React-Native scroll to top with Flatlist

Question

I'm having a lot of trouble scrolling to the top of my Flatlist so any help would be greatly appreciated!

Essentially it fetches the first 5 items from firebase, then when onEndReached is called we append the next 5 items to the list:

data: [...this.state.data, ...results]

For now I have a refresh button at the top of my view that does the following:

this.flatListRef.scrollToOffset({ animated: true, y: 0 });

If i click this when the first 5 items are rendered it scrolls to the top of the list as expected. The issue only occurs after the list has been appended to (I guess the items are off view?).

I have also tried 'ScrollToItem' however I'm guessing this doesn't work due to the following from React Native docs:

Note: Cannot scroll to locations outside the render window without specifying the getItemLayout prop.

Can anyone explain what is happening or know what I am doing wrong?

Thank you in advance!

getItemLayout: (not entirely sure what this does or how to work out length & offset etc)

getItemLayout = (data, index) => (
{ length: 50, offset: 50 * index, index }
)

return (
  <View>
    <FlatList
      ref={(ref) => { this.flatListRef = ref; }}
      onScroll={this.handleScroll}
      data={this.state.data}
      keyExtractor={item => item.key}
      ListFooterComponent={this.renderFooter()}
      onRefresh={this.handleRefresh}
      refreshing={this.state.newRefresh}
      onEndReached={this.handleEndRefresh}
      onEndReachedThreshold={0.05}
      getItemLayout={this.getItemLayout}
      renderItem={this.renderItem}
    />
    {this.state.refreshAvailable ? this.renderRefreshButton() : null}
  </View>
);

Answer 1

The correct syntax is

this.flatListRef.scrollToOffset({ animated: true, offset: 0 });

and you can also use

scrollToIndex