Question

Basically I want to know if apps work and store data independent of one another or if there is a possibility for one app to modify another. Also…

In what folder are apps and their data saved on a phone?

If I modify data locally in an app, will the data be saved in a public place where other apps have access or is it saved to a folder specific to that app?

Answer 1

iOS is kinda not that mature in inter-app communication.

Data can be shared between apps using the system clipboard and transmitted over the network through mediums such as email and webservices.

iOS devices also provide a straightforward and well defined method for apps to send messages and data via URLs and filetype handlers. These techniques diverge into two categories:

1. Custom URL prefixes, e.g. someapp://something/somethingelse?somestuff=whatever
2. Custom file type handlers by file extension (e.g. *.txt) or by MIME type (e.g. text/plain).

Custom URL prefixes are useful for when two apps have established a specific protocol, while custom file type handlers are much more general, and are designed in a way that allows any app to register itself and participate. This article describes the latter: custom file type handlers for chemical data. If you register your app for a certain filetype it will look like so –

Reg. your second part of question – If I modify data locally in an app, will the data be saved in a public place where other apps have access or is it saved to a folder specific to that app?

As such, each application is restricted in terms of where it can store data on the file system of the device. iOS achieves this by allowing applications to read and write only to their own Documents and tmp directories. Within these two directories the corresponding application can create files and also sub-directories to any required level of depth. This area constitutes the application’s sandbox and the application cannot create or modify files or directories outside of these directories. Check this