nativescript-background-fetch ·

By Transistor Software, creators of NativeScript Background Geolocation

---

Background Fetch is a very simple plugin which will awaken an app in the background about every 15 minutes, providing a short period of background running-time. This plugin will execute your provided callbackFn whenever a background-fetch event occurs.

There is no way to increase the rate which a fetch-event occurs and this plugin sets the rate to the most frequent possible — you will never receive an event faster than 15 minutes. The operating-system will automatically throttle the rate the background-fetch events occur based upon usage patterns. Eg: if user hasn't turned on their phone for a long period of time, fetch events will occur less frequently.

The Android plugin provides a "Headless"]() implementation allowing you to continue handling events with Javascript even after app-termination (see @config enableHeadless)

Installing the plugin

   $ tns plugin add nativescript-background-fetch

Setup

BackgroundFetch requires implementation of the AppDelegate method applicationPerformFetchWithCompletionHandler. In your app.ts, add the following block (If you've already implemented an AppDelegate, simply add the method applicationPerformFetchWithCompletionHandler to your existing implementation).

app.ts

import * as app from 'application';

+import {BackgroundFetch} from "nativescript-background-fetch";

+if (app.ios) {
+  class MyDelegate extends UIResponder implements UIApplicationDelegate {
+    public static ObjCProtocols = [UIApplicationDelegate];

+    public applicationPerformFetchWithCompletionHandler(application: UIApplication, completionHandler:any) {
+      BackgroundFetch.performFetchWithCompletionHandler(completionHandler, application.applicationState);
+    }
+  }
+  app.ios.delegate = MyDelegate;
+}

app.start({ moduleName: 'main-page' });

NOTE If your build fails with the following errors:

app/app.ts(6,28): error TS2304: Cannot find name 'UIResponder'.
app/app.ts(6,51): error TS2304: Cannot find name 'UIApplicationDelegate'.
app/app.ts(7,36): error TS2304: Cannot find name 'UIApplicationDelegate'.

Add the following items to references.d.ts in the root of your project (create it if it doesn't exist):

📂 /references.d.ts

/// <reference path="./node_modules/tns-platform-declarations/ios.d.ts" />
/// <reference path="./node_modules/tns-platform-declarations/android.d.ts" />

Config

Common Options

@param {Integer} minimumFetchInterval [15]

The minimum interval in minutes to execute background fetch events. Defaults to 15 minutes. Note: Background-fetch events will never occur at a frequency higher than every 15 minutes. Apple uses a secret algorithm to adjust the frequency of fetch events, presumably based upon usage patterns of the app. Fetch events can occur less often than your configured minimumFetchInterval.

Android Options

@config {Boolean} stopOnTerminate [true]

Set false to continue background-fetch events after user terminates the app. Default to true.

@config {Boolean} startOnBoot [false]

Set true to initiate background-fetch events when the device is rebooted. Defaults to false.

❗ NOTE: startOnBoot requires stopOnTerminate: false.

@config {Boolean} forceReload [false]

Set true to automatically relaunch the application (if it was terminated) — the application will launch to the foreground then immediately minimize. Defaults to false.

@config {Boolean} enableHeadless [false]

Set true to enable the Android "Headless Javascript" mechanism, for handling fetch events after app termination with a Javascript callback.

• 📂 app.ts

import * as application from 'application';

import {BackgroundFetch} from "nativescript-background-fetch";

if (application.android) {
  // This headless task will execute only when Android app is terminated.
  BackgroundFetch.registerHeadlessTask(async () => {
    console.log('[My BackgroundFetch HeadlessTask] onFetch');    
    // Do some asynchronous work (eg: HTTP Request)
    let result = await doWork();
    // Politely signal to the OS that our processing is complete.
    BackgroundFetch.finish();
  });

  // Your example task.
  let doWork = () => {
    return new Promise((resolve, reject) => {
      // Do some work.
      let result = true;  // <-- example result from HTTP request.
      if (true) { 
        resolve('OK') 
      } else {
        reject('OOPS!');
      }
    });
  }
}

application.run({ moduleName: 'app-root' });

Methods

Method Name	Arguments	Notes
performFetchWithCompletionHandler	Function	This method is required to be called in your custom AppDelegate, initiated the background-fetch event received from iOS. See Setup instructions above.
configure	{config}, callbackFn, failureFn	Configures the plugin's fetch callbackFn. This callback will fire each time an iOS background-fetch event occurs (typically every 15 min). The failureFn will be called if the device doesn't support background-fetch.
status	callbackFn	Your callback will be executed with the current status (Integer) 0: Restricted, 1: Denied, 2: Available. These constants are defined as BackgroundFetch.STATUS_RESTRICTED, BackgroundFetch.STATUS_DENIED, BackgroundFetch.STATUS_AVAILABLE (NOTE: Android will always return STATUS_AVAILABLE)
finish	fetchResult	Valid values for fetchResult (Integer) include BackgroundFetch.FETCH_RESULT_NEW_DATA (0), BackgroundFetch.FETCH_RESULT_NO_DATA (1), and BackgroundFetch.FETCH_RESULT_FAILED (2). You MUST call this method in your fetch callbackFn provided to #configure in order to signal to iOS that your fetch action is complete. iOS provides only 30s of background-time for a fetch-event -- if you exceed this 30s, iOS will kill your app.
start	successFn, failureFn	Start the background-fetch API. Your callbackFn provided to #configure will be executed each time a background-fetch event occurs. NOTE the #configure method automatically calls #start. You do not have to call this method after you #configure the plugin
stop	successFn, failureFn	Stop the background-fetch API from firing fetch events. Your callbackFn provided to #configure will no longer be executed.
registerHeadlessTask	callback	Registers an Android "Headless Task" to receive Android background-fetch events when your application is terminated. (:warning: requires stopOnTerminate: false and enableHeadless: true)

Example

A full example could be:

import {BackgroundFetch} from "nativescript-background-fetch";

export class HelloWorldModel
  constructor() {
    super();

    // You can query the UIBackgroundRefreshStatus.  User can disable fetch.
    BackgroundFetch.status((status) => {
      console.log('- BackgroundFetch status: ', status);
    });

    // Configure Background Fetch
    BackgroundFetch.configure({
      stopOnTerminate: false,
      minimumFetchInterval: 30,  // minutes
      stopOnTerminate: false,    // Android-only
      startOnBoot: true          // Android-only
    }, () => {
      console.log("[js] BackgroundFetch event received");
      //
      // Do stuff.  You have 30s of background-time.
      //
      // When your job is complete, you must signal completion or iOS can kill your app.  Signal the nature of the fetch-event, whether you recevied:
      // FETCH_RESULT_NEW_DATA: Received new data from your server
      // FETCH_RESULT_NO_DATA:  No new data received from your server
      // FETCH_RESULT_FAILED:  Failed to receive new data.
      BackgroundFetch.finish(BackgroundFetch.FETCH_RESULT_NEW_DATA);
    }, (status) => {
      console.log('BackgroundFetch not supported by your OS', status);
    });

    // Later, to stop background-fetch events from firing:
    //BackgroundFetch.stop();

    // Or restart them again:
    /*
    BackgroundFetch.start(() => {
      console.log("BackgroundFetch successfully started");
    }, (status) {
      console.log("BackgroundFetch failed to start: ", status);
    });
    */
  }
}

Debugging

iOS

• Simulate background fetch events in XCode using Debug->Simulate Background Fetch
• iOS can take some hours or even days to start a consistently scheduling background-fetch events since iOS schedules fetch events based upon the user's patterns of activity. If Simulate Background Fetch works, your can be sure that everything is working fine. You just need to wait.

Android

• Observe plugin logs in $ adb logcat:

$ adb logcat *:S JS:V TSBackgroundFetch:V

• Simulate a background-fetch event on a device (insert <your.application.id>) (only works for sdk 21+:

$ adb shell cmd jobscheduler run -f <your.application.id> 999

• For devices with sdk <21, simulate a "Headless JS" event with (insert <your.application.id>)

$ adb shell am broadcast -a <your.application.id>.event.BACKGROUND_FETCH

Implementation

iOS

Implements performFetchWithCompletionHandler, firing a custom event subscribed-to in cordova plugin.

Android

Android implements background fetch using two different mechanisms, depending on the Android SDK version. Where the SDK version is >= LOLLIPOP, the new JobScheduler API is used. Otherwise, the old AlarmManager will be used.

Unlike iOS, the Android implementation can continue to operate after application terminate (stopOnTerminate: false) or device reboot (startOnBoot: true).

Licence

The MIT License

Copyright (c) 2013 Chris Scott, Transistor Software [email protected] http://transistorsoft.com

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.