How to set listener in the state?-CodePudding

I have a Firestore onSnapshot listener listening to changes on a document but I cant seem to understand how it works if I set it in the state like below:

constructor(props) {
 super(props);         
 this.fetchChatsListener = null;
}

and this is how I set it:

this.fetchChatsListener = firestore().collection('chats').doc(documentSnapshot.id).collection('messages').where('created', '>=', currenttime);
this.state.sent_message_id != '' ? this.fetchChatsListener.where(firebase.firestore.FieldPath.documentId(), '!=', this.state.sent_message_id) : ''
  this.fetchChatsListener.orderBy('created', 'desc')
    .onSnapshot({
      error: (e) => console.error(e),
      next: (querySnapshot_) => {

        querySnapshot_.docChanges().forEach(change => {
          this.state.dataSource.push({
            ...change.doc.data(),
            key: change.doc.id,
          });
        });

        this.setState({
          chatEntered: true,
          dataSource: this.state.dataSource,
          refreshingMessages: false,
          current_chat_id: documentSnapshot.id
        });

      },
    });

I call this function to unsubscribe from it:

unsubscribe_chats_listener() {
  this.fetchChatsListener;
  this.fetchChatsListener = null;
}

but unfortunately it does not unsubscribe because I keep receiving new changes.

UPDATE

when I try to unsubscribe using:

this.fetchChatsListener();

it fails with this error:

TypeError: this.fetchChatsListener is not a function

CodePudding user response：

The OP code only mentions the unsubscribe function, it needs to invoke it.

unsubscribe_chats_listener() {
  this.fetchChatsListener();  // note the parens, causing invocation
  this.fetchChatsListener = null;
}

EDIT

this.fetchChatsListener is being initialized to a query. Query's aren't unsubscribe functions.

this.fetchChatsListener = firestore().collection('chats') // a collection ref
.doc(documentSnapshot.id)  // a doc ref
.collection('messages')    // a collection ref
.where('created', '>=', currenttime);  // a query

onSnapshot() returns the unsubscribe function, so set the property there...

let query = firestore().collection('chats')
  .doc(documentSnapshot.id)
  .collection('messages')
  .where('created', '>=', currenttime);

  this.state.sent_message_id != '' ? query.fetchChatsListener.where(firebase.firestore.FieldPath.documentId(), '!=', this.state.sent_message_id) : ''
  
  query.orderBy('created', 'desc')
  this.fetchChatsListener = query.onSnapshot({  // an unsubscribe function
      error: (e) => console.error(e),
      next: (querySnapshot_) => {
      // ...