Document ScrollView API completion

[kikisaints]

The following unchecked properties are needed to complete the ScrollView control integration into RNWCPP.

P1

• snapToInterval
  When set, causes the scroll view to stop at multiples of the value of snapToInterval.
  Not directly supported by ScrollViewer. Can be implemented as snap points (Win 8) on the child of the ScrollViewer.
• snapToOffsets
  When set, causes the scroll view to stop at the defined offsets.
  Not directly supported by ScrollViewer. Can be implemented as snap points (Win 8) on the child of the ScrollViewer.
• snapToStart ScrollView snapToStart #3065
  Use in conjunction with snapToOffsets. By default, the beginning of the list counts as a snap offset. Set snapToStart to false to disable this behavior and allow the list to scroll freely between its start and the first snapToOffsets offset. The default value is true.
  Not directly supported by ScrollViewer. Can be implemented in conjunction with adding snap points (Win 8) to the child of the ScrollViewer.
• snapToEnd ScrollView snapToEnd #3066
  Use in conjuction with snapToOffsets. By default, the end of the list counts as a snap offset. Set snapToEnd to false to disable this behavior and allow the list to scroll freely between its end and the last snapToOffsets offset. The default value is true.
  Not directly supported by ScrollViewer. Can be implemented in conjunction with adding snap points (Win 8) to the child of the ScrollViewer.
• snapToAlignment
  When snapToInterval is set, snapToAlignment will define the relationship of the snapping to the scroll view.
  Not directly supported by ScrollViewer. Can be implemented in conjunction with adding snap points (Win 8) to the child of the ScrollViewer.
• removeClippedSubviews View removeClippedSubviews #3067
  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.
  Not directly supported by ScrollViewer. Seems difficult. Needs deep dive.
• keyboardDismissMode ScrollView keyboardDismissMode #3068
  Determines whether the keyboard gets dismissed in response to a drag.
  Not directly supported by ScrollViewer. Mobile-specific. Could be difficult, needs deep dive.
• scrollEnabled
  When false, the view cannot be scrolled via touch interaction. The default value is true. Note that the view can always be scrolled by calling scrollTo.
  Maps to ScrollViewer.VerticalScrollMode/HorizontalScrollMode (Win 8)
• showsHorizontalScrollIndicator
  When true, shows a horizontal scroll indicator. The default value is true.
  Maps to ScrollViewer.HorizontalScrollBarVisibility (Win 8)
• showsVerticalScrollIndicator
  When true, shows a vertical scroll indicator. The default value is true.
  Maps to ScrollViewer.VerticalScrollBarVisibility (Win 8)

P2

• refreshControl ScrollView refreshControl #3069
  A RefreshControl component, used to provide pull-to-refresh functionality for the ScrollView. Only works for vertical ScrollViews (horizontal prop must be false).
  Not directly supported by ScrollViewer. Could maybe use RefreshContainer from MUX (RS4), or drop down to InteractionTracker (RS1) and build one from scratch.
• onMomentumScrollBegin
  Called when the momentum scroll starts (scroll which occurs as the ScrollView glides to a stop).
  Not directly supported by ScrollViewer. Could hook up to ViewChanging and look at ScrollViewerChangingEventArgs.IsInertial.
• onMomentumScrollEnd
  Called when the momentum scroll ends (scroll which occurs as the ScrollView glides to a stop).
  Not directly supported by ScrollViewer. Could hook up to ViewChanging/ViewChanged and look at ScrollViewerChangingEventArgs.IsInertial.
• stickyHeaderIndices ScrollView stickyHeaderIndices #3070
  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}.
  Not directly supported by ScrollViewer. Seems difficult. Needs deep dive.

P3

• decelerationRate ScrollView decelerationRate #3071
  A floating-point number that determines how quickly the scroll view decelerates after the user lifts their finger.
  Not supported by ScrollViewer.
• pagingEnabled ScrollView pagingEnabled #3072
  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.
  Not directly supported by ScrollViewer. Can be implemented by adding snap points (Win 8) to the child of the ScrollViewer
• keyboardShouldPersistTaps ScrollView keyboardShouldPersistTaps #3073
  Determines when the keyboard should stay visible after a tap.
  Not directly supported by ScrollViewer. Mobile-specific. Could be difficult, needs deep dive.

Already Completed

• horizontal
• onScroll
• onScrollBeginDrag
• onScrollEndDrag
• onContentSizeChange
• contentContainerStyle

Future

alwaysBounceVertical iOS Only endfillColor Android Only overScrollMode Android Only scrollPerfTag Android Only alwaysBounceHorizontal iOS Only automactiallyAdjustcontentInsets iOS Only bounces iOS Only bouncesZoom iOS Only canCancelContentTouches iOS Only centerContent iOS Only contentInset iOS Only contentInsetAdjustmentBehavior iOS Only contentOffset iOS Only directionalLockEnabled iOS Only indicatorStyle iOS Only maximumZoomScale iOS Only minimumZoomScale iOS Only pinchGestureEnabled iOS Only scrollEventThrottle iOS Only scrollIndicatorInsets iOS Only scrollsToTop iOS Only zoomScale iOS Only nestedScrollEnabled Android Only

[christophermussack]

I have a pull request to implement just the snapToInterval and the snapToAlignment to be used by the Universal outlook team.
Besides the code change itself this is also for me to learn the process to check this in.

[chrisglein]

@kikisaints I've broken all the individual items of pending work here out into a Project board: https://github.com/microsoft/react-native-windows/projects/17
We want to move this type of "index of completion" to exist in the repo as markdown files. Coordinate with @SavoySchuler on how to do that for ScrollView as well. I'm assigning this over to you to track that documentation work.

[chrisglein]

All missing APIs are tracked with issues or on the board. We have no immediate plans to create formal per-method API parity documentation, so closing this issue.