Create Subscription and Render Result

So let's define the graphql subscription to be used.

Open OnlineFragment.kt and update following code,

OnlineFragment.kt

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+    private lateinit var onlineUsersSubscriptionQuery: GetOnlineUsersSubscription
    private lateinit var lastSeenMutation: UpdateLastSeenMutation
+    private var onlineUsersSubscription: ApolloSubscriptionCall<GetOnlineUsersSubscription.Data>? = null

+    // Queries and mutations
+    private fun subscribeOnlineUsers() {
+        // Init Query
+        onlineUsersSubscriptionQuery = GetOnlineUsersSubscription.builder().build()
+
+        onlineUsersSubscription = Network.apolloClient.subscribe(onlineUsersSubscriptionQuery)
+
+        onlineUsersSubscription?.execute(object: ApolloSubscriptionCall.Callback<GetOnlineUsersSubscription.Data> {
+            override fun onFailure(e: ApolloException) {
+                Log.d("Online Users", e.localizedMessage)
+            }
+
+            override fun onResponse(response: Response<GetOnlineUsersSubscription.Data>) {
+                Log.d("Subs", response.data().toString())
+
+                val userList = mutableListOf(response.data()!!).flatMap {
+                        data -> data.online_users().map{
+                    data -> data.user()?.name()
+                    }
+                }
+
+                listItems = userList.toMutableList()
+
+                refreshListView(listItems)
+            }
+
+            override fun onConnected() {
+                Log.d("Online Users", "Connected to WS" )
+            }
+
+            override fun onTerminated() {
+                Log.d("Online Users", "Dis-connected from WS" )
+            }
+
+            override fun onCompleted() {
+            }
+
+        })
+    }

Now, we will update the UI with the results from this subscription. Update the onCreate with the subscribeOnlineUsers function invocation:

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     override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)

        // Subscribe to online users list
        subscribeOnlineUsers()
    }

We need to discard the web socket connection as soon as the fragment is not in view,

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   // Disable Subscriptions
    override fun onPause() {
        super.onPause()
        onlineUsersSubscription?.cancel()
        updateLastSeenTimer.cancel()
    }

Now that we have the real data, let's remove the mock online users in listItems variable

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private val listItems = arrayOf(
-        "SomeUser1",
-        "SomeUser2 ",
-        "SomeUser3",
-        "SomeUser4",
-        "SomeUser5",
-        "SomeUser6"
    )

How does this work?

We are using the apolloClient.subscribe which gives callback with onFailure, onResponse, onConnected, OnDisconnected and onCompleted methods to override. The response.data() object gives the result of the realtime data for the query we have made.

Re-run your android app and see yourself online! Don't be surprised; There could be other users online as well.

Awesome! You have completed implementations of a GraphQL Query, Mutation and Subscriptions.