NativeScript Downloader

@voicethread/nativescript-downloader

This downloader plugin exports class Downloader that has a single function download().

For iOS, Downloader uses NSURLSession to initiate a download from a valid URL.

For Android, Downloader uses DownloadManager to initiate a download from a valid URL.

https://github.com/VoiceThread/nativescript-plugins/assets/20136906/80d40e3f-2c42-4d61-8213-52b84e965ac9

Contents

• NativeScript Downloader android
  • Contents
  • Installation
  • Usage
  • Supported Downloader Options
    • Android Specifics
    • iOS Specifics
  • Acknowledgements
  • License

Installation

npm install @voicethread/nativescript-downloader

Usage

The best way to understand how to use the plugin is to study the demo app included in this repo. You can see plugin being used in a TypeScript application by looking at apps/demo/src/plugin-demos/downloader.ts.

1. Import the plugin.

import { DownloadDestination, Downloader, DownloadOptions, MessageData } from '@voicethread/nativescript-downloader';

2. Create a downloader instance.

const dp = new Downloader();

3. The only required option is the URL to be downloaded. You can also pass other options as listed in DownloadOptions before starting the download. You can listen to events emitted by the download during operation in case you want to update a download status message/indicator or handle an error. Upon success, the plugin will return a File reference to the downloaded file located in the app cache directory for Android and the app document's directory for iOS, which can then be used directly by the dev without extra permissions for any other operations on the file.

dp.on(Downloader.DOWNLOAD_STARTED, (payload: MessageData) => {
  console.log('started', payload?.data?.contentLength);
});
dp.on(Downloader.DOWNLOAD_PROGRESS, (payload: MessageData) => {
  console.log(' >>>>>  ', payload?.data?.progress, payload?.data?.url, payload?.data?.destinationFilename);
});
dp.on(Downloader.DOWNLOAD_COMPLETE, (payload: MessageData) => {
  console.log('finished', payload?.data?.filepath);
});
dp.on(Downloader.DOWNLOAD_ERROR, (payload: MessageData) => {
  console.log('ERROR!', payload?.data);
});
dp.download({ url: 'https://some.domain.com/file.txt' }).then((file: File) => {
  if (!file) {
    return console.error('Failed to download file!');
  }
  console.log('Finished downloading file ', file.path);
});

Supported Downloader Options

interface DownloadOptions {
  url: string; //must be a valid url, usually https unless you allow http in your app
  request?: RequestOptions; //request header strings to be passed to the https connection
  destinationPath?: string; //must be a valid path for app to create a new file (existing directory with valid filename)
  destinationFilename?: string; //must be a string like XXXX[].[YYYYYY] without any path preceding
  destinationSpecial?: DownloadDestination; //Special destination options discussed below
  notification?: boolean; //Android-only. Show system notification for download success/failure. defaults to false
}

const enum DownloadDestination {
  picker = 'show-picker', //present user with UI to choose destination directory to save a copy
  gallery = 'photos-gallery', //iOS only, saves a copy of image/video files (matched by file extension) to iOS Photos Gallery, requires user permission.
  downloads = 'downloads-directory', //Android only, uses MediaStore or legacy approach to save a copy in Android Download directory
}

For both platforms, the plugin will attempt to download the file with the filename/path supplied by the user in options, or try to find a filename to use from the url. In either case, if a file already exists at any of the output paths where a copy is being saved, it will instead append a '-#' to the filename before saving to ensure there is no conflict.

Android Specifics

Android apps will download files by default to the app's cache directory, which is the only directory supported by DownloadManager and no special permissions are necessary. This will correspond to android.content.Context.getExternalCacheDir() if the device has an sd card, or android.content.Context.getCacheDir() if not. This file can then be used directly for other purposes in the app without any additional permissions/requests.

By default, the plugin disabled Android system notifications of downloads, which also requires you to add that permission to the Android Manifest like so:

<manifest ... >
  <uses-permission android:name="android.permission.DOWNLOAD_WITHOUT_NOTIFICATION"/>

You can choose to enable these notifications which will show the user progress and completion/failure notifications.

Android version of plugin supports two special destination approaches. First, destinationSpecial: DownloadDestination.picker will first download the file to the default cache directory, and then present the user with a picker UI so that they select where they'd like a copy saved. This approach avoids permission requirements since the user is involved in the destination choice. Second, destinationSpecial: DownloadDestination.downloads will save a copy to the device's Download directory in case the user wants to use that file in another application from an easy to find location. API versions > 28 use MediaStore, and no extra permissions are necessary. For API versions 28 and below, you'll need to ensure you have Android Manifest permissions defined using:

<manifest ... >
  <uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE"/>
  <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>

iOS Specifics

iOS applications will download files by default to the application's documents directory, which is defined in Nativescript as knownFolders.documents() and does not require any extra permissions from the user. This also has the advantage of being the location where an application can make downloaded files visible to other apps once it has been configured as a document provider.

The iOS version of the plugin supports two special destination approaches. First, destinationSpecial: DownloadDestination.picker will first download the file to the application documents directory, and then present the user with a picker UI so that they can select where they'd like a copy saved. This approach avoids permission requirements since the user is involved in the destination choice. Note: This is only available on iOS 13+

Second, destinationSpecial: DownloadDestination.gallery will save a copy to the device's Photos Gallery in case the user wants to use that file in another application from an easy to find location. This approach requires the user to grant photo library permission first in order to save the downloaded file. Your app might be rejected from the Apple App Store if you do not provide a description about why you need this permission. The default message "Requires access to photo library." might not be enough for the App Store reviewers. You can customize it by editing the app/App_Resources/iOS/Info.plist file in your app and adding something like the following:

<key>NSPhotoLibraryUsageDescription</key>
<string>Requires access to save downloaded media to photo library.</string>

NOTE: if you do use the perms plugin in a production app, make sure to read their README.md first, as using this plugin in production apps will require you to add all iOS Info.plist permission strings to avoid being rejected by automatic processing since the plugin includes code for all permission types.

Acknowledgements

This plugin was inspired by https://github.com/tobydeh/nativescript-download-progress/.

License

Apache License Version 2.0