Core Bluetooth does not find peripherals when scanning for a specific CBUUID

Question

It seems that this question was “answered” here , but without any code to show what they did differently, I need to ask a new question.

I have my own code with the same behavior when scanning for specific CBUUIDs using Core Bluetooth CBCentralManager in OS X does not detect an iOS device acting as a peripheral device with CBPeripheralManager (unless it and its services were previously discovered). To find out if this is not the case in my code, I downloaded a sample Apple code . Running the sample code on two iOS devices works as intended, but when you copy the CBCentralManager code to the OS X application, it cannot find the iOS device.

I downloaded the Xcode project for an OS X application, hosted on WikiUpload , as it seems the least tricky. There is also a copy on my hosting if people prefer.

The AppDelegate.m code has also been added here in the OS X project (CoreBluetooth infrastructure is connected in the project):

#import <CoreBluetooth/CoreBluetooth.h> @interface AppDelegate () <CBCentralManagerDelegate, CBPeripheralDelegate> @property (strong, nonatomic) CBCentralManager *centralManager; @property (strong, nonatomic) CBPeripheral *discoveredPeripheral; @property (strong, nonatomic) NSMutableData *data; @property (weak) IBOutlet NSWindow *window; @end @implementation AppDelegate @synthesize centralManager = _centralManager, discoveredPeripheral = _discoveredPeripheral, data = _data; - (void)applicationDidFinishLaunching:(NSNotification *)aNotification { // Insert code here to initialize your application // Start up the CBCentralManager _centralManager = [[CBCentralManager alloc] initWithDelegate:self queue:nil]; // And somewhere to store the incoming data _data = [[NSMutableData alloc] init]; } - (void)applicationWillTerminate:(NSNotification *)aNotification { // Insert code here to tear down your application } #pragma mark - Central Methods /** centralManagerDidUpdateState is a required protocol method. * Usually, you'd check for other states to make sure the current device supports LE, is powered on, etc. * In this instance, we're just using it to wait for CBCentralManagerStatePoweredOn, which indicates * the Central is ready to be used. */ - (void)centralManagerDidUpdateState:(CBCentralManager *)central { if (central.state != CBCentralManagerStatePoweredOn) { // In a real app, you'd deal with all the states correctly return; } // The state must be CBCentralManagerStatePoweredOn... // ... so start scanning [self scan]; } /** Scan for peripherals - specifically for our service 128bit CBUUID */ - (void)scan { // This brings up nothing, unlike on iOS where it finds the device straight away [self.centralManager scanForPeripheralsWithServices:@[[CBUUID UUIDWithString:TRANSFER_SERVICE_UUID]] options:@{ CBCentralManagerScanOptionAllowDuplicatesKey : @YES }]; // [self.centralManager scanForPeripheralsWithServices:nil // options:@{ CBCentralManagerScanOptionAllowDuplicatesKey : @YES }]; NSLog(@"Scanning started"); } /** This callback comes whenever a peripheral that is advertising the TRANSFER_SERVICE_UUID is discovered. * We check the RSSI, to make sure it close enough that we're interested in it, and if it is, * we start the connection process */ - (void)centralManager:(CBCentralManager *)central didDiscoverPeripheral:(CBPeripheral *)peripheral advertisementData:(NSDictionary *)advertisementData RSSI:(NSNumber *)RSSI { NSLog(@"Discovered %@ at %@", peripheral.name, RSSI); //Took out RSSI check if (self.discoveredPeripheral != peripheral) { // Save a local copy of the peripheral, so CoreBluetooth doesn't get rid of it self.discoveredPeripheral = peripheral; // And connect NSLog(@"Connecting to peripheral %@", peripheral); [self.centralManager connectPeripheral:peripheral options:nil]; } } /** If the connection fails for whatever reason, we need to deal with it. */ - (void)centralManager:(CBCentralManager *)central didFailToConnectPeripheral:(CBPeripheral *)peripheral error:(NSError *)error { NSLog(@"Failed to connect to %@. (%@)", peripheral, [error localizedDescription]); [self cleanup]; } /** We've connected to the peripheral, now we need to discover the services and characteristics to find the 'transfer' characteristic. */ - (void)centralManager:(CBCentralManager *)central didConnectPeripheral:(CBPeripheral *)peripheral { NSLog(@"Peripheral Connected"); // Stop scanning [self.centralManager stopScan]; NSLog(@"Scanning stopped"); // Clear the data that we may already have [self.data setLength:0]; // Make sure we get the discovery callbacks peripheral.delegate = self; // Search only for services that match our UUID [peripheral discoverServices:@[[CBUUID UUIDWithString:TRANSFER_SERVICE_UUID]]]; } /** The Transfer Service was discovered */ - (void)peripheral:(CBPeripheral *)peripheral didDiscoverServices:(NSError *)error { if (error) { NSLog(@"Error discovering services: %@", [error localizedDescription]); [self cleanup]; return; } // Discover the characteristic we want... // Loop through the newly filled peripheral.services array, just in case there more than one. for (CBService *service in peripheral.services) { [peripheral discoverCharacteristics:@[[CBUUID UUIDWithString:TRANSFER_CHARACTERISTIC_UUID]] forService:service]; } } /** The Transfer characteristic was discovered. * Once this has been found, we want to subscribe to it, which lets the peripheral know we want the data it contains */ - (void)peripheral:(CBPeripheral *)peripheral didDiscoverCharacteristicsForService:(CBService *)service error:(NSError *)error { // Deal with errors (if any) if (error) { NSLog(@"Error discovering characteristics: %@", [error localizedDescription]); [self cleanup]; return; } // Again, we loop through the array, just in case. for (CBCharacteristic *characteristic in service.characteristics) { // And check if it the right one if ([characteristic.UUID isEqual:[CBUUID UUIDWithString:TRANSFER_CHARACTERISTIC_UUID]]) { // If it is, subscribe to it [peripheral setNotifyValue:YES forCharacteristic:characteristic]; } } // Once this is complete, we just need to wait for the data to come in. } /** This callback lets us know more data has arrived via notification on the characteristic */ - (void)peripheral:(CBPeripheral *)peripheral didUpdateValueForCharacteristic:(CBCharacteristic *)characteristic error:(NSError *)error { if (error) { NSLog(@"Error discovering characteristics: %@", [error localizedDescription]); return; } NSString *stringFromData = [[NSString alloc] initWithData:characteristic.value encoding:NSUTF8StringEncoding]; // Have we got everything we need? if ([stringFromData isEqualToString:@"EOM"]) { // We have, so show the data, //[self.textview setText:[[NSString alloc] initWithData:self.data encoding:NSUTF8StringEncoding]]; NSLog(@"Text: %@", [[NSString alloc] initWithData:self.data encoding:NSUTF8StringEncoding]); // Cancel our subscription to the characteristic [peripheral setNotifyValue:NO forCharacteristic:characteristic]; // and disconnect from the peripehral [self.centralManager cancelPeripheralConnection:peripheral]; } // Otherwise, just add the data on to what we already have [self.data appendData:characteristic.value]; // Log it NSLog(@"Received: %@", stringFromData); } /** The peripheral letting us know whether our subscribe/unsubscribe happened or not */ - (void)peripheral:(CBPeripheral *)peripheral didUpdateNotificationStateForCharacteristic:(CBCharacteristic *)characteristic error:(NSError *)error { if (error) { NSLog(@"Error changing notification state: %@", error.localizedDescription); } // Exit if it not the transfer characteristic if (![characteristic.UUID isEqual:[CBUUID UUIDWithString:TRANSFER_CHARACTERISTIC_UUID]]) { return; } // Notification has started if (characteristic.isNotifying) { NSLog(@"Notification began on %@", characteristic); } // Notification has stopped else { // so disconnect from the peripheral NSLog(@"Notification stopped on %@. Disconnecting", characteristic); [self.centralManager cancelPeripheralConnection:peripheral]; } } /** Once the disconnection happens, we need to clean up our local copy of the peripheral */ - (void)centralManager:(CBCentralManager *)central didDisconnectPeripheral:(CBPeripheral *)peripheral error:(NSError *)error { NSLog(@"Peripheral Disconnected"); self.discoveredPeripheral = nil; // We're disconnected, so start scanning again [self scan]; } /** Call this when things either go wrong, or you're done with the connection. * This cancels any subscriptions if there are any, or straight disconnects if not. * (didUpdateNotificationStateForCharacteristic will cancel the connection if a subscription is involved) */ - (void)cleanup { // Don't do anything if we're not connected if (!self.discoveredPeripheral.isConnected) { return; } // See if we are subscribed to a characteristic on the peripheral if (self.discoveredPeripheral.services != nil) { for (CBService *service in self.discoveredPeripheral.services) { if (service.characteristics != nil) { for (CBCharacteristic *characteristic in service.characteristics) { if ([characteristic.UUID isEqual:[CBUUID UUIDWithString:TRANSFER_CHARACTERISTIC_UUID]]) { if (characteristic.isNotifying) { // It is notifying, so unsubscribe [self.discoveredPeripheral setNotifyValue:NO forCharacteristic:characteristic]; // And we're done. return; } } } } } } // If we've got this far, we're connected, but we're not subscribed, so we just disconnect [self.centralManager cancelPeripheralConnection:self.discoveredPeripheral]; } 

And in AppDelegate.h there are UUID definitions:

 #ifndef LE_Transfer_TransferService_h #define LE_Transfer_TransferService_h #define TRANSFER_SERVICE_UUID @"E20A39F4-73F5-4BC4-A12F-17D1AD07A961" #define TRANSFER_CHARACTERISTIC_UUID @"08590F7E-DB05-467E-8757-72F6FAEB13D4" #endif 

What is the problem? According to the above question, the service should be part of the proposal package, but as far as I can see, exactly what the iOS peripheral does with

 [self.peripheralManager startAdvertising:@{ CBAdvertisementDataServiceUUIDsKey : @[[CBUUID UUIDWithString:TRANSFER_SERVICE_UUID]] }]; 

Answer 1

CoreBluetooth can be very annoying. Here are a few things to try:

# 1: the peripheral device that was connected to the ad stop. If you are successfully connecting to the periphery, you need to restart the advertisement.

# 2: iOS caches detected status and services provided. There is no software way to update / clear the cache. Try disabling BT on your iOS device and Mac and turning it back on. Then try another connection.

# 3: Problem with your UUIDs. Try scanning for peripherals with the UUID parameter set to nil. Then you should find all peripheral devices in the range.

# 4: BT connection on Mac can be very successful if Wi-Fi is turned on. Try disabling Wi-Fi on your Mac and try again. I found that BTLE is completely unsuitable with Wi-Fi support, so I had to use ethernet when I do any BTLE-dev on my MacBook.