I'm trying to achieve the following scenario:
Open the app and connect to a BLE Peripheral. Working
Send the app to the background and keep the connection alive. Working
Turn off the BLE Peripheral and the app is notified of the disconnection. Working
Turn on the BLE Peripheral and the app is notified of the disconnection. Working
Turn off again the BLE Peripheral. Working
Wait 2 days with the app in background and turn on the BLE Peripheral, but the app does nothing. NOT Working
How can I achieve this last step? iOS kills the background apps when needed, but is there a way of getting notified when a previously-connected peripheral is discovered? I read something about CB State Restoration but I don't really know if this will solve this situation.
Core Bluetooth state preservation / restoration is exactly what you want. If your app is suspended, it will start you app if a peripheral connects / disconnects or a notification arrives. It is however broken by design in the way that your app will stop being woken up if Bluetooth is restarted for any reason. Examples are Bluetooth crashes (happens every now and then), if the user toggles Bluetooth or flight mode, or if the phone is restarted.
Related
I have an app that uses Bluetooth (BLE). All BLE communication works fine. State restoration is also implemented and works well. The app has automatic re-connection implementation: whenever the CBError.peripheralDisconnected error occurs, the app tries to reconnect to the peripheral by calling cbCentralManager.connect(cbPeripheral).
Since iOS 15/16 there is a problem. Let's assume that the app is connected to a specific BLE device. I turn off the device (at this moment the automatic re-connection started) and move the app to the background. After several hours (e.g. over the night) I turn on the BLE device and the connection isn't established. I can see this on my Bluetooth device and in the iOS Bluetooth settings. Only when I open the app again, the connection is established immediately. Nothing happens in between. Only the connect call of the CBCentralManager after the Bluetooth device is turned off. The whole thing works when the app is in the background for 3 - 5 hours. If it is over approx. 5 hours, the connection is no longer established as soon as the app is in the background.
At first I thought that the app or the BLE connection is simply killed by the system after a long time. However, the state restoration for Bluetooth is implemented and works (I tested it).
Does anyone have any idea what this could be? Are there perhaps any new settings for state restoration or Bluetooth background mode since iOS 15/16?
Many thanks in advance.
I have an iPhone app that receive BLE info from a particular device. The device sends data to my app anytime it has something to report, and the transmission rate is about 2K Bytes per second.
The problem is that my app can be killed in the background mode by iOS and I can get no indication about this. If the device start to send ble data after my app is killed, my app can only get the last data packet after it is woken up by the system and lost all the data during the wake up procedure.
How can I get all the BLE data after my app is woken up and restored by the system?
PS: I have added Bluetooth-central under UIBackgroundModes in the Info.plist. In background mode didUpdateValueForCharacteristic: method is being called. Also, a CBCentralManagerOptionRestoreIdentifierKey is specified while I construct the CBCentralManager.
On iOS you can ensure that your app isn't completely killed by the system by using State Preservation and Restoration. Please have a look at the following link for more info:-
Core Bluetooth Background Processing for iOS
However, please note that you cannot use this if you force kill the app. There's more information about this in the following question:-
BLE device keep connect with iPhone when application terminate
I was searching for my Bluetooth problem a few days but I did not find any useful solution. I would like reading advertising data more precisely manufacturing data from peripheral devices via ios application when it is in the background. In my case, the peripheral devices are Nordic nrf51822 chips and a central device is ios phone. I have successfully implemented the Bluetooth background mode and it works well on the ios device. The Event handler DiscoveredPeripheral is called when the new peripheral device is discovered. But the problem is that it is called only first-time the peripheral device becomes visible. If I turn off and on the peripheral device the DiscoverdPeripheral event is not called anymore. I know that this is ios restriction, but I do not know how can I handle this ios limitation. In the end, I would like that app in the background starts scanning for peripheral devices with specific UUID periodically, for example, every 10minutes. At this point, I would like to ask if this scenario is possible to implement in ios if so I appreciate for any help.
The Event handler DiscoveredPeripheral is called when the new peripheral device is discovered.
This isn't correct. It will only be called once per call to scanForPeripherals. When the device connects, you should stop scanning. When the device disconnects, which you should see as centralManager(_:didDisconnectPeripheral:error:), you can begin scanning again.
Even better, if you only want to reconnect to the same device, don't scan at all. Just call connect for that peripheral UUID. It will continue running while you're in the background and wake you up when the connect succeeds.
To push this further, implement Bluetooth State Restoration, which will allow you to automatically reconnect even after reboots.
I am planning to develop an iOS application using CoreBluetooth framework which monitors a pedometer peripheral continuously and counts the footsteps.
I know that if backgroud execution mode is set to BLE Central, the application will continue to receive BLE events even in the background.
Apple documentation states that in case the app gets terminated due to low memory, the system can keep track of BLE events for a particular Central Manager if state preservation and restoration is adopted.
Assume I have an iOS application that operates in Central mode. The app is subscribed to receive notification from a Pedometer when ever the footstep characteristic changes.
I have adopted the following in my app.
BLE Central background mode
BLE State preservation/restoration for Central Manager
I start my app, Scan, Pair and Connect to the pedometer and the app starts receiving footsteps.
My Questions:
Now if the iPhone reboots, Will I continue to receive BLE events so that my app will be launched in the background without the user having to manually launch the application again and connect to the pedometer?
If the app is terminated by the user explicitly using the multitasking gesture, Will the app be able to receive BLE events without the user having to manually launch the application again and connect to the pedometer?
Is there a way to launch my application on iOS boot up?
Now if the iPhone reboots, Will I continue to receive BLE events so that my app will be launched in the background without the user having to manually launch the application again and connect to the pedometer?
Your app won't receive BLE events because all apps are started in the terminated state after a reboot (despite remaining in the app switcher). The user will have to manually launch your app at least once after reboot in order for it to use BLE.
If the app is terminated by the user explicitly using the multitasking gesture, Will the app be able to receive BLE events without the user having to manually launch the application again and connect to the pedometer?
Same as above, the app has entered the terminated state, so it won't be able to communicate using BLE until it is explicitly launched again.
Is there a way to launch my application on iOS boot up?
iOS doesn't provide any way to launch your application on boot.
The one exception to all of this that I can find is iBeacons. If your app registers to receive updates for a specific iBeacon, iOS will launch your app when it finds it (even after a reboot or if the user explicitly kills it from the switcher). When you get the iBeacon callback you can start all your BLE logic and it will then run in the background per usual. Of course this means you need to advertise as an iBeacon on your pedometer, which may or may not be feasible.
Bear in mind the detection of the iBeacon is pretty finicky, especially after a reboot. You have little guarantee as to how fast or even if you will be delivered the iBeacon callback to start your app. But it's something.
Source
Is there any way to "wake-up" (relaunch) an iOS application (a background task actually, not to show the application) whenver a bluetooth device is connected?
For example, the iOS OS kills the application due to memory lack. Then a couple of hours later the user connects his bluetooth device. Can the iOS notify my application that the bluetooth device is connected and run a background task?
In Android I see that I can create a BroadcastReceiver that is registered for when a bluetooth device is connected. I need something equivalent to that for iOS.
If you have a pending connect for your BLE peripheral and you have specified BLE central background mode then yes, your app will be relaunched. You also need to implement state preservation and restoration as described in the Core Bluetooth programming guide in the event that your app is actually killed (not just in the background).
Note that in iOS a user cannot connect to a BLE peripheral directly - your app is responsible for identifying the target BLE peripheral and issuing the connect command. This is described in the programming guide.