Detect ScrollView has reached the end

I have a Text with long text inside a ScrollView and I want to detect when the user has scrolled to the end of the text so I can enable a button.

I've been debugging the event object from the onScroll event but there doesn't seem any value I can use.

Solution 1:

I did it like this:

import React from 'react';
import {ScrollView, Text} from 'react-native';
    
const isCloseToBottom = ({layoutMeasurement, contentOffset, contentSize}) => {
  const paddingToBottom = 20;
  return layoutMeasurement.height + contentOffset.y >=
    contentSize.height - paddingToBottom;
};
    
const MyCoolScrollViewComponent = ({enableSomeButton}) => (
  <ScrollView
    onScroll={({nativeEvent}) => {
      if (isCloseToBottom(nativeEvent)) {
        enableSomeButton();
      }
    }}
    scrollEventThrottle={400}
  >
    <Text>Here is very long lorem ipsum or something...</Text>
  </ScrollView>
);
    
export default MyCoolScrollViewComponent;

I wanted to add paddingToBottom because usually it is not needed that ScrollView is scrolled to the bottom till last pixel. But if you want that set paddingToBottom to zero.

Solution 2:

As people helped here I will add the simple code they write to make reached to top and reached to bottom event and I did a little illustration to make things simpler

<ScrollView
onScroll={({nativeEvent})=>{
if(isCloseToTop(nativeEvent)){
    //do something
}
if(isCloseToBottom(nativeEvent)){
   //do something
}
}}
>
...contents
</ScrollView>



isCloseToBottom({layoutMeasurement, contentOffset, contentSize}){
   return layoutMeasurement.height + contentOffset.y >= contentSize.height - 20;
}



ifCloseToTop({layoutMeasurement, contentOffset, contentSize}){
   return contentOffset.y == 0;
}

Solution 3:

<... onScroll={(e) => {
        let paddingToBottom = 10;
        paddingToBottom += e.nativeEvent.layoutMeasurement.height;
        if(e.nativeEvent.contentOffset.y >= e.nativeEvent.contentSize.height - paddingToBottom) {
          // make something...
        }
      }}>...

like this react-native 0.44