Create Subscription and Render Result

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

Open src/screens/UsersScreen.js and add the following code, below the other imports

UserScreen.js

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import {useSubscription} from '@apollo/react-hooks';

Import gql from graphql-tag and define the subscription query:

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+ import gql from 'graphql-tag';


+ const SUBSCRIBE_TO_ONLINE_USERS = gql`
+   subscription {
+     online_users(order_by: {user: {name: asc}}) {
+       user {
+         name
+         id
+       }
+       id
+     }
+   }
+`; 

We are importing the useSubscription hook from @apollo/react-hooks and the graphql subscription query we defined above to fetch the online user data. The useSubscription hook behaves similar to the useQuery hook. It accepts the GraphQL subscription and returns data, error and loading information, except, data is realtime data.

Replace the component's body with this code.

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-   const data = {
-      "online_users": [
-        {
-          user: {
-            name: "User 1",
-            id: 1
-          },
-          id: 1
-        },
-        {
-          user: {
-            name: "User   2",
-            id: 2
-          },
-          id: 2
-        },
-      ]
-   }

+  const { data, error, loading } = useSubscription(SUBSCRIBE_TO_ONLINE_USERS)

+  if (loading) { return <CenterSpinner />}

+  if (error) {
+    return <Text> Error </Text>
+  }

  return (
    <View style={styles.container}>
      <ScrollView style={styles.scrollView} contentContainerStyle={styles.scrollViewContainer}>
      <FlatList
        data={data.online_users}
        renderItem={({item}) => <UserItem item={item} />}
        keyExtractor={(item) => item.user.name}
      />
      </ScrollView>
    </View>
  );

Refresh your 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.