KeyboardAvoidingView.tsx

import * as React from 'react';
import {
  EmitterSubscription,
  Keyboard,
  KeyboardEvent,
  LayoutAnimation,
  Platform,
  Dimensions,
  ScreenRect,
} from 'react-native';
import { Box, BoxProps } from '../Box';

function subscribeToKeyboardEvents(
  onKeyboardChange: (e: KeyboardEvent) => void,
): { remove: () => void } {
  let subscriptions: EmitterSubscription[];
  if (Platform.OS === 'ios') {
    subscriptions = [
      Keyboard.addListener('keyboardWillChangeFrame', onKeyboardChange),
    ];
  } else {
    subscriptions = [
      Keyboard.addListener('keyboardDidHide', onKeyboardChange),
      Keyboard.addListener('keyboardDidShow', onKeyboardChange),
    ];
  }

  return {
    remove: () => {
      subscriptions.forEach((s) => s.remove());
    },
  };
}

/**
 * Manages the current value of the keyboard frame. This is useful in the
 * case the keyboard avoiding view is mounted while the keyboard is already
 * opened.
 */
class KeyboardManager {
  currentFrame: ScreenRect = {
    screenX: 0,
    screenY: Dimensions.get('window').height,
    width: 0,
    height: 0,
  };

  constructor() {
    subscribeToKeyboardEvents(this._handleKeyboardEvent);
  }

  _handleKeyboardEvent = (event: KeyboardEvent) => {
    this.currentFrame = event.endCoordinates;
  };
}

const globalKeyboardManager = new KeyboardManager();

function getVisibleHeight(endCoordinates: ScreenRect) {
  return Dimensions.get('window').height - endCoordinates.screenY;
}

type KeyboardAvoidingViewProps = BoxProps & {
  enabled?: boolean;
};

/**
 * Simpler and hopefully less buggy version of RN KeyboardAvoidingView.
 * To work better it must assume the view covers the bottom of the screen.
 */
export function KeyboardAvoidingView({
  enabled = true,
  ...others
}: KeyboardAvoidingViewProps) {
  const [bottom, setBottom] = React.useState(
    getVisibleHeight(globalKeyboardManager.currentFrame),
  );
  const lastBottomRef = React.useRef(bottom);
  lastBottomRef.current = bottom;

  React.useLayoutEffect(() => {
    const onKeyboardChange = (event: KeyboardEvent) => {
      const { duration, easing, endCoordinates } = event;
      const visibleHeight = getVisibleHeight(endCoordinates);
      if (lastBottomRef.current === visibleHeight) {
        return;
      }

      if (duration && easing) {
        LayoutAnimation.configureNext({
          duration: duration > 10 ? duration : 10,
          update: {
            duration: duration > 10 ? duration : 10,
            type: LayoutAnimation.Types[easing] || 'keyboard',
          },
        });
      }
      setBottom(visibleHeight);
    };

    const subscription = subscribeToKeyboardEvents(onKeyboardChange);
    return () => {
      subscription.remove();
    };
  }, []);

  // TODO: Either remove padding props or add padding to the bottom state.
  return <Box {...others} pb={`${enabled ? bottom : 0}px`} />;
}

@janicduplessis I wonder, what's in Box? 😛