In part 1 of my series about the iOS Multipeer Connectivity Framework I concluded that my solution to setup a session between 2 peers without user interaction was not working. This was caused by the mutual invitation issue: A peer continues to invite the peer that it was already connected with.
In this post I wil come up with a solution for the mutual invitation issue. You can download the source code here.
The relevant snippet is in the MCNearbyServiceBrowserDelegate.
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- (void)browser:(MCNearbyServiceBrowser *)browser foundPeer:(MCPeerID *)peerID withDiscoveryInfo:(NSDictionary *)info { NSLog(@"Browser %@ found %@", self.peerId.displayName, peerID.displayName); NSLog(@"Browser %@ invites %@ to connect", self.peerId.displayName, peerID.displayName); [self.browser invitePeer:peerID toSession:self.session withContext:nil timeout:10]; } |
This method is called when a browser finds a peer. As soon as a browser has found a peer it invites the peer to connect. We are going to solve the mutual invitation issue by establishing a rule: “I will only invite a peer if the hash value of my peerID is smaller than the hash value of the other peerID”. Both peers will apply the same rule, so it is guaranteed that only one of them will send the invitation.
In code this can be expressed as follows:
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- (void)browser:(MCNearbyServiceBrowser *)browser foundPeer:(MCPeerID *)peerID withDiscoveryInfo:(NSDictionary *)info { NSLog(@"Browser %@ found %@", self.peerId.displayName, peerID.displayName); // Should I invite the peer or should the peer invite me? Let the decision be based on the comparison of the hash values of the peerId. BOOL shouldInvite = self.peerId.hash < peerID.hash; if (shouldInvite) { // I will invite the peer, the remote peer will NOT invite me. NSLog(@"Browser %@ invites %@ to connect", self.peerId.displayName, peerID.displayName); [self.browser invitePeer:peerID toSession:self.session withContext:nil timeout:10]; } else { // I will NOT invite the peer, the remote peer will invite me. NSLog(@"Browser %@ does not invite %@ to connect", self.peerId.displayName, peerID.displayName); } } |
Now let’s run a test
Again, we are going to connect the 2 peers, the simulator and my iPhone. Below you can see the result. I will show you the original logs, including the mutual invitation issue, and the logs with the fix described above, so you can compare them.
Log with mutual invitation issue
Log after application of the fix
As you can see steps 1 to 6 are exactly identical for both scenario’s. The big difference is at step 7. The log with the fix shows that the simulator does NOT invite the iPhone, thanks to the rule that comers the hash values of the peerID’s. Therefore step 8 and 9 will not be triggered either, and the peers are connected.
Conclusion
We can conclude that we solved the mutual invitation issue. Peers can now create a session without any user interaction. I will continue with the Multipeer Connectivity Framework research and will post new articles if I encounter further issues.