邀请多对等连接中的对等方时偶尔发生故障

Question

我有一个已发布的应用程序，它使用多人连接活动定期发送少量数据。我正在使用MCNearbyServiceAdvertiser和MCNearbeServiceBrowser。当我测试时，一切都很好。然而，我一直收到来自我的用户的崩溃报告，数量不多，但足以引起我的注意。

*** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '*** -   [__NSPlaceholderDictionary initWithObjects:forKeys:count:]: attempt to insert nil object from objects[2]'
Last Exception Backtrace:
0   CoreFoundation                       0x30b8cf03 __exceptionPreprocess + 131
1   libobjc.A.dylib                      0x3b321ce7 objc_exception_throw + 36
2   CoreFoundation                       0x30acad3f -[__NSPlaceholderDictionary initWithObjects:forKeys:count:] + 532
3   CoreFoundation                       0x30acab03 +[NSDictionary dictionaryWithObjects:forKeys:count:] + 48
4   MultipeerConnectivity                0x32420e87 -[MCNearbyServiceBrowser syncInvitePeer:toSession:withContext:timeout:] + 452
5   MultipeerConnectivity                0x324220cf __67-[MCNearbyServiceBrowser invitePeer:toSession:withContext:timeout:]_block_invoke + 84
6   libdispatch.dylib                    0x3b80ad53 _dispatch_call_block_and_release + 8
7   libdispatch.dylib                    0x3b80fcbd _dispatch_queue_drain + 486
8   libdispatch.dylib                    0x3b80cc6f _dispatch_queue_invoke + 40
9   libdispatch.dylib                    0x3b8105f1 _dispatch_root_queue_drain + 74
10  libdispatch.dylib                    0x3b8108dd _dispatch_worker_thread2 + 54
11  libsystem_pthread.dylib              0x3b93bc17 _pthread_wqthread + 296
12  libsystem_pthread.dylib              0x3b93badc start_wqthread + 6

尽管付出了很多努力，我还是没能重现那场车祸。我试过把应用程序放在后台，断开连接，打开和关闭网络等等。通常情况下，每次都能很好地重新连接，有时是在点击"重新连接按钮"后，但没有崩溃。有人知道原因吗？或者至少知道如何迫使这种情况发生？

浏览器端如下所示：

-(void)setUpPP{
  self.PPid = [[MCPeerID alloc] initWithDisplayName:@"PhotoFinish"];
  self.SSid = [[MCPeerID alloc] init];
  self.PPsession = [[MCSession alloc] initWithPeer:self.PPid securityIdentity:nil encryptionPreference:MCEncryptionNone];
  self.PPsession.delegate = self;
  self.PPbrowser = [[MCNearbyServiceBrowser alloc] initWithPeer:self.PPid serviceType:@"sprinttimer" ];
  self.PPbrowser.delegate = self;
  [self.PPbrowser startBrowsingForPeers];
}
-(IBAction)startSync:(id)sender {
  [self.PPbrowser invitePeer:self.SSid toSession:self.PPsession withContext:nil timeout:10];
}
-(void)session:(MCSession *)session peer:(MCPeerID *)peerID didChangeState:(MCSessionState)state{
  NSString *displayString;
  if (state == MCSessionStateConnected && self.PPsession) {
    displayString=@"Start Sender connected";
  } else if (state == MCSessionStateNotConnected && self.PPsession) {
    displayString=@"No Start Sender in range";
    connected=NO;
  }
 [self performSelectorOnMainThread:@selector(displaySync:) withObject:displayString waitUntilDone:NO];
}
-(void)browser:(MCNearbyServiceBrowser *)browser foundPeer:(MCPeerID *)peerID withDiscoveryInfo:(NSDictionary *)info{
  self.SSid=peerID;
}

Answer 1

知道什么操作触发startSync:会很有帮助，但在setUpPP中，您正在将一个无意义的MCPeerID实例（没有displayName）分配给self.SSid，因此如果在self.SSid获得分配给它的真正MCPeerID之前调用startSync:，我可以看到崩溃的发生。

我的建议是从self.SSid作为nil开始，并确保除非该属性有值，否则不会发送邀请。更进一步说，我不会依赖于一个属性来存储MCPeerID，它可能在调用startSync:之前更改其值。