Handling files on iOS devices

File management APIs on iOS devices

App sandbox files versus external files (openFile)

For an app running on an iOS device, filenames returned by front calls such as standard.openFile are of two types:

1. The filename does not start with "file:" prefix: It is a file from the app sandbox, that can be processed with normal os.Path methods.
2. The filename starts with the "file:" prefix: It is an external file from other apps or an iCloud link: The file content should be copied ASAP into the sandbox via fgl_getfile().

To distinguish app sandbox files from external files, write a utiliy function:

FUNCTION mobile_file_type(filename STRING) RETURNS CHAR(1)
    CASE
        WHEN filename.getIndexOf("file:",1)==1
            RETURN "E" -- External file
        WHEN os.Path.exists(filename)
            RETURN "S" -- Sandbox file
        OTHERWISE
            RETURN "U" -- Undefined
    END CASE
END FUNCTION

Using external filenames (with file: prefix)

The filename returned by front calls such as standard.openFile or mobile.choosePhoto can be used in the standard.launchurl frontcall and (typically for images) in DISPLAY .. TO instructions, without the need to do a fgl_getfile() call.

In case the file content should be stored at the VM side for example in a database, an fgl_getfile() call is required. The file URL returned by openfile becomes obsolete after fgl_getfile(), because the resources belonging to that URL are freed by GMI when fgl_getfile() is done; Another fgl_getfile() call of the same URL will therefore not work.

Enable picking files from the apps sandbox (openFile)

By default, its not possible to pick files with standard.openFile from within the apps sandbox (and also not possible for the File app or another app to look inside the apps sandbox).

In order to be able to pick files from within the apps sandbox, one needs to enable the browsing in the deployed app by adding the following to a custom Info.plist file:

<key>UISupportsDocumentBrowser</key>
<true/>

Note that enabling this key also enables the Files app or other iOS apps to put or delete files in your apps sandbox.

Custom file extensions for openFile/openFiles

By default, common extensions such as *.pdf or *.png are recognized by the openFile/openFiles front calls.

User-defined extensions like *.err or *.myext will by default be grayed in the iOS file picker.

To enable picking files with user-defined extension, these must be declared in your custom Info.plist file.

Search the iOS development documentation about ""Info.plist custom UTI", to find how to setup your Info.plist file and make the app handle your specific file extensions.