react-native-background-fetch · [![npm](https://img.shields.io/npm/dm/react-native-background-fetch.svg)]() [![npm](https://img.shields.io/npm/v/react-native-background-fetch.svg)]()
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[![](https://dl.dropboxusercontent.com/s/nm4s5ltlug63vv8/logo-150-print.png?dl=1)](https://www.transistorsoft.com)

By [**Transistor Software**](http://transistorsoft.com), creators of [**React Native Background Geolocation**](http://www.transistorsoft.com/shop/products/react-native-background-geolocation)

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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 [HeadlessJS](https://facebook.github.io/react-native/docs/headless-js-android.html) implementation allowing you to continue handling events even after app-termination (see **[`@config enableHeadless`](#config-boolean-enableheadless-false)**)

## Installing the plugin ##

```Bash
$ npm install react-native-background-fetch --save
```

## iOS Setup
- [`react-native link` Setup](docs/INSTALL-LINK-IOS.md)
- [Cocoapods Setup](docs/INSTALL-COCOAPODS-IOS.md)
- [Manual Setup](docs/INSTALL-MANUAL-IOS.md)

## Android Setup
- [`react-native link` Setup](docs/INSTALL-LINK-ANDROID.md)
- [Manual Setup](docs/INSTALL-MANUAL-ANDROID.md)

### :information_source: Solving Android Gradle Conflicts.

Once of the most common build-issues with Android apps are gradle conflicts between modules specifying different versions of:
- `compileSdkVersion`
- `buildToolsVersion`
- Google `play-services` / `firebase` version.
- Google support libraries (ie `appcompat-v4`, `appcompat-v7`)

For more information, see the Wiki [Solving Android Gradle Conflicts](../../wiki/Solving-Android-Gradle-Conflicts)

## 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`.

:exclamation: **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 React Native's [Headless JS](https://facebook.github.io/react-native/docs/headless-js-android.html) mechanism, for handling fetch events after app termination.

* :open_file_folder: **`index.js`**
```javascript
import BackgroundFetch from "react-native-background-fetch";

let MyHeadlessTask = async (event) => {
  console.log('- BackgroundFetch HeadlessTask start');
  // Important:  await asychronous tasks when using HeadlessJS.
  await doAction();
  // Required:  Signal to native code that your task is complete.
  // If you don't do this, your app could be terminated and/or assigned
  // battery-blame for consuming too much time in background.
  BackgroundFetch.finish();
  console.log('- BackgroundFetch HeadlessTask finished');
}

// Simulate a long-running task (eg: HTTP request)
function doAction() { 
  let timeout = 5000;
  return new Promise(resolve => {
    setTimeout(() => {
      console.log('*** TIMEOUT ***');
      resolve();
    }, timeout);
  });
}

// Register your BackgroundFetch HeadlessTask
AppRegistry.registerHeadlessTask('BackgroundFetch', () => MyHeadlessTask);
```


## Methods

| Method Name | Arguments | Notes
|---|---|---|
| `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` | *none* | 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. |

## Example ##

```javascript

import BackgroundFetch from "react-native-background-fetch";

export default class App extends Component {
  componentDidMount() {
    // Configure it.
    BackgroundFetch.configure({
      minimumFetchInterval: 15, // <-- minutes (15 is minimum allowed)
      stopOnTerminate: false,   // <-- Android-only,
      startOnBoot: true         // <-- Android-only
    }, () => {
      console.log("[js] Received background-fetch event");
      // Required: Signal completion of your task to native code
      // If you fail to do this, the OS can terminate your app
      // or assign battery-blame for consuming too much background-time
      BackgroundFetch.finish();
    }, (error) => {
      console.log("[js] RNBackgroundFetch failed to start");
    });

    // Optional: Query the authorization status.
    BackgroundFetch.status((status) => {
      switch(status) {
        case BackgroundFetch.STATUS_RESTRICTED:
          console.log("BackgroundFetch restricted");
          break;
        case BackgroundFetch.STATUS_DENIED:
          console.log("BackgroundFetch denied");
          break;
        case BackgroundFetch.STATUS_AVAILABLE:
          console.log("BackgroundFetch is enabled");
          break;
      }
    });
  }
};
```

## 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`:
```bash
$ adb logcat *:S ReactNative:V ReactNativeJS:V TSBackgroundFetch:V
```
- Simulate a background-fetch event on a device (insert *&lt;your.application.id&gt;*) (only works for sdk `21+`:
```bash
$ adb shell cmd jobscheduler run -f <your.application.id> 999
```
- For devices with sdk `<21`, simulate a "Headless JS" event with (insert *&lt;your.application.id&gt;*)
```bash
$ adb shell am broadcast -a <your.application.id>.event.BACKGROUND_FETCH

```

## Implementation

### iOS

Implements [performFetchWithCompletionHandler](https://developer.apple.com/library/ios/documentation/UIKit/Reference/UIApplicationDelegate_Protocol/Reference/Reference.html#//apple_ref/occ/intfm/UIApplicationDelegate/application: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`](https://developer.android.com/reference/android/app/job/JobScheduler.html) API is used.  Otherwise, the old [`AlarmManager`](https://developer.android.com/reference/android/app/AlarmManager.html) 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 <chris@transistorsoft.com>
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
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