javascript - firebase child added action triggers multiple times when react navigation back button clicked -


i have weird problem. have component listing comments of specific movie. triggers firebase on(child_added) in componentwillmount. , when child added, add item reducer array. works perfect. codes that:

main component: 

class ... extends .... { render () { return () {  <comments ...props /> <comment /> // button pops modal when click  } } }

comments component: 

class comments extends component {  .....  componentwillmount() {         this.props.fetchmoviecomments(this.props.movie.id);     }  ......  render () { // listing array of comments. no problem in here }  }

fetchmoviecomments action:

export function fetchmoviecomments(id) {     console.log('tattaaaa');     const ref = firebase.database().ref(`comments/${id}`);     return (dispatch) => {         ref.on('child_added', (snapshot) => {             console.log('aaaaaa');             const commentdata = snapshot.val();             commentdata.uid = snapshot.key;                   const userref =                    firebase.database().ref(`users/${snapshot.val().userid}`);                   userref.once('value', (snap) => {                    console.log('bbbb');                 commentdata.name = snap.val().name;                 dispatch({ type: inject_movie_comment, payload: commentdata });             }).catch(err => console.log(err));             dispatch({ type: fetch_movie_comments, payload: snapshot.val() });         });         ref.on('child_removed', (snapshot) => {             const removedid = snapshot.key;             dispatch({ type: remove_comment, payload: removedid });         });     }; }

when child added triggered, fetch username of comment in it. there no problem here also.

for example, searched movie , lot of movies listed. choose 1 of them, , commented movie. there no problem comment appears in list, when click button (react navigation) , go movie again , add comment, adds comment twice. not database. adds firebase database 1 time child_added listener triggers 2 times. logs console 2 times: 'aaaaaa' , adds last added child array 2 times.

guess what? if make 5 times , forward, , comment, last comment appears 5 times. lol. added database 1 time, child_added triggers 5 times.

as said, used react navigation. how can solve problem? make wrong choice trigger fetching comments in componentwillmount?


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