ReactNative: 使用滚动视图ScrollView组件

一、简介

当页面内容的非常多时，即使换行后仍然无法充分显示，此时最好的解决办法就是让页面可以滚动显示。在React-Native中，提供了可供滚动的视图组件ScrollView组件。它的属性和方法以及使用基本和iOS的UIScrollView类似，下面简单列举常见的属性和函数，更多的详细请查看API即可。详细API如下：

/**
 * Copyright (c) 2015-present, Facebook, Inc.
 * All rights reserved.
 *
 * This source code is licensed under the BSD-style license found in the
 * LICENSE file in the root directory of this source tree. An additional grant
 * of patent rights can be found in the PATENTS file in the same directory.
 *
 * @providesModule ScrollView
 * @flow
 */
'use strict';

const Animated = require('Animated');
const ColorPropType = require('ColorPropType');
const EdgeInsetsPropType = require('EdgeInsetsPropType');
const Platform = require('Platform');
const PointPropType = require('PointPropType');
const React = require('React');
const ReactNative = require('ReactNative');
const ScrollResponder = require('ScrollResponder');
const ScrollViewStickyHeader = require('ScrollViewStickyHeader');
const StyleSheet = require('StyleSheet');
const StyleSheetPropType = require('StyleSheetPropType');
const View = require('View');
const ViewPropTypes = require('ViewPropTypes');
const ViewStylePropTypes = require('ViewStylePropTypes');

const dismissKeyboard = require('dismissKeyboard');
const flattenStyle = require('flattenStyle');
const invariant = require('fbjs/lib/invariant');
const processDecelerationRate = require('processDecelerationRate');
const PropTypes = React.PropTypes;
const requireNativeComponent = require('requireNativeComponent');

/**
 * Component that wraps platform ScrollView while providing
 * integration with touch locking "responder" system.
 *
 * Keep in mind that ScrollViews must have a bounded height in order to work,
 * since they contain unbounded-height children into a bounded container (via
 * a scroll interaction). In order to bound the height of a ScrollView, either
 * set the height of the view directly (discouraged) or make sure all parent
 * views have bounded height. Forgetting to transfer `{flex: 1}` down the
 * view stack can lead to errors here, which the element inspector makes
 * easy to debug.
 *
 * Doesn't yet support other contained responders from blocking this scroll
 * view from becoming the responder.
 *
 *
 * `<ScrollView>` vs [`<FlatList>`](/react-native/docs/flatlist.html) - which one to use?
 *
 * `ScrollView` simply renders all its react child components at once. That
 * makes it very easy to understand and use.
 *
 * On the other hand, this has a performance downside. Imagine you have a very
 * long list of items you want to display, maybe several screens worth of
 * content. Creating JS components and native views for everythign all at once,
 * much of which may not even be shown, will contribute to slow rendering and
 * increased memory usage.
 *
 * This is where `FlatList` comes into play. `FlatList` renders items lazily,
 * just when they are about to appear, and removes items that scroll way off
 * screen to save memory and processing time.
 *
 * `FlatList` is also handy if you want to render separators between your items,
 * multiple columns, infinite scroll loading, or any number of other features it
 * supports out of the box.
 */
// $FlowFixMe(>=0.41.0)
const ScrollView = React.createClass({
  propTypes: {
    ...ViewPropTypes,
    /**
     * Controls whether iOS should automatically adjust the content inset
     * for scroll views that are placed behind a navigation bar or
     * tab bar/ toolbar. The default value is true.
     * @platform ios
     */
    automaticallyAdjustContentInsets: PropTypes.bool,
    /**
     * The amount by which the scroll view content is inset from the edges
     * of the scroll view. Defaults to `{top: 0, left: 0, bottom: 0, right: 0}`.
     * @platform ios
     */
    contentInset: EdgeInsetsPropType,
    /**
     * Used to manually set the starting scroll offset.
     * The default value is `{x: 0, y: 0}`.
     * @platform ios
     */
    contentOffset: PointPropType,
    /**
     * When true, the scroll view bounces when it reaches the end of the
     * content if the content is larger then the scroll view along the axis of
     * the scroll direction. When false, it disables all bouncing even if
     * the `alwaysBounce*` props are true. The default value is true.
     * @platform ios
     */
    bounces: PropTypes.bool,
    /**
     * When true, gestures can drive zoom past min/max and the zoom will animate
     * to the min/max value at gesture end, otherwise the zoom will not exceed
     * the limits.
     * @platform ios
     */
    bouncesZoom: PropTypes.bool,
    /**
     * When true, the scroll view bounces horizontally when it reaches the end
     * even if the content is smaller than the scroll view itself. The default
     * value is true when `horizontal={true}` and false otherwise.
     * @platform ios
     */
    alwaysBounceHorizontal: PropTypes.bool,
    /**
     * When true, the scroll view bounces vertically when it reaches the end
     * even if the content is smaller than the scroll view itself. The default
     * value is false when `horizontal={true}` and true otherwise.
     * @platform ios
     */
    alwaysBounceVertical: PropTypes.bool,
    /**
     * When true, the scroll view automatically centers the content when the
     * content is smaller than the scroll view bounds; when the content is
     * larger than the scroll view, this property has no effect. The default
     * value is false.
     * @platform ios
     */
    centerContent: PropTypes.bool,
    /**
     * These styles will be applied to the scroll view content container which
     * wraps all of the child views. Example:
     *
     *   return (
     *     <ScrollView contentContainerStyle={styles.contentContainer}>
     *     </ScrollView>
     *   );
     *   ...
     *   const styles = StyleSheet.create({
     *     contentContainer: {
     *       paddingVertical: 20
     *     }
     *   });
     */
    contentContainerStyle: StyleSheetPropType(ViewStylePropTypes),
    /**
     * A floating-point number that determines how quickly the scroll view
     * decelerates after the user lifts their finger. You may also use string
     * shortcuts `"normal"` and `"fast"` which match the underlying iOS settings
     * for `UIScrollViewDecelerationRateNormal` and
     * `UIScrollViewDecelerationRateFast` respectively.
     *   - normal: 0.998 (the default)
     *   - fast: 0.99
     * @platform ios
     */
    decelerationRate: PropTypes.oneOfType([
      PropTypes.oneOf(['fast', 'normal']),
      PropTypes.number,
    ]),
    /**
     * When true, the scroll view's children are arranged horizontally in a row
     * instead of vertically in a column. The default value is false.
     */
    horizontal: PropTypes.bool,
    /**
     * The style of the scroll indicators.
     *   - `default` (the default), same as `black`.
     *   - `black`, scroll indicator is black. This style is good against a light background.
     *   - `white`, scroll indicator is white. This style is good against a dark background.
     * @platform ios
     */
    indicatorStyle: PropTypes.oneOf([
      'default', // default
      'black',
      'white',
    ]),
    /**
     * When true, the ScrollView will try to lock to only vertical or horizontal
     * scrolling while dragging.  The default value is false.
     * @platform ios
     */
    directionalLockEnabled: PropTypes.bool,
    /**
     * When false, once tracking starts, won't try to drag if the touch moves.
     * The default value is true.
     * @platform ios
     */
    canCancelContentTouches: PropTypes.bool,
    /**
     * Determines whether the keyboard gets dismissed in response to a drag.
     *   - 'none' (the default), drags do not dismiss the keyboard.
     *   - 'on-drag', the keyboard is dismissed when a drag begins.
     *   - 'interactive', the keyboard is dismissed interactively with the drag and moves in
     *     synchrony with the touch; dragging upwards cancels the dismissal.
     *     On android this is not supported and it will have the same behavior as 'none'.
     */
    keyboardDismissMode: PropTypes.oneOf([
      'none', // default
      'interactive',
      'on-drag',
    ]),
    /**
     * Determines when the keyboard should stay visible after a tap.
     *
     *   - 'never' (the default), tapping outside of the focused text input when the keyboard
     *     is up dismisses the keyboard. When this happens, children won't receive the tap.
     *   - 'always', the keyboard will not dismiss automatically, and the scroll view will not
     *     catch taps, but children of the scroll view can catch taps.
     *   - 'handled', the keyboard will not dismiss automatically when the tap was handled by
     *     a children, (or captured by an ancestor).
     *   - false, deprecated, use 'never' instead
     *   - true, deprecated, use 'always' instead
     */
    keyboardShouldPersistTaps: PropTypes.oneOf(['always', 'never', 'handled', false, true]),
    /**
     * The maximum allowed zoom scale. The default value is 1.0.
     * @platform ios
     */
    maximumZoomScale: PropTypes.number,
    /**
     * The minimum allowed zoom scale. The default value is 1.0.
     * @platform ios
     */
    minimumZoomScale: PropTypes.number,
    /**
     * Fires at most once per frame during scrolling. The frequency of the
     * events can be controlled using the `scrollEventThrottle` prop.
     */
    onScroll: PropTypes.func,
    /**
     * Called when a scrolling animation ends.
     * @platform ios
     */
    onScrollAnimationEnd: PropTypes.func,
    /**
     * Called when scrollable content view of the ScrollView changes.
     *
     * Handler function is passed the content width and content height as parameters:
     * `(contentWidth, contentHeight)`
     *
     * It's implemented using onLayout handler attached to the content container
     * which this ScrollView renders.
     */
    onContentSizeChange: PropTypes.func,
    /**
     * When true, the scroll view stops on multiples of the scroll view's size
     * when scrolling. This can be used for horizontal pagination. The default
     * value is false.
     */
    pagingEnabled: PropTypes.bool,
    /**
     * When false, the content does not scroll.
     * The default value is true.
     */
    scrollEnabled: PropTypes.bool,
    /**
     * This controls how often the scroll event will be fired while scrolling
     * (as a time interval in ms). A lower number yields better accuracy for code
     * that is tracking the scroll position, but can lead to scroll performance
     * problems due to the volume of information being send over the bridge.
     * You will not notice a difference between values set between 1-16 as the
     * JS run loop is synced to the screen refresh rate. If you do not need precise
     * scroll position tracking, set this value higher to limit the information
     * being sent across the bridge. The default value is zero, which results in
     * the scroll event being sent only once each time the view is scrolled.
     * @platform ios
     */
    scrollEventThrottle: PropTypes.number,
    /**
     * The amount by which the scroll view indicators are inset from the edges
     * of the scroll view. This should normally be set to the same value as
     * the `contentInset`. Defaults to `{0, 0, 0, 0}`.
     * @platform ios
     */
    scrollIndicatorInsets: EdgeInsetsPropType,
    /**
     * When true, the scroll view scrolls to top when the status bar is tapped.
     * The default value is true.
     * @platform ios
     */
    scrollsToTop: PropTypes.bool,
    /**
     * When true, shows a horizontal scroll indicator.
     * The default value is true.
     */
    showsHorizontalScrollIndicator: PropTypes.bool,
    /**
     * When true, shows a vertical scroll indicator.
     * The default value is true.
     */
    showsVerticalScrollIndicator: PropTypes.bool,
    /**
     * An array of child indices determining which children get docked to the
     * top of the screen when scrolling. For example, passing
     * `stickyHeaderIndices={[0]}` will cause the first child to be fixed to the
     * top of the scroll view. This property is not supported in conjunction
     * with `horizontal={true}`.
     */
    stickyHeaderIndices: PropTypes.arrayOf(PropTypes.number),
    style: StyleSheetPropType(ViewStylePropTypes),
    /**
     * When set, causes the scroll view to stop at multiples of the value of
     * `snapToInterval`. This can be used for paginating through children
     * that have lengths smaller than the scroll view. Used in combination
     * with `snapToAlignment`.
     * @platform ios
     */
    snapToInterval: PropTypes.number,
    /**
     * When `snapToInterval` is set, `snapToAlignment` will define the relationship
     * of the snapping to the scroll view.
     *   - `start` (the default) will align the snap at the left (horizontal) or top (vertical)
     *   - `center` will align the snap in the center
     *   - `end` will align the snap at the right (horizontal) or bottom (vertical)
     * @platform ios
     */
    snapToAlignment: PropTypes.oneOf([
      'start', // default
      'center',
      'end',
    ]),
    /**
     * Experimental: When true, offscreen child views (whose `overflow` value is
     * `hidden`) are removed from their native backing superview when offscreen.
     * This can improve scrolling performance on long lists. The default value is
     * true.
     */
    removeClippedSubviews: PropTypes.bool,
    /**
     * The current scale of the scroll view content. The default value is 1.0.
     * @platform ios
     */
    zoomScale: PropTypes.number,

    /**
     * A RefreshControl component, used to provide pull-to-refresh
     * functionality for the ScrollView. Only works for vertical ScrollViews
     * (`horizontal` prop must be `false`).
     *
     * See [RefreshControl](docs/refreshcontrol.html).
     */
    refreshControl: PropTypes.element,

    /**
     * Sometimes a scrollview takes up more space than its content fills. When this is
     * the case, this prop will fill the rest of the scrollview with a color to avoid setting
     * a background and creating unnecessary overdraw. This is an advanced optimization
     * that is not needed in the general case.
     * @platform android
     */
    endFillColor: ColorPropType,

    /**
     * Tag used to log scroll performance on this scroll view. Will force
     * momentum events to be turned on (see sendMomentumEvents). This doesn't do
     * anything out of the box and you need to implement a custom native
     * FpsListener for it to be useful.
     * @platform android
     */
    scrollPerfTag: PropTypes.string,

     /**
     * Used to override default value of overScroll mode.
     *
     * Possible values:
     *
     *  - `'auto'` - Default value, allow a user to over-scroll
     *    this view only if the content is large enough to meaningfully scroll.
     *  - `'always'` - Always allow a user to over-scroll this view.
     *  - `'never'` - Never allow a user to over-scroll this view.
     *
     * @platform android
     */
    overScrollMode: PropTypes.oneOf([
      'auto',
      'always',
      'never',
    ]),
  },

  mixins: [ScrollResponder.Mixin],

  _scrollAnimatedValue: (new Animated.Value(): Animated.Value),
  _scrollAnimatedValueAttachment: (null: ?{detach: () => void}),
  _stickyHeaderRefs: (new Map(): Map<number, ScrollViewStickyHeader>),
  _headerLayoutYs: (new Map(): Map<string, number>),
  getInitialState: function() {
    return this.scrollResponderMixinGetInitialState();
  },

  componentWillMount: function() {
    this._scrollAnimatedValue = new Animated.Value();
    this._stickyHeaderRefs = new Map();
    this._headerLayoutYs = new Map();
  },

  componentDidMount: function() {
    this._updateAnimatedNodeAttachment();
  },

  componentDidUpdate: function() {
    this._updateAnimatedNodeAttachment();
  },

  componentWillUnmount: function() {
    if (this._scrollAnimatedValueAttachment) {
      this._scrollAnimatedValueAttachment.detach();
    }
  },

  setNativeProps: function(props: Object) {
    this._scrollViewRef && this._scrollViewRef.setNativeProps(props);
  },

  /**
   * Returns a reference to the underlying scroll responder, which supports
   * operations like `scrollTo`. All ScrollView-like components should
   * implement this method so that they can be composed while providing access
   * to the underlying scroll responder's methods.
   */
  getScrollResponder: function(): ScrollView {
    return this;
  },

  getScrollableNode: function(): any {
    return ReactNative.findNodeHandle(this._scrollViewRef);
  },

  getInnerViewNode: function(): any {
    return ReactNative.findNodeHandle(this._innerViewRef);
  },

  /**
   * Scrolls to a given x, y offset, either immediately or with a smooth animation.
   *
   * Example:
   *
   * `scrollTo({x: 0; y: 0; animated: true})`
   *
   * Note: The weird function signature is due to the fact that, for historical reasons,
   * the function also accepts separate arguments as an alternative to the options object.
   * This is deprecated due to ambiguity (y before x), and SHOULD NOT BE USED.
   */
  scrollTo: function(
    y?: number | { x?: number, y?: number, animated?: boolean },
    x?: number,
    animated?: boolean
  ) {
    if (typeof y === 'number') {
      console.warn('`scrollTo(y, x, animated)` is deprecated. Use `scrollTo({x: 5, y: 5, ' +
        'animated: true})` instead.');
    } else {
      ({x, y, animated} = y || {});
    }
    this.getScrollResponder().scrollResponderScrollTo(
      {x: x || , y: y || , animated: animated !== false}
    );
  },

  /**
   * If this is a vertical ScrollView scrolls to the bottom.
   * If this is a horizontal ScrollView scrolls to the right.
   *
   * Use `scrollToEnd({animated: true})` for smooth animated scrolling,
   * `scrollToEnd({animated: false})` for immediate scrolling.
   * If no options are passed, `animated` defaults to true.
   */
  scrollToEnd: function(
    options?: { animated?: boolean },
  ) {
    // Default to true
    const animated = (options && options.animated) !== false;
    this.getScrollResponder().scrollResponderScrollToEnd({
      animated: animated,
    });
  },

  /**
   * Deprecated, use `scrollTo` instead.
   */
  scrollWithoutAnimationTo: function(y: number = , x: number = ) {
    console.warn('`scrollWithoutAnimationTo` is deprecated. Use `scrollTo` instead');
    this.scrollTo({x, y, animated: false});
  },

  _getKeyForIndex: function(index, childArray) {
    const child = childArray[index];
    return child && child.key;
  },

  _updateAnimatedNodeAttachment: function() {
    if (this.props.stickyHeaderIndices && this.props.stickyHeaderIndices.length > ) {
      if (!this._scrollAnimatedValueAttachment) {
        this._scrollAnimatedValueAttachment = Animated.attachNativeEvent(
          this._scrollViewRef,
          'onScroll',
          [{nativeEvent: {contentOffset: {y: this._scrollAnimatedValue}}}]
        );
      }
    } else {
      if (this._scrollAnimatedValueAttachment) {
        this._scrollAnimatedValueAttachment.detach();
      }
    }
  },

  _setStickyHeaderRef: function(key, ref) {
    if (ref) {
      this._stickyHeaderRefs.set(key, ref);
    } else {
      this._stickyHeaderRefs.delete(key);
    }
  },

  _onStickyHeaderLayout: function(index, event, key) {
    if (!this.props.stickyHeaderIndices) {
      return;
    }
    const childArray = React.Children.toArray(this.props.children);
    if (key !== this._getKeyForIndex(index, childArray)) {
      // ignore stale layout update
      return;
    }

    const layoutY = event.nativeEvent.layout.y;
    this._headerLayoutYs.set(key, layoutY);

    const indexOfIndex = this.props.stickyHeaderIndices.indexOf(index);
    const previousHeaderIndex = this.props.stickyHeaderIndices[indexOfIndex - ];
    if (previousHeaderIndex != null) {
      const previousHeader = this._stickyHeaderRefs.get(
        this._getKeyForIndex(previousHeaderIndex, childArray)
      );
      previousHeader && previousHeader.setNextHeaderY(layoutY);
    }
  },

  _handleScroll: function(e: Object) {
    if (__DEV__) {
      if (this.props.onScroll && this.props.scrollEventThrottle == null && Platform.OS === 'ios') {
        console.log( // eslint-disable-line no-console-disallow
          'You specified `onScroll` on a <ScrollView> but not ' +
          '`scrollEventThrottle`. You will only receive one event. ' +
          'Using `16` you get all the events but be aware that it may ' +
          'cause frame drops, use a bigger number if you don\'t need as ' +
          'much precision.'
        );
      }
    }
    if (Platform.OS === 'android') {
      if (this.props.keyboardDismissMode === 'on-drag') {
        dismissKeyboard();
      }
    }
    this.scrollResponderHandleScroll(e);
  },

  _handleContentOnLayout: function(e: Object) {
    const {width, height} = e.nativeEvent.layout;
    this.props.onContentSizeChange && this.props.onContentSizeChange(width, height);
  },

  _scrollViewRef: (null: ?ScrollView),
  _setScrollViewRef: function(ref: ?ScrollView) {
    this._scrollViewRef = ref;
  },

  _innerViewRef: (null: ?View),
  _setInnerViewRef: function(ref: ?View) {
    this._innerViewRef = ref;
  },

  render: function() {
    let ScrollViewClass;
    let ScrollContentContainerViewClass;
    if (Platform.OS === 'ios') {
      ScrollViewClass = RCTScrollView;
      ScrollContentContainerViewClass = RCTScrollContentView;
    } else if (Platform.OS === 'android') {
      if (this.props.horizontal) {
        ScrollViewClass = AndroidHorizontalScrollView;
      } else {
        ScrollViewClass = AndroidScrollView;
      }
      ScrollContentContainerViewClass = View;
    }

    invariant(
      ScrollViewClass !== undefined,
      'ScrollViewClass must not be undefined'
    );

    invariant(
      ScrollContentContainerViewClass !== undefined,
      'ScrollContentContainerViewClass must not be undefined'
    );

    const contentContainerStyle = [
      this.props.horizontal && styles.contentContainerHorizontal,
      this.props.contentContainerStyle,
    ];
    let style, childLayoutProps;
    if (__DEV__ && this.props.style) {
      style = flattenStyle(this.props.style);
      childLayoutProps = ['alignItems', 'justifyContent']
        .filter((prop) => style && style[prop] !== undefined);
      invariant(
        childLayoutProps.length === ,
        'ScrollView child layout (' + JSON.stringify(childLayoutProps) +
          ') must be applied through the contentContainerStyle prop.'
      );
    }

    let contentSizeChangeProps = {};
    if (this.props.onContentSizeChange) {
      contentSizeChangeProps = {
        onLayout: this._handleContentOnLayout,
      };
    }

    const {stickyHeaderIndices} = this.props;
    const hasStickyHeaders = stickyHeaderIndices && stickyHeaderIndices.length > ;
    const childArray = hasStickyHeaders && React.Children.toArray(this.props.children);
    const children = hasStickyHeaders ?
      childArray.map((child, index) => {
        const indexOfIndex = child ? stickyHeaderIndices.indexOf(index) : -;
        if (indexOfIndex > -) {
          const key = child.key;
          const nextIndex = stickyHeaderIndices[indexOfIndex + ];
          return (
            <ScrollViewStickyHeader
              key={key}
              ref={(ref) => this._setStickyHeaderRef(key, ref)}
              nextHeaderLayoutY={
                this._headerLayoutYs.get(this._getKeyForIndex(nextIndex, childArray))
              }
              onLayout={(event) => this._onStickyHeaderLayout(index, event, key)}
              scrollAnimatedValue={this._scrollAnimatedValue}>
              {child}
            </ScrollViewStickyHeader>
          );
        } else {
          return child;
        }
      }) :
      this.props.children;
    const contentContainer =
      <ScrollContentContainerViewClass
        {...contentSizeChangeProps}
        ref={this._setInnerViewRef}
        style={contentContainerStyle}
        removeClippedSubviews={
          hasStickyHeaders && Platform.OS === 'android' ? false : this.props.removeClippedSubviews
        }
        collapsable={false}>
        {children}
      </ScrollContentContainerViewClass>;

    const alwaysBounceHorizontal =
      this.props.alwaysBounceHorizontal !== undefined ?
        this.props.alwaysBounceHorizontal :
        this.props.horizontal;

    const alwaysBounceVertical =
      this.props.alwaysBounceVertical !== undefined ?
        this.props.alwaysBounceVertical :
        !this.props.horizontal;

    const baseStyle = this.props.horizontal ? styles.baseHorizontal : styles.baseVertical;
    const props = {
      ...this.props,
      alwaysBounceHorizontal,
      alwaysBounceVertical,
      style: ([baseStyle, this.props.style]: ?Array<any>),
      // Override the onContentSizeChange from props, since this event can
      // bubble up from TextInputs
      onContentSizeChange: null,
      onMomentumScrollBegin: this.scrollResponderHandleMomentumScrollBegin,
      onMomentumScrollEnd: this.scrollResponderHandleMomentumScrollEnd,
      onResponderGrant: this.scrollResponderHandleResponderGrant,
      onResponderReject: this.scrollResponderHandleResponderReject,
      onResponderRelease: this.scrollResponderHandleResponderRelease,
      onResponderTerminate: this.scrollResponderHandleTerminate,
      onResponderTerminationRequest: this.scrollResponderHandleTerminationRequest,
      onScroll: this._handleScroll,
      onScrollBeginDrag: this.scrollResponderHandleScrollBeginDrag,
      onScrollEndDrag: this.scrollResponderHandleScrollEndDrag,
      onScrollShouldSetResponder: this.scrollResponderHandleScrollShouldSetResponder,
      onStartShouldSetResponder: this.scrollResponderHandleStartShouldSetResponder,
      onStartShouldSetResponderCapture: this.scrollResponderHandleStartShouldSetResponderCapture,
      onTouchEnd: this.scrollResponderHandleTouchEnd,
      onTouchMove: this.scrollResponderHandleTouchMove,
      onTouchStart: this.scrollResponderHandleTouchStart,
      scrollEventThrottle: hasStickyHeaders ?  : this.props.scrollEventThrottle,
      sendMomentumEvents: (this.props.onMomentumScrollBegin || this.props.onMomentumScrollEnd) ?
        true : false,
    };

    const { decelerationRate } = this.props;
    if (decelerationRate) {
      props.decelerationRate = processDecelerationRate(decelerationRate);
    }

    const refreshControl = this.props.refreshControl;

    if (refreshControl) {
      if (Platform.OS === 'ios') {
        // On iOS the RefreshControl is a child of the ScrollView.
        // tvOS lacks native support for RefreshControl, so don't include it in that case
        return (
          <ScrollViewClass {...props} ref={this._setScrollViewRef}>
            {Platform.isTVOS ? null : refreshControl}
            {contentContainer}
          </ScrollViewClass>
        );
      } else if (Platform.OS === 'android') {
        // On Android wrap the ScrollView with a AndroidSwipeRefreshLayout.
        // Since the ScrollView is wrapped add the style props to the
        // AndroidSwipeRefreshLayout and use flex: 1 for the ScrollView.
        // Note: we should only apply props.style on the wrapper
        // however, the ScrollView still needs the baseStyle to be scrollable

        return React.cloneElement(
          refreshControl,
          {style: props.style},
          <ScrollViewClass {...props} style={baseStyle} ref={this._setScrollViewRef}>
            {contentContainer}
          </ScrollViewClass>
        );
      }
    }
    return (
      <ScrollViewClass {...props} ref={this._setScrollViewRef}>
        {contentContainer}
      </ScrollViewClass>
    );
  }
});

const styles = StyleSheet.create({
  baseVertical: {
    flexGrow: ,
    flexShrink: ,
    flexDirection: 'column',
    overflow: 'scroll',
  },
  baseHorizontal: {
    flexGrow: ,
    flexShrink: ,
    flexDirection: 'row',
    overflow: 'scroll',
  },
  contentContainerHorizontal: {
    flexDirection: 'row',
  },
});

let nativeOnlyProps,
  AndroidScrollView,
  AndroidHorizontalScrollView,
  RCTScrollView,
  RCTScrollContentView;
if (Platform.OS === 'android') {
  nativeOnlyProps = {
    nativeOnly: {
      sendMomentumEvents: true,
    }
  };
  AndroidScrollView = requireNativeComponent(
    'RCTScrollView',
    (ScrollView: ReactClass<any>),
    nativeOnlyProps
  );
  AndroidHorizontalScrollView = requireNativeComponent(
    'AndroidHorizontalScrollView',
    (ScrollView: ReactClass<any>),
    nativeOnlyProps
  );
} else if (Platform.OS === 'ios') {
  nativeOnlyProps = {
    nativeOnly: {
      onMomentumScrollBegin: true,
      onMomentumScrollEnd : true,
      onScrollBeginDrag: true,
      onScrollEndDrag: true,
    }
  };
  RCTScrollView = requireNativeComponent(
    'RCTScrollView',
    (ScrollView: ReactClass<any>),
    nativeOnlyProps,
  );
  RCTScrollContentView = requireNativeComponent('RCTScrollContentView', View);
}

module.exports = ScrollView;

二、主要属性

//自动调节内容偏移
automaticallyAdjustContentInsets: PropTypes.bool,

//内容边距偏移
contentInset: EdgeInsetsPropType,

//指定刷新组件
refreshControl: element

//内容中心偏移
contentOffset: PointPropType,

//是否支持弹性
bounces: PropTypes.bool,

//描述在缩放超过缩放比例时,是否bounce,默认值为YES
bouncesZoom: PropTypes.bool,

//水平方向是否支持弹性
alwaysBounceHorizontal: PropTypes.bool,

//垂直方向是否支持弹性
alwaysBounceVertical: PropTypes.bool,

//内容是否居中
centerContent: PropTypes.bool,

//给内容视图创建StyleSheet样式
contentContainerStyle: StyleSheetPropType(ViewStylePropTypes),

//滚动速率
decelerationRate: PropTypes.oneOfType([
      PropTypes.oneOf(['fast', 'normal']),
      PropTypes.number,
]),

//子控件是否水平排列，也即滚动方式是否为水平方向，默认为垂直方向
horizontal: PropTypes.bool,

//滑动指示器样式
indicatorStyle: PropTypes.oneOf([
      'default', // default
      'black',
      'white',
]),

//是否限制只能在一个方向上滚动
directionalLockEnabled: PropTypes.bool,

//是否取消内容区域点击
canCancelContentTouches: PropTypes.bool,

//键盘消失模式
keyboardDismissMode: PropTypes.oneOf([
      'none', // default
      'interactive',
      'on-drag',
]),

//最大和最小缩放比率
maximumZoomScale: PropTypes.number,
minimumZoomScale: PropTypes.number,

//是否支持分页
pagingEnabled: PropTypes.bool,

//是否支持滚动
scrollEnabled: PropTypes.bool,

//滚动指示器偏移
scrollIndicatorInsets: EdgeInsetsPropType,

//是否支持滚动到顶部
scrollsToTop: PropTypes.bool,

//是否显示水平指示器
showsHorizontalScrollIndicator: PropTypes.bool,

//是否显示竖直指示器
showsVerticalScrollIndicator: PropTypes.bool,
 

三、主要函数

//当正在滚动时调用
onScroll: PropTypes.func,

//当滚动结束时调用
onScrollAnimationEnd: PropTypes.func,

//当内容尺寸改变时调用
onContentSizeChange: PropTypes.func,

四、基本使用

/**
 * Sample React Native App
 * https://github.com/facebook/react-native
 * @flow
 */

import React, { Component } from 'react';

import {
    AppRegistry,
    StyleSheet,
    View,
    Dimensions,
    ScrollView,
    Text
} from 'react-native';

//这里引入了屏幕API，计算屏幕的宽高
let {width, height} = Dimensions.get('window');

export default class ReactNativeDemo extends Component {

    render() {
        return (
            <View style={styles.flex}>
                <ScrollView contentContainerStyle={styles.contentContainer1} >
                    <View style={styles.redView}   ////滚动视图1，垂直滚动
                    />
                </ScrollView>

                <ScrollView
                    contentContainerStyle={styles.contentContainer2} ////滚动视图2，水平滚动
                    horizontal={true}
                    pagingEnabled={true}
                    indicatorStyle={'black'}
                    showsHorizontalScrollIndicator={true}
                    bounces={false}
                >
                    <View style={styles.greenView}><Text style={styles.font}>1</Text></View>
                    <View style={styles.purpleView}><Text style={styles.font}>2</Text></View>
                </ScrollView>
            </View>

        );
    }
}

const styles = StyleSheet.create({
    flex: {
        flex: 1
    },
    contentContainer1: {
        flex: 1/2,
        backgroundColor: 'orange',
        justifyContent: 'center',
        alignItems: 'center'
    },
    redView: {
        backgroundColor:'red',
        height: 100,
        width: 100
    },
    contentContainer2: {
        width: width*2,
        backgroundColor: 'green',
    },
    greenView: {
        width:width,
        backgroundColor: 'green',
        justifyContent: 'center',
        alignItems: 'center'
    },
    purpleView: {
        width:width,
        backgroundColor: 'purple',
        justifyContent: 'center',
        alignItems: 'center'
    },
    font: {
        fontSize: 40,
        fontWeight: 'bold',
        color:'white'
    }
});

AppRegistry.registerComponent('ReactNativeDemo', () => ReactNativeDemo);