Save file to public directory using Cordova FileTransfer

Question

I need to download files on my mobile device and make them accessible for other apps (using Android and iOS).

I managed to download a file to the SD card (cordova.file.externalDataDirectory), but this only exists on Android and even then I cannot rely on every device having an SD card.

When I download to the device storage (cordova.file.dataDirectory), the file is private to my app and therefore not accessible for other apps. The file can be opened in the InAppBrowser, but I would prefer to use the respective default app.

Is there a way to get a path to a directory publicly available on all devices?

The paths returned by the solution suggested in https://stackoverflow.com/a/21375812/3432305 are both private on Android...

EDIT:

I think I should describe my use case so it's clearer what I'm trying to achieve: I want to open files from my in app chat using the respective default app (pdf viewer, image viewer etc.). Because the Cordova File Opener plugin only accepts files from the local file system, I need to save them first. But they don't necessarily need to be accessible from outside my app afterwards...

Answer 1

On Android, external storage directories always exist; if the device doesn't have a physical SD card, Android will emulate it. see getExternalStorageDirectory :

Note: don't be confused by the word "external" here. This directory can better be thought as media/shared storage. It is a filesystem that can hold a relatively large amount of data and that is shared across all applications (does not enforce permissions). Traditionally this is an SD card, but it may also be implemented as built-in storage in a device that is distinct from the protected internal storage and can be mounted as a filesystem on a computer.

Therefore cordova.file.externalDataDirectory will always resolve. However, for sharing data between apps, you probably want to use cordova.file.externalRootDirectory - External storage (SD card) root. See cordova-plugin-file.

This way you can store files in a place that's easier to access from another app e.g. /sdcard/my_shared_data/

On iOS, it's more difficult to share files because apps are intentionally isolated from each other due to security policy, as Apple's Inter-App Communication Guide says:

Apps communicate only indirectly with other apps on a device

You best bet on iOS is to share the data by synching it via iCloud. See the section Configuring a Common Ubiquity Container for Multiple Apps in iCloud Design Guide, which says:

... perhaps you provide two apps that interoperate and need access to each other’s files. In both of these examples, you obtain the needed access by specifying a common ubiquity container and then requesting access to it from each app.