Is it possible to make access to the file / directory from Objective-C?

Dropbox does offer an API you can use for listing, uploading, and downloading files, among other operations, in connected accounts. You can find everything you need to get started with the Dropbox API, including documentation, tutorials, and SDKs here:

https://www.dropbox.com/developers

For Objective-C in particular, we recommend using the Objective-C SDK:

https://github.com/dropbox/dropbox-sdk-obj-c

There are instructions there for getting started with the SDK, as well as a number of basic examples of operations such as creating and listing folders, and uploading and downloading files.

Thank. Unfortunately, I did not find the information I was interested in in the documentation and in the examples. First of all, I am interested in the issue of data access. I do not want to give public access to user data. I want to give reading access to a certain circle of persons / people so that they can access this data.

To clarify, do you want to enable these specific people to access data from your own Dropbox account in particular, or do you want them to each access their own Dropbox account?

The API was designed with the intention that each user would link their own Dropbox account, in order to interact with their own files. However, it is technically possible to connect to just one account. The SDKs don't offer explicit support for it and we don't recommend doing so though, for various technical and security reasons.

No, I want to make a mobile application so that users can store their data (for example, photos) in Dropbox, but also have the opportunity to give a certain circle of people access to this data. For example, the user Adam gives access to see the photo to the user Bob. Each participant will have to register their own account.

Thanks for clarifying! That use case is certainly possible, and is what the API is designed for.

When you set up the SDK as documented, each user can connect their own account. Their files are private by default, but they can choose to share files with other members of their choice, if desired.

They can do so via the Dropbox product itself, or via the API if the app implements it. For instance, an app can use the shareFolder and addFolderMember methods to share and invite members to a folder. (Note that for using shared folders like this, you'll need to register an app for the "full Dropbox" permission, if you haven't already.)

Thanks. This is what I was looking for! 

There was another question. Can I use the SDK to get a list of files/folders to which I was invited?

Yes, there are a number of methods you may be interested in, depending on the exact type of sharing you're referring to:

• listFolders/listFoldersContinue: to list all of the "shared folders" the user has access to (e.g., from addFolderMember from another user).
• listMountableFolders/listMountableFoldersContinue: to list the "shared folders" the user has access to (e.g., from addFolderMember from another user) but doesn't have "mounted". (Use mountFolder to mount any of them.)
• listReceivedFiles/listReceivedFilesContinue: to list the files the user has been sent directly.