您的应用可以使用与订阅附近其他设备发布的消息相同的机制来订阅蓝牙低功耗 (BLE) 信标消息。
默认情况下,信标订阅仅在您的应用在前台运行时有效。当您的应用转到后台时,订阅会自动停止扫描信标。如需详细了解如何启用后台扫描,请参阅后台扫描。
如需订阅信标,请在订阅参数中将 deviceTypesToDiscover
参数设置为 kGNSDeviceBLEBeacon
。以下代码段展示了如何执行此操作:
Objective-C
id<GNSSubscription> beaconSubscription = [messageManager
subscriptionWithMessageFoundHandler:myMessageFoundHandler
messageLostHandler:myMessageLostHandler
paramsBlock:^(GNSSubscriptionParams *params) {
params.deviceTypesToDiscover = kGNSDeviceBLEBeacon;
}];
Swift
let beaconSubscription = messageManager.subscriptionWithMessageFoundHandler(
myMessageFoundHandler, messageLostHandler: myMessageLostHandler,
paramsBlock: { (params: GNSSubscriptionParams!) in
params.deviceTypesToDiscover = .BLEBeacon
})
上述订阅仅会发现您的项目拥有的信标,并会从这些信标接收所有消息。如果您想接收来自使用其他命名空间注册的信标的消息,则可以在订阅参数中传递命名空间。同样,如果您需要特定类型的消息,还可以传递消息类型以进行过滤。以下代码段展示了如何执行此操作:
Objective-C
id<GNSSubscription> beaconSubscription = [messageManager
subscriptionWithMessageFoundHandler:myMessageFoundHandler
messageLostHandler:myMessageLostHandler
paramsBlock:^(GNSSubscriptionParams *params) {
params.deviceTypesToDiscover = kGNSDeviceBLEBeacon;
params.messageNamespace = @"com.mycompany.mybeaconservice";
params.type = @"mybeacontype";
}];
Swift
let beaconSubscription = messageManager.subscriptionWithMessageFoundHandler(
myMessageFoundHandler, messageLostHandler: myMessageLostHandler,
paramsBlock: { (params: GNSSubscriptionParams!) in
params.deviceTypesToDiscover = .BLEBeacon
params.messageNamespace = "com.mycompany.mybeaconservice"
params.type = "mybeacontype"
})
默认情况下,信标订阅会扫描两种信标(Eddystone 和 iBeacon)。启用 iBeacon 扫描后,系统会提示用户授予应用使用其位置数据的权限。应用的 Info.plist
必须包含 NSLocationWhenInUseUsageDescription
键,并简要说明使用位置信息的原因。如需了解详情,请参阅 Apple 文档。
如果您只想扫描 Eddystone 信标,可以在 GNSBeaconStrategy
中停用 iBeacon 扫描,这样 iOS 就不会向用户请求使用位置信息的权限。以下代码段展示了如何为上述原始订阅停用 iBeacon 扫描:
Objective-C
id<GNSSubscription> beaconSubscription = [messageManager
subscriptionWithMessageFoundHandler:myMessageFoundHandler
messageLostHandler:myMessageLostHandler
paramsBlock:^(GNSSubscriptionParams *params) {
params.deviceTypesToDiscover = kGNSDeviceBLEBeacon;
params.beaconStrategy =
[GNSBeaconStrategy strategyWithParamsBlock:^(GNSBeaconStrategyParams *params) {
params.includeIBeacons = NO;
};
}];
Swift
let beaconSubscription = messageManager.subscriptionWithMessageFoundHandler(
myMessageFoundHandler, messageLostHandler: myMessageLostHandler,
paramsBlock: { (params: GNSSubscriptionParams!) in
params.deviceTypesToDiscover = .BLEBeacon
params.beaconStrategy =
GNSBeaconStrategy(paramsBlock: { (params: GNSBeaconStrategyParams!) in
params.includeIBeacons = false
})
})
默认情况下,低功耗扫描处于启用状态,这有时会导致在查找 Eddystone 信标时导致较长的延迟时间。停用低功耗模式后,系统会使用 iBeacon 扫描来帮助查找 Eddystone 信标,从而缩短此类延迟时间。不过,这会导致电池耗电量增加,并且 iOS 会请求用户授予使用位置信息的权限。
以下代码段展示了如何在扫描 Eddystone 信标时停用低功耗模式。
Objective-C
id<GNSSubscription> beaconSubscription = [messageManager
subscriptionWithMessageFoundHandler:myMessageFoundHandler
messageLostHandler:myMessageLostHandler
paramsBlock:^(GNSSubscriptionParams *params) {
params.deviceTypesToDiscover = kGNSDeviceBLEBeacon;
params.beaconStrategy =
[GNSBeaconStrategy strategyWithParamsBlock:^(GNSBeaconStrategyParams *params) {
params.includeIBeacons = NO;
params.lowPowerPreferred = NO;
};
}];
Swift
let beaconSubscription = messageManager.subscriptionWithMessageFoundHandler(
myMessageFoundHandler, messageLostHandler: myMessageLostHandler,
paramsBlock: { (params: GNSSubscriptionParams!) in
params.deviceTypesToDiscover = .BLEBeacon
params.beaconStrategy =
GNSBeaconStrategy(paramsBlock: { (params: GNSBeaconStrategyParams!) in
params.includeIBeacons = false
params.lowPowerPreferred = false
})
})
扫描 iBeacon 时,iOS 位置信息权限对话框会在显示“附近”权限对话框之前显示。如需替换此对话框(例如,提供“预检”对话框来说明为何需要位置信息权限),请在订阅参数中将 permissionRequestHandler
设置为自定义块。以下代码段展示了如何执行此操作:
Objective-C
id<GNSSubscription> beaconSubscription = [messageManager
subscriptionWithMessageFoundHandler:myMessageFoundHandler
messageLostHandler:myMessageLostHandler
paramsBlock:^(GNSSubscriptionParams *params) {
params.deviceTypesToDiscover = kGNSDeviceBLEBeacon;
params.permissionRequestHandler = ^(GNSPermissionHandler permissionHandler) {
// Show your custom dialog here, and don't forget to call permissionHandler after it is dismissed
permissionHandler(userGavePermission);
};
}];
Swift
let beaconSubscription = messageManager.subscriptionWithMessageFoundHandler(
myMessageFoundHandler, messageLostHandler: myMessageLostHandler,
paramsBlock: { (params: GNSSubscriptionParams!) in
params.deviceTypesToDiscover = .BLEBeacon
params.permissionRequestHandler = { (permissionHandler: GNSPermissionHandler!) in
// Show your custom dialog here, and don't forget to call permissionHandler after it is dismissed
permissionHandler(userGavePermission);
}
})
后台扫描
由于信标扫描使用 BLE,因此它可以在后台运行。在决定使用后台模式时,请注意以下事项:
- 使用后台 BLE 会增加额外的电池成本。费用很低,但您应该先进行衡量,然后再决定是否使用后台模式。
- 如果已启用 iBeacon 扫描或停用了低功耗模式,iOS 会请求用户授予在后台使用位置信息的权限。
如需在后台启用信标扫描,还要执行以下额外步骤:
通过传入正确配置的
GNSBeaconStrategy
对象,为订阅启用后台模式。以下代码段展示了如何执行此操作:Objective-C
id<GNSSubscription> beaconSubscription = [messageManager subscriptionWithMessageFoundHandler:myMessageFoundHandler messageLostHandler:myMessageLostHandler paramsBlock:^(GNSSubscriptionParams *params) { params.deviceTypesToDiscover = kGNSDeviceBLEBeacon; params.beaconStrategy = [GNSBeaconStrategy strategyWithParamsBlock:^(GNSBeaconStrategyParams *params) { params.allowInBackground = YES; }]; }];
Swift
let beaconSubscription = messageManager.subscriptionWithMessageFoundHandler( myMessageFoundHandler, messageLostHandler: myMessageLostHandler, paramsBlock: { (params: GNSSubscriptionParams!) in params.deviceTypesToDiscover = .BLEBeacon params.beaconStrategy = GNSBeaconStrategy(paramsBlock: { (params: GNSBeaconStrategyParams!) in params.allowInBackground = true }) })
将所需的条目添加到应用的
Info.plist
:UIBackgroundModes
个条目:bluetooth-central
,用于在后台进行 BLE 扫描。location
,用于在高功耗模式下在后台进行 iBeacon 扫描。 如果您仅为 Eddystone 信标执行低功耗扫描,则可以忽略此字段。
NSLocationAlwaysUsageDescription
字符串,说明您将在后台跟踪用户位置的原因。例如,“需要您的位置信息扫描,才能在后台扫描信标”。如需了解详情,请参阅 Apple 文档。如果您仅为 Eddystone 信标执行低功耗扫描,则可以忽略此字段。
用户能否在您的应用中启用或停用后台扫描功能?如果是这样,您应将后台模式值保存到
NSUserDefaults
,因为 iOS 可能会随时终止您的应用在后台运行。您的应用应执行以下操作:- 每当用户更改后台模式值时,都会将其保存到
NSUserDefaults
。 - 启动时,从
NSUserDefaults
读取该消息,并在启用了后台模式的情况下恢复信标订阅。
- 每当用户更改后台模式值时,都会将其保存到