react-native 滚到底部事件

let { contentOffset,contentSize,layoutMeasurement } = e.nativeEvent;
let [ offsetY,visibleH,contentH ]  = [ contentOffset.y,layoutMeasurement.height,contentSize.height ];
//距离底部40距离
 if (contentH - offsetY <= visibleH + 40 && this.lastContentHeight != contentH && this.state.currentSize < this.totalSize) {
        alert('success')
 }