我在加载更多数据_fetchMoreData()的时候重新调用this._fetchData(),为什么这里会报‘this._fetchData() is not a function()’

componentDidMount(){
    this._fetchData(1)
}

//请求数据
_fetchData(page) {
    const that = this

    //如果页数不为零,则修改上滑isLoadingData的state为true;
    //否则就修改下拉刷新isRefreshing的state为true
    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="#ff0000"
                        title="Loading..."
                    />
                }
                onEndReached={this._fetchMoreData}
                onEndReachedThreshold={20}
                showsVerticalScrollIndicator={false}
                enableEmptySections={true}
            />
        </View>
    )
}