Resuming Apps

It may be necessary for your app to resume from a background or closed state and re-establish connection with a previously connected device. There are many ways in which Connect SDK provides information to allow for this behavior.

ConnectableDevice ID

Each ConnectableDevice has a unique ID assigned to it upon creation. When that device is connected to, the device store saves information about each of the device's services. The unique ID persists across app launches by attributing service UUIDs to the unique device ID in the device store.


The ability to interact with an app requires some information to persist, including a session ID. This session ID may be required to close the app, as well as allow the app to accurately track certain state information.


The ability to communicate with a web app requires a LaunchSession object and/or the web app id.

Resuming most recent connection

In order to save & reconnect to a previously connected device, all you need to keep track of is the device's ID. Assuming you are using the ConnectableDeviceStore included with Connect SDK, previously connected devices will persist the same ID between app launches.

When your app restarts, you should immediately start discovery and listen for device found events from DiscoveryManager. In these events, you can check each device's ID and call connect on the previously connected device.

Important note about reconnecting

Just because your device has been discovered on the network doesn't mean that all of its services/capabilities are available. You will need to set a CapabilityFilter on DiscoveryManager or manually check the ConnectableDevice's capabilities before you call connect.

Save device ID to disk

ConnectableDevice *device; // device you've connected to

[[NSUserDefaults standardUserDefaults] forKey:@"recentDeviceId"];

// save right away before entering background
[NSUserDefaults standardUserDefaults] synchronize];

Reconnect to device

ConnectableDevice *mDevice;
NSString *mRecentDeviceId;

- (void) viewDidLoad {
    [super viewDidLoad];

    mRecentDeviceId = [[NSUserDefaults standardUserDefaults] objectForKey:@"recentDeviceId"];

    [[DiscoveryManager sharedManager] setCapabilityFilters:myCapabilityFilters];
    [[DiscoveryManager sharedManager] setDelegate:self];
    [[DiscoveryManager sharedManager] start];

- (void) discoveryManager:(DiscoveryManager *)manager didFindDevice:(ConnectableDevice *)device {
    if (mRecentDeviceId && !mDevice) {
        if ([ isEqualToString:mRecentDeviceId]) {
            mDevice = device;
            [device setDelegate:self];
            [device connect];

Resuming a web app session

Resuming a web app session is as simple as saving the WebAppSession's LaunchSession object before entering the background. It can even be serialized into a JSON object for easy cross-platform storage.

Save session info to disk

WebAppSession *webAppSession; // retrieved from WebAppLauncher launch success block

LaunchSession *launchSession = webAppSession.launchSession;
NSDictionary *launchSessionInfo = [launchSession toJSONObject];

[[NSUserDefaults standardUserDefaults] setObject:launchSessionInfo forKey:@"launchSession"];

// save right away before entering background
[NSUserDefaults standardUserDefaults] synchronize];

Re-create session after device is connected/ready

ConnectableDevice *device; // device that has been re-discovered & re-connected

NSDictionary *launchSessionInfo = (NSDictionary *) [[NSUserDefaults standardUserDefaults] objectForKey:@"launchSession"];
LaunchSession *launchSession = [LaunchSession launchSessionFromJSONObject:launchSessionInfo];

[device.webAppLauncher joinWebApp:launchSession
                          success:^(WebAppSession *webAppSession) { }
                          failure:^(NSError *) { } ];

Low-effort re-connection option

Alternatively, you could re-join your web app with just the web app id. This could have the side effect of generating new session information for your user, which may not be desired.

[device.webAppLauncher joinWebAppWithId:@"your web app id"
                                success:^(WebAppSession *webAppSession) { }
                                failure:^(NSError *) { } ];

See also