Operation Expiration Handling
Every operation should have an expiration time. An expired operation cannot be confirmed nor rejected - the server will return an error with the appropriate error (see Operation errors).
Retrieving expiration time
WMTUserOperation
The WMTUserOperation provided by the WMTOperations service has its expiration time inside the operationExpires property.
Custom operation
If you’re creating your own custom operation by implementing the WMTOperation protocol, you need to provide the expiration time by yourself. The expiration time is optional because it’s not part of the operation signature.
Handling via push notifications
If the device is registered to receive push notifications, it will receive an operationFinished notification with the timeout result when the operation expires.
Operation list should be refreshed on such notification.
Please be aware that push notifications are not guaranteed to be received. There are several scenarios where push notification delivery will fail, such as:
- user didn’t grant notification permission to your app
- network error
- notification token has expired and is waiting for renewal
- …
Local handling
Since push notifications are not guaranteed to be delivered, you should implement a mechanism that will refresh the list to validate if it was expired on the server too.
Server and client device time could differ! You should never remove the operation just locally, but refresh the operation list instead.
WMTOperationExpirationWatcher
Utility class that will observe operations and informs you when it expired.
Sample implementation:
// Sample implementation of a class that's using the WMTOperationExpirationWatcher
class MyOperationsService: WMTOperationsDelegate, WMTOperationExpirationWatcherDelegate {
private let ops: WMTOperations
private let expirationWatcher = WMTOperationExpirationWatcher()
init(ops: WMTOperations) {
self.ops = ops
// set delegates to observer operation and expiration results
self.ops.delegate = self
self.expirationWatcher.delegate = self
}
func refreshOperations() {
ops.refreshOperations()
}
func operationsLoading(loading: Bool) {
// process operations loading state change
// not needed for the sample
}
func operationsFailed(error: WMTError) {
// process operations loading state change
// not needed for the sample
}
func operationsChanged(operations: [UserOperation], removed: [UserOperation], added: [UserOperation]) {
// simplified but working example how operations can be observed for expiration
expirationWatcher.removeAll()
expirationWatcher.add(operations)
// process operations
// ...
}
// MARK: - WMTOperationExpirationWatcherDelegate
func operationsExpired(_ expiredOperations: [WMTExpirableOperation]) {
// some operation expired, refresh the list
refreshOperations()
// this behavior could be improved for example with
// checking if the expired operations is currently displayed etc..
}
}