Building a Chat App in Swift Using Multipeer Connectivity Framework

Updated on May 15th, 2015

⏱ Reading Time: 4 mins

When programming in iOS, there are certain aspects of the SDK that pull the developers’ attention and interest a lot more than others, and one of them is the Multipeer Connectivity framework. As you know, the MPC framework is not new in iOS 8, instead it was first-introduced in the seventh (7th) version of it, about a year and a half ago. In the past, I’d written a couple of tutorials about it, and to tell the truth, I was surprised from the interest that people seemed to have about it. Now, some months later, I return with a new post regarding it, as I believe that there are still things that need to be explained.

You may wonder why I bring to the surface a topic a bit old, and not something new included in iOS 8. Well, I’m doing that for three reasons:

  1. Many readers have approached me through e-mail messages, asking how to perform various tasks in multipeer connectivity that were not mentioned in the previous two tutorials. By answering to all those messages, I found out that there’s a need that I hadn’t noticed earlier; People want more information about it, which is hard to find sometimes.
  2. The implementation I presented in the last couple tutorials was based in the use of a default, pre-made view controller existing in the iOS SDK for inviting other peers and establishing a connection. I found out that people was asking for manual implementation, and that’s something we are about to see here.
  3. I think that it will be quite useful and educational to see how to implement MPC in Swift.
Multipeer Connectivity Framework in Swift

During the lifetime of the multipeer connectivity framework, it has been proved that the possibilities that it came to offer gave birth to new ideas to a great number of developers. Connecting devices using such a simple way seems so attractive, and that’s why programmers want to integrate it into their applications. However, if you haven’t used the MPC framework yet, I must warn you: Sometimes it’s not as reliable as you may expect, and that’s something I’ve seen personally in my projects, and also other developers have reported to me. MPC uses both Bluetooth and WiFi to connect nearby devices, but even though it sounds too good and promising, sometimes the connection either fails or is to slow, leading to communication errors. That’s important in cases you need to transfer vital data. I would advice you to use a backup communication solution (such as a web service), so you make sure that there is an alternative and your application will continue to work even if the MPC fails. However, despite to what I just said, I still believe that MPC if a good tool for all iOS developers, so it worths it one (last) more tutorial.

Getting into the details of MPC is not something I’m planning to do. If you want to get a taste of it, then simply pay a visit to this tutorial here. Instead, I’m going to give you a short overview of the multipeer connectivity framework.

So, MPC contains four important classes representing the following concepts:

  1. Peer (MCPeerID): A peer is actually a device, programmatically represented. It’s usually the first thing needs to be set up, as an object of this class is used as a parameter upon the initialization of the next classes’ instances. Also, it contains an important property, named displayName. This is the device name appearing to the other, nearby peers.
  2. Session (MCSession class): It’s the connection established between two peers, after the first one has invited the second, and of course the invitation has been accepted. A session regards two devices only. A third device cannot be connected to an existing session, instead another one is used.
  3. Browser (MCNearbyServiceBrowser class): The methods of this class are used to find other nearby devices and invite them to join a session. As a prerequisite, the other devices must advertise themselves. In this tutorial we’ll use this class to manually invite other devices.
  4. Advertiser (MCNearbyServiceAdvertiser): This class is responsible for advertising a device, meaning making the device visible or not to others, and for accepting or not invitations from other peers for connecting to sessions.

The logic of the multipeer connectivity framework is simple: A device (a peer) using its browser, searches for other devices around. As I said, a device must advertise itself so as to be discoverable. Once it finds one or more peers, it can send an invitation for connecting to a session. The invitation can be sent either automatically once a nearby peer is found, or after the user has decided to do so. Actually, this is totally up to the application that is being implemented, so there’s not a standard recipe. You will be the one to decide when you’ll send an invitation. In any case, once the invitation has been accepted, the session is established and then the two peers can send and receive data, resources, or streams.

My goal in this post is to show you how to programmatically browse, invite and connect to other peers. Note that what you’ll see next, it’s just a way of implementation. Obviously, you can use all the provided tools by the MPC in the way you want and perform your own implementation that suits to the application you build. What you’ll see it’s just a sample of how the MPC framework can be implemented and integrated purely programmatically from the beginning to the end, without using any pre-made view controller of the SDK. Hopefully, by the end of this tutorial, many of you may find some answers to what you seek.

Lastly, if you’ve never worked with the MPC framework before I encourage you to take a quick look at both the official documentation by Apple, and my previous tutorials, so you have an idea before you proceed. Having said that, let’s don’t waste any more time, and let’s dive in some programming aspects of the multipeer connectivity.

Read the full tutorial on Appcoda

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