add a hide-on-scroll feature to ScrollView

Summary:
Add a stickyHeaderHiddenOnScroll option to keep the sticky header hidden during scrolling down, and only slide in when scrolling up
Changelog:
[General][Added] - Add a stickyHeaderHiddenOnScroll option to keep the sticky header hidden during scrolling down, and only slide in when scrolling up

Reviewed By: JoshuaGross

Differential Revision: D26900810

fbshipit-source-id: 6bfb1a4da07fff0763223d60836df187f9d95dd6

Author: Yan Zhang

Libraries/Components/ScrollView/ScrollView.js

@@ -589,6 +589,11 @@ export type Props = $ReadOnly<{|
    * The default value is true.
    */
   showsVerticalScrollIndicator?: ?boolean,
+  /**
+   * When true, Sticky header is hidden when scrolling down, and dock at the top
+   * when scrolling up
+   */
+  stickyHeaderHiddenOnScroll?: ?boolean,
   /**
    * An array of child indices determining which children get docked to the
    * top of the screen when scrolling. For example, passing
@@ -1642,6 +1647,7 @@ class ScrollView extends React.Component<Props, State> {
               onLayout={event => this._onStickyHeaderLayout(index, event, key)}
               scrollAnimatedValue={this._scrollAnimatedValue}
               inverted={this.props.invertStickyHeaders}
+              hiddenOnScroll={this.props.stickyHeaderHiddenOnScroll}
               scrollViewHeight={this.state.layoutHeight}>
               {child}
             </StickyHeaderComponent>

Libraries/Components/ScrollView/ScrollViewStickyHeader.js

@@ -9,6 +9,10 @@
  */
 
 import AnimatedImplementation from '../../Animated/AnimatedImplementation';
+import AnimatedAddition from '../../Animated/nodes/AnimatedAddition';
+import AnimatedDiffClamp from '../../Animated/nodes/AnimatedDiffClamp';
+import AnimatedNode from '../../Animated/nodes/AnimatedNode';
+
 import * as React from 'react';
 import StyleSheet from '../../StyleSheet/StyleSheet';
 import View from '../View/View';
@@ -29,6 +33,7 @@ export type Props = {
   // The height of the parent ScrollView. Currently only set when inverted.
   scrollViewHeight: ?number,
   nativeID?: ?string,
+  hiddenOnScroll?: ?boolean,
   ...
 };
 
@@ -50,7 +55,7 @@ class ScrollViewStickyHeader extends React.Component<Props, State> {
     translateY: null,
   };
 
-  _translateY: ?AnimatedImplementation.Interpolation = null;
+  _translateY: ?AnimatedNode = null;
   _shouldRecreateTranslateY: boolean = true;
   _haveReceivedInitialZeroTranslateY: boolean = true;
   _ref: any; // TODO T53738161: flow type this, and the whole file
@@ -87,12 +92,15 @@ class ScrollViewStickyHeader extends React.Component<Props, State> {
   updateTranslateListener(
     translateY: AnimatedImplementation.Interpolation,
     isFabric: boolean,
+    offset: AnimatedDiffClamp | null,
   ) {
     if (this._translateY != null && this._animatedValueListenerId != null) {
       this._translateY.removeListener(this._animatedValueListenerId);
     }
+    offset
+      ? (this._translateY = new AnimatedAddition(translateY, offset))
+      : (this._translateY = translateY);
 
-    this._translateY = translateY;
     this._shouldRecreateTranslateY = false;
 
     if (!isFabric) {
@@ -178,7 +186,6 @@ class ScrollViewStickyHeader extends React.Component<Props, State> {
       // eslint-disable-next-line dot-notation
       (this._ref && this._ref['_internalInstanceHandle']?.stateNode?.canonical)
     );
-
     // Initially and in the case of updated props or layout, we
     // recreate this interpolated value. Otherwise, we do not recreate
     // when there are state changes.
@@ -259,6 +266,22 @@ class ScrollViewStickyHeader extends React.Component<Props, State> {
           outputRange,
         }),
         isFabric,
+        this.props.hiddenOnScroll
+          ? new AnimatedDiffClamp(
+              this.props.scrollAnimatedValue
+                .interpolate({
+                  extrapolateLeft: 'clamp',
+                  inputRange: [layoutY, layoutY + 1],
+                  outputRange: ([0, 1]: Array<number>),
+                })
+                .interpolate({
+                  inputRange: [0, 1],
+                  outputRange: ([0, -1]: Array<number>),
+                }),
+              -this.state.layoutHeight,
+              0,
+            )
+          : null,
       );
     }