如何解决FlatList React native中的Key问题

Question

It my first experience with React, I have this problem in my program. Will you help me please? I use TMDB API in my application.

index.js:1 Warning: Encountered two children with the same key, `.$106242`. Keys should be unique so that components maintain their identity across updates. Non-unique keys may cause children to be duplicated and/or omitted — the behavior is unsupported and could change in a future version.
        in div (created by View)
        in View (created by ScrollView)
        in div (created by View)
        in View (created by ForwardRef)
        in ForwardRef (created by ScrollView)
        in ScrollView (created by VirtualizedList)
        in VirtualizedList (created by FlatList)
        in FlatList (at Search.js:71)
        in div (created by View)
        in View (at Search.js:65)
        in Search (at App.js:8)
        in App (created by ExpoRootComponent)
        in ExpoRootComponent (created by RootComponent)
        in RootComponent
        in div (created by View)
        in View (created by AppContainer)
        in div (created by View)
        in View (created by AppContainer)
        in AppContainer

<FlatList
  data={this.state.films}
  keyExtractor={(item, index) => item.id.toString()}
  renderItem={({ item }) => <Text> <FilmItem film={item} /> </Text>}
  onEndReachedThreshold={0.5}
  onEndReachedThreshold={0.5}
  onEndReached={() => {
    if (this.page < this.totalPages) { // On vérifie qu'on n'a pas atteint la fin de la pagination (totalPages) avant de charger plus d'éléments
      this._loadFilms()
    }
  }}
/>

Any proposition

Answer 1

Change you flatlist code to this,

<FlatList
    data = {this.state.films}
    keyExtractor = {(item, index) => index+"_"+item.id.toString() }
    renderItem={({item}) => <Text> <FilmItem film={item} /> </Text>}
    onEndReachedThreshold={0.5}
    onEndReachedThreshold={0.5}
    onEndReached={() => {
        if (this.page < this.totalPages) { // On vérifie qu'on n'a pas atteint la fin de la pagination (totalPages) avant de charger plus d'éléments
            this._loadFilms()
        }
    }}
/>

Answer 2

you can use index or combination of index and any property of films for keyExtractor. In below example I have used index and added comment on the same line which can also be used in place of index.

<FlatList
    data = {this.state.films}
    keyExtractor = {(item, index) => index } // `${item.id.toString()}-${index}`
    renderItem={({item}) => <Text> <FilmItem film={item} /> </Text>}
    onEndReachedThreshold={0.5}
    onEndReachedThreshold={0.5}
    onEndReached={() => {
        if (this.page < this.totalPages) { // On vérifie qu'on n'a pas atteint la fin de la pagination (totalPages) avant de charger plus d'éléments
            this._loadFilms()
        }
    }}
/>