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A small Android library to manage one-off operations for API 14 and higher.

Some things should happen once.

  • Users should only get the guided tour once.
  • Release notes should only pop up once every app upgrade.
  • Your app should only phone home to update content once every hour.

Once provides a simple API to track whether or not your app has already performed an action within a given scope.


First things first, you'll need to initialise Once on start up. In your Application class's onCreate() override add the follow:


Checking if something has been done

Now you're ready to go. Say you wanted to navigate to a 'WhatsNew' Activity every time your app is upgraded:

String showWhatsNew = "showWhatsNewTag";

if (!Once.beenDone(Once.THIS_APP_VERSION, showWhatsNew)) {
    startActivity(new Intent(this, WhatsNewActivity.class));

Or if you want your app tour to be shown only when a user install, simply check the tag using the THIS_APP_INSTALL scope:

if (!Once.beenDone(Once.THIS_APP_INSTALL, showAppTour)) {

Your app operations can also be rate-limited by time spans. So for example if you only want to phone back to your server a maximum of once per hour, you'd do the following:

if (!Once.beenDone(TimeUnit.HOURS, 1, phonedHome) { ... }

If checking by time bounds is not enough you can manually get the Date of last time a tag was marked done by:

Date lastDone = Once.lastDone(brushedTeeth);

This will return null if the tag has never been marked as done.

Marking something as to do

Say one part of your app triggers functionality elsewhere. For example you might have some advanced feature onboarding to show on the main activity, but you only want to show it once the user has seen the basic functionality.

// in the basic functionality activity
Once.toDo(Once.THIS_APP_INSTALL, "show feature onboarding");

// back in the home activity
if (Once.needToDo(showAppTour)) {
    // do some operations

    // after task has been done, mark it as done as normal

When a task is marked done it is removed from the set of tasks 'to do' so subsequent needToDo(tag) calls will return false. To stop the tag from being added back to your todo list each time the user looks at the basic functionality task, we've added a scope to the todo call: toDo(Once.THIS_APP_INSTALL, tag). You could also use the THIS_APP_VERSION scope for todo's which should happen once per app version, or leave off scope complete for tasks which should be repeated every time.

Doing something once per X events

Sometimes you need to keep track of how many times something has happened before you act on it. For example, you could prompt the user to rate your app after they've used the core functionality three times.

// Once again in the basic functionality activity
if (Once.beenDone("action", Amount.exactly(3))) {

You can also change the count checking from exactly(int x) times, to either Amount.lessThan(int x) times or Amount.moreThan(int x) times. When you don't specific a particular amount, Once will default to Amount.moreThan(0) i.e. checking if it's ever been done at all.

To de-noise your code a bit more you can also static-import the Once methods, so usage looks a bit cleaner

import static jonathanfinerty.once.Once.THIS_APP_INSTALL;
import static jonathanfinerty.once.Once.beenDone;
import static jonathanfinerty.once.Once.markDone;


if (!beenDone(THIS_APP_VERSION, tagName)) {


Add a library dependency to your app module's build.gradle:

dependencies {
    compile 'com.jonathanfinerty.once:once:1.2.2'

You'll need to have jcenter() in your list of repositories


Try out the sample app here: https://play.google.com/store/apps/details?id=jonathanfinerty.onceexample and have a look at it's source code in once-example/ for more simple usage.


Once was made in '20%' time at Huddle, where its used to help build our Android apps. Pete O'Grady and Paul Simmons also provided invaluable feedback.

Pull requests and github issues are more than welcome and you can get in touch with me directly @jonfinerty.


Copyright 2018 Jon Finerty

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at


Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
See the License for the specific language governing permissions and
limitations under the License.

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