LiveQuery stops and does not restart in the background

cbaker6 · February 7, 2022, 3:03pm

The Swift SDK is designed for SwiftUI and MVVM out-of-the-box. A LiveQuery Subscription is already a View Model as discussed in the documentation, so using subscribeCallback in the manner you are using it is the long way:

github.com

parse-community/Parse-Swift/blob/c8252bcda8ea72c5d2b274df7a76ee289819f9ed/Sources/ParseSwift/LiveQuery/Subscription.swift#L20-L70


      
          open class Subscription<T: ParseObject>: QueryViewModel<T>, QuerySubscribable {
          
              /// Updates and notifies when there's a new event related to a specific query.
              open var event: (query: Query<T>, event: Event<T>)? {
                  willSet {
                      if newValue != nil {
                          subscribed = nil
                          unsubscribed = nil
                          DispatchQueue.main.async {
                              self.objectWillChange.send()
                          }
                      }
                  }
              }
          
              /// Updates and notifies when a subscription request has been fulfilled and if it is new.
              open var subscribed: (query: Query<T>, isNew: Bool)? {
                  willSet {
                      if newValue != nil {
                          unsubscribed = nil

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Cloud Functions and every Query can be used directly as a View Model without any additional code as well. The Playgrounds shows how to use a LiveQuery as a View Model directly:

github.com

parse-community/Parse-Swift/blob/c8252bcda8ea72c5d2b274df7a76ee289819f9ed/ParseSwift.playground/Pages/19 - SwiftUI - LiveQuery.xcplaygroundpage/Contents.swift#L65-L116


      
          //: Create a query just as you normally would.
          var query = GameScore.query("points" < 11)
          
          //: To use subscriptions inside of SwiftUI
          struct ContentView: View {
          
              //: A LiveQuery subscription can be used as a view model in SwiftUI
              @ObservedObject var subscription = query.subscribe!
          
              var body: some View {
                  VStack {
          
                      if subscription.subscribed != nil {
                          Text("Subscribed to query!")
                      } else if subscription.unsubscribed != nil {
                          Text("Unsubscribed from query!")
                      } else if let event = subscription.event {
          
                          //: This is how you register to receive notifications of events related to your LiveQuery.
                          switch event.event {

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I discuss and show examples on how to make sophisticated View Models leveraging subscriptions and standard queries by conforming and subclassing to what the Swift SDK provides: