutter):

// example 1
Future<bool> _getFutureBool() {
    return Future.delayed(Duration(milliseconds: 500))
        .then((onValue) => true);
}

// example 2
print('1');
Future.delayed(const Duration(milliseconds: 500), () {
    print('Hello, world');
});
print('2');

If you’re comfortable with Dart futures, you know that the second example will (eventually) print this output:

1
2
Hello, world

Never be a prisoner of your past

“Never be a prisoner of your past. It was a lesson, not a life sentence.”

~ possibly from Anna Grace Taylor

Humans as transitional beings alvin August 19, 2019 - 9:31am

“In a book I read recently, the author talked about humans as transitional beings — beings who are neither fully caught nor fully free, but are in the process of awakening. I find it helpful to think of myself this way. I’m in the process of becoming, in the process of evolving. I’m neither doomed nor completely free, but I’m creating my future with every word, every action, every thought.”

~ Pema Chödrön

Your future needs you. Your past doesn’t. alvin August 17, 2019 - 10:42am

“Your future needs you. Your past doesn’t.”

(I don’t know who originally created this image, but I like it. Kudos.)

Simple concurrency with Scala Futures (Futures tutorial)

Table of Contents1 - Problem2 - Solution3 - Run one task, but block4 - Run one thing, but don’t block, use callback5 - The onSuccess and onFailure callback methods6 - Creating a method to return a Future[T]7 - How to use multiple Futures in a for loop8 - Discussion9 - A future and ExecutionContext10 - Callback methods11 - For-comprehensions (combinators: map, flatMap, filter, foreach, recoverWith, fallbackTo, andThen)12 - See Also13 - The Scala Cookbook

This is an excerpt from the Scala Cookbook (partially modified for the internet). This is Recipe 13.9, “Simple concurrency with Scala Futures.”

Back to top

Problem

You want a simple way to run one or more tasks concurrently in a Scala application, including a way to handle their results when the tasks finish. For instance, you may want to make several web service calls in parallel, and then work with their results after they all return.

Back to top

Solution

A Future gives you a simple way to run an algorithm concurrently. A future starts running concurrently when you create it and returns a result at some point, well, in the future. In Scala, it’s said that a future returns “eventually.”