This._fetchData (page) is not a function?

I re-call this._fetchData () when I load more data _ fetchMoreData () . Why do I report "this._fetchData () is not a function ()"

here?
componentDidMount(){
    this._fetchData(1)
}

//
_fetchData(page) {
    const that = this

    //,isLoadingDatastatetrue;
    //isRefreshingstatetrue
    if(page !== 0){
        this.setState({
            isLoadingData: true
        })
    }else{
        this.setState({
            isRefreshing: true
        })
    } 
    try {
        //request.get("http://www.rapapi.org/mockjs/33254/api/list?accessToken=labike&page=10")
        request.get(Config.api.baseUrl + Config.api.list, {
            accessToken: "labike",
            page: page
        }) 
}

_fetchMoreData(){
    // if(!this._hasMoreData || this.state.isLoadingData){
    //     return
    // }
    const page = cacleResult.nextPage
    console.log(page)
    this._fetchData(page)
}

render(){
    return(
        <View style={styles.container}>
            <View style={styles.header}>
                <Text style={styles.headerTitle}>Header</Text>
            </View>
            <ListView
                dataSource={this.state.dataSource}
                renderRow={this._renderItem}
                renderFooter={this._renderFooter}
                refreshControl={
                    <RefreshControl
                        refreshing={this.state.isRefreshing}
                        onRefresh={this._onRefresh}
                        tintColor="-sharpff0000"
                        title="Loading..."
                    />
                }
                onEndReached={this._fetchMoreData}
                onEndReachedThreshold={20}
                showsVerticalScrollIndicator={false}
                enableEmptySections={true}
            />
        </View>
    )
}
Mar.03,2021

this scope problem, change _ fetchMoreData to arrow function

MySQL Query : SELECT * FROM `codeshelper`.`v9_news` WHERE status=99 AND catid='6' ORDER BY rand() LIMIT 5
MySQL Error : Disk full (/tmp/#sql-temptable-64f5-1bf1ba3-3a14a.MAI); waiting for someone to free some space... (errno: 28 "No space left on device")
MySQL Errno : 1021
Message : Disk full (/tmp/#sql-temptable-64f5-1bf1ba3-3a14a.MAI); waiting for someone to free some space... (errno: 28 "No space left on device")
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