[add] ScrollView support for pagingEnabled

Available in browsers that support CSS snappoints.

Fix #1057
Close #1212

Co-authored-by: Nicolas Gallagher <nicolasgallagher@gmail.com>

README.md

@@ -140,7 +140,7 @@ React Native v0.55
 | Picker                   | ✓      |  |
 | RefreshControl           | ✘      | Not started ([#1027](https://github.com/necolas/react-native-web/issues/1027)). |
 | SafeAreaView             | ✓      |  |
-| ScrollView               | ✓      | Missing momentum scroll events ([#1021](https://github.com/necolas/react-native-web/issues/1021)) and `pagingEnabled` ([#1057](https://github.com/necolas/react-native-web/issues/1057)). |
+| ScrollView               | ✓      | Missing momentum scroll events ([#1021](https://github.com/necolas/react-native-web/issues/1021)). |
 | SectionList              | ✓      |  |
 | Slider                   | ✘      | Not started ([#1022](https://github.com/necolas/react-native-web/issues/1022)). |
 | StatusBar                | (✓)    | Mock. No equivalent web APIs. |

packages/react-native-web/src/exports/ScrollView/__tests__/__snapshots__/index-test.js.snap

@@ -0,0 +1,7 @@
+// Jest Snapshot v1, https://goo.gl/fbAQLP
+
+exports[`components/ScrollView "pagingEnabled" prop 1`] = `undefined`;
+
+exports[`components/ScrollView "pagingEnabled" prop 2`] = `"y mandatory"`;
+
+exports[`components/ScrollView "pagingEnabled" prop 3`] = `"start"`;

packages/react-native-web/src/exports/ScrollView/__tests__/index-test.js

@@ -2,7 +2,8 @@
 
 import React from 'react';
 import ScrollView from '..';
-import { mount } from 'enzyme';
+import StyleSheet from '../../StyleSheet';
+import { mount, shallow } from 'enzyme';
 
 describe('components/ScrollView', () => {
   test('instance method setNativeProps', () => {
@@ -11,4 +12,17 @@ describe('components/ScrollView', () => {
       instance.setNativeProps();
     }).not.toThrow();
   });
+
+  test('"pagingEnabled" prop', () => {
+    const getStyleProp = (component, prop) => StyleSheet.flatten(component.prop('style'))[prop];
+
+    // false
+    const component = shallow(<ScrollView children={'Child'} />);
+    expect(getStyleProp(component, 'scrollSnapType')).toMatchSnapshot();
+
+    // true
+    component.setProps({ pagingEnabled: true });
+    expect(getStyleProp(component, 'scrollSnapType')).toMatchSnapshot();
+    expect(getStyleProp(component.children().childAt(0), 'scrollSnapAlign')).toMatchSnapshot();
+  });
 });

packages/react-native-web/src/exports/ScrollView/index.js

@@ -137,10 +137,10 @@ const ScrollView = createReactClass({
       onContentSizeChange,
       refreshControl,
       stickyHeaderIndices,
+      pagingEnabled,
       /* eslint-disable */
       keyboardDismissMode,
       onScroll,
-      pagingEnabled,
       /* eslint-enable */
       ...other
     } = this.props;
@@ -164,11 +164,24 @@ const ScrollView = createReactClass({
       };
     }
 
+    const hasStickyHeaderIndices = !horizontal && Array.isArray(stickyHeaderIndices);
     const children =
-      !horizontal && Array.isArray(stickyHeaderIndices)
+      hasStickyHeaderIndices || pagingEnabled
         ? React.Children.map(this.props.children, (child, i) => {
-            if (child && stickyHeaderIndices.indexOf(i) > -1) {
-              return <View style={styles.stickyHeader}>{child}</View>;
+            if (child != null) {
+              const isSticky = hasStickyHeaderIndices && stickyHeaderIndices.indexOf(i) > -1;
+              if (isSticky || pagingEnabled) {
+                return (
+                  <View
+                    style={StyleSheet.compose(
+                      isSticky && styles.stickyHeader,
+                      pagingEnabled && styles.pagingEnabledChild
+                    )}
+                  >
+                    {child}
+                  </View>
+                );
+              }
             } else {
               return child;
             }
@@ -181,15 +194,21 @@ const ScrollView = createReactClass({
         children={children}
         collapsable={false}
         ref={this._setInnerViewRef}
-        style={[horizontal && styles.contentContainerHorizontal, contentContainerStyle]}
+        style={StyleSheet.compose(
+          horizontal && styles.contentContainerHorizontal,
+          contentContainerStyle
+        )}
       />
     );
 
     const baseStyle = horizontal ? styles.baseHorizontal : styles.baseVertical;
+    const pagingEnabledStyle = horizontal
+      ? styles.pagingEnabledHorizontal
+      : styles.pagingEnabledVertical;
 
     const props = {
       ...other,
-      style: [baseStyle, this.props.style],
+      style: [baseStyle, pagingEnabled && pagingEnabledStyle, this.props.style],
       onTouchStart: this.scrollResponderHandleTouchStart,
       onTouchMove: this.scrollResponderHandleTouchMove,
       onTouchEnd: this.scrollResponderHandleTouchEnd,
@@ -223,7 +242,7 @@ const ScrollView = createReactClass({
     }
 
     return (
-      <ScrollViewClass {...props} ref={this._setScrollViewRef} style={props.style}>
+      <ScrollViewClass {...props} ref={this._setScrollViewRef}>
         {contentContainer}
       </ScrollViewClass>
     );
@@ -294,6 +313,15 @@ const styles = StyleSheet.create({
     position: 'sticky',
     top: 0,
     zIndex: 10
+  },
+  pagingEnabledHorizontal: {
+    scrollSnapType: 'x mandatory'
+  },
+  pagingEnabledVertical: {
+    scrollSnapType: 'y mandatory'
+  },
+  pagingEnabledChild: {
+    scrollSnapAlign: 'start'
   }
 });
 

packages/react-native-web/src/exports/View/ViewStylePropTypes.js

@@ -51,6 +51,8 @@ const ViewStylePropTypes = {
   overscrollBehavior: overscrollBehaviorType,
   overscrollBehaviorX: overscrollBehaviorType,
   overscrollBehaviorY: overscrollBehaviorType,
+  scrollSnapAlign: string,
+  scrollSnapType: string,
   WebkitMaskImage: string,
   WebkitOverflowScrolling: oneOf(['auto', 'touch'])
 };

packages/website/storybook/1-components/ScrollView/ScrollViewScreen.js

@@ -101,6 +101,12 @@ const ScrollViewScreen = () => (
         ]}
       />
 
+      <DocItem
+        name="pagingEnabled"
+        typeInfo="?boolean = false"
+        description="When true, the scroll view snaps to individual items in the list when scrolling."
+      />
+
       <DocItem
         name="scrollEnabled"
         typeInfo="?boolean = true"