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https://github.com/flutter/flutter
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Merge pull request #2382 from Hixie/scroll-member-order
Reorder and document members in ScrollableState
This commit is contained in:
Ian Hickson
commit
222c2ad315
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@ -55,6 +55,31 @@ abstract class Scrollable extends StatefulComponent {
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/// The axis along which this widget should scroll.
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final Axis scrollDirection;
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/// Whether to place first child at the start of the container or
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/// the last child at the end of the container, when the scrollable
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/// has not been scrolled and has no initial scroll offset.
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///
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/// For example, if the [scrollDirection] is [Axis.vertical] and
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/// there are enough items to overflow the container, then
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/// [ViewportAnchor.start] means that the top of the first item
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/// should be aligned with the top of the scrollable with the last
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/// item below the bottom, and [ViewportAnchor.end] means the bottom
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/// of the last item should be aligned with the bottom of the
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/// scrollable, with the first item above the top.
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///
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/// This also affects whether, when an item is added or removed, the
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/// displacement will be towards the first item or the last item.
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/// Continuing the earlier example, if a new item is inserted in the
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/// middle of the list, in the [ViewportAnchor.start] case the items
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/// after it (with greater indices, down to the item with the
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/// highest index) will be pushed down, while in the
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/// [ViewportAnchor.end] case the items before it (with lower
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/// indices, up to the item with the index 0) will be pushed up.
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///
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/// Subclasses may ignore this value if, for instance, they do not
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/// have a concept of an anchor, or have more complicated behavior
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/// (e.g. they would by default put the middle item in the middle of
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/// the container).
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final ViewportAnchor scrollAnchor;
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/// Called whenever this widget starts to scroll.
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@ -153,10 +178,44 @@ abstract class Scrollable extends StatefulComponent {
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ScrollableState createState();
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}
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/// Contains the state for common scrolling behaviors.
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/// Contains the state for common scrolling widgets.
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///
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/// Widgets that subclass [Scrollable] typically use state objects that subclass
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/// [ScrollableState].
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/// Widgets that subclass [Scrollable] typically use state objects
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/// that subclass [ScrollableState].
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///
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/// The main state of a ScrollableState is the "scroll offset", which
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/// is the the logical description of the current scroll position and
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/// is stored in [scrollOffset] as a double. The units of the scroll
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/// offset are defined by the specific subclass. By default, the units
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/// are logical pixels.
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///
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/// A "pixel offset" is a distance in logical pixels (or a velocity in
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/// logical pixels per second). The pixel offset corresponding to the
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/// current scroll position is typically used as the paint offset
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/// argument to the underlying [Viewport] class (or equivalent); see
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/// the [buildContent] method.
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///
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/// A "pixel delta" is an [Offset] that describes a two-dimensional
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/// distance as reported by input events. If the scrolling convention
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/// is axis-aligned (as in a vertical scrolling list or a horizontal
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/// scrolling list), then the pixel delta will consist of a pixel
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/// offset in the scroll axis, and a value in the other axis that is
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/// either ignored (when converting to a scroll offset) or set to zero
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/// (when converting a scroll offset to a pixel delta).
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///
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/// If the units of the scroll offset are not logical pixels, then a
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/// mapping must be made from logical pixels (as used by incoming
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/// input events) and the scroll offset (as stored internally). To
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/// provide this mapping, override the [pixelOffsetToScrollOffset] and
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/// [scrollOffsetToPixelOffset] methods.
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///
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/// If the scrollable is not providing axis-aligned scrolling, then,
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/// to convert pixel deltas to scroll offsets and vice versa, override
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/// the [pixelDeltaToScrollOffset] and [scrollOffsetToPixelOffset]
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/// methods. By default, these assume an axis-aligned scroll behavior
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/// along the [config.scrollDirection] axis and are implemented in
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/// terms of the [pixelOffsetToScrollOffset] and
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/// [scrollOffsetToPixelOffset] methods.
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abstract class ScrollableState<T extends Scrollable> extends State<T> {
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void initState() {
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super.initState();
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@ -166,6 +225,11 @@ abstract class ScrollableState<T extends Scrollable> extends State<T> {
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AnimationController _controller;
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void dispose() {
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_controller.stop();
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super.dispose();
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}
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/// The current scroll offset.
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///
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/// The scroll offset is applied to the child widget along the scroll
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@ -178,6 +242,8 @@ abstract class ScrollableState<T extends Scrollable> extends State<T> {
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/// Scrollable gesture handlers convert their incoming values with this method.
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/// Subclasses that define scrollOffset in units other than pixels must
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/// override this method.
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///
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/// This function should be the inverse of [scrollOffsetToPixelOffset].
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double pixelOffsetToScrollOffset(double pixelOffset) {
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switch (config.scrollAnchor) {
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case ViewportAnchor.start:
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@ -189,6 +255,9 @@ abstract class ScrollableState<T extends Scrollable> extends State<T> {
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}
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}
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/// Convert a scrollOffset value to the number of pixels to which it corresponds.
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///
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/// This function should be the inverse of [pixelOffsetToScrollOffset].
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double scrollOffsetToPixelOffset(double scrollOffset) {
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switch (config.scrollAnchor) {
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case ViewportAnchor.start:
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@ -200,6 +269,9 @@ abstract class ScrollableState<T extends Scrollable> extends State<T> {
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/// Returns the scroll offset component of the given pixel delta, accounting
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/// for the scroll direction and scroll anchor.
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///
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/// A pixel delta is an [Offset] in pixels. Typically this function
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/// is implemented in terms of [pixelOffsetToScrollOffset].
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double pixelDeltaToScrollOffset(Offset pixelDelta) {
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switch (config.scrollDirection) {
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case Axis.horizontal:
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@ -211,6 +283,8 @@ abstract class ScrollableState<T extends Scrollable> extends State<T> {
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/// Returns a two-dimensional representation of the scroll offset, accounting
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/// for the scroll direction and scroll anchor.
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///
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/// See the definition of [ScrollableState] for more details.
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Offset scrollOffsetToPixelDelta(double scrollOffset) {
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switch (config.scrollDirection) {
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case Axis.horizontal:
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@ -220,79 +294,19 @@ abstract class ScrollableState<T extends Scrollable> extends State<T> {
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}
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}
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ScrollBehavior _scrollBehavior;
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/// Subclasses should override this function to create the [ScrollBehavior]
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/// they desire.
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ScrollBehavior createScrollBehavior();
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/// The current scroll behavior of this widget.
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///
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/// Scroll behaviors control where the boundaries of the scrollable are placed
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/// and how the scrolling physics should behave near those boundaries and
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/// after the user stops directly manipulating the scrollable.
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ScrollBehavior get scrollBehavior {
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if (_scrollBehavior == null)
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_scrollBehavior = createScrollBehavior();
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return _scrollBehavior;
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return _scrollBehavior ??= createScrollBehavior();
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}
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ScrollBehavior _scrollBehavior;
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Map<Type, GestureRecognizerFactory> buildGestureDetectors() {
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if (scrollBehavior.isScrollable) {
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switch (config.scrollDirection) {
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case Axis.vertical:
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return <Type, GestureRecognizerFactory>{
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VerticalDragGestureRecognizer: (VerticalDragGestureRecognizer recognizer) {
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return (recognizer ??= new VerticalDragGestureRecognizer())
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..onStart = _handleDragStart
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..onUpdate = _handleDragUpdate
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..onEnd = _handleDragEnd;
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}
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};
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case Axis.horizontal:
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return <Type, GestureRecognizerFactory>{
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HorizontalDragGestureRecognizer: (HorizontalDragGestureRecognizer recognizer) {
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return (recognizer ??= new HorizontalDragGestureRecognizer())
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..onStart = _handleDragStart
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..onUpdate = _handleDragUpdate
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..onEnd = _handleDragEnd;
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}
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};
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}
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}
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return const <Type, GestureRecognizerFactory>{};
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}
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final GlobalKey _gestureDetectorKey = new GlobalKey();
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void updateGestureDetector() {
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_gestureDetectorKey.currentState.replaceGestureRecognizers(buildGestureDetectors());
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}
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Widget build(BuildContext context) {
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return new RawGestureDetector(
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key: _gestureDetectorKey,
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gestures: buildGestureDetectors(),
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behavior: HitTestBehavior.opaque,
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child: new Listener(
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child: buildContent(context),
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onPointerDown: _handlePointerDown
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)
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);
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}
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/// Subclasses should override this function to build the interior of their
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/// scrollable widget. Scrollable wraps the returned widget in a
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/// [GestureDetector] to observe the user's interaction with this widget and
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/// to adjust the scroll offset accordingly.
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Widget buildContent(BuildContext context);
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Future _animateTo(double newScrollOffset, Duration duration, Curve curve) {
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_controller.stop();
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_controller.value = scrollOffset;
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_dispatchOnScrollStartIfNeeded();
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return _controller.animateTo(newScrollOffset, duration: duration, curve: curve).then(_dispatchOnScrollEndIfNeeded);
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}
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/// Subclasses should override this function to create the [ScrollBehavior]
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/// they desire.
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ScrollBehavior createScrollBehavior();
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bool _scrollOffsetIsInBounds(double scrollOffset) {
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if (scrollBehavior is! ExtentScrollBehavior)
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@ -301,25 +315,105 @@ abstract class ScrollableState<T extends Scrollable> extends State<T> {
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return scrollOffset >= behavior.minScrollOffset && scrollOffset < behavior.maxScrollOffset;
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}
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Simulation _createFlingSimulation(double scrollVelocity) {
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final Simulation simulation = scrollBehavior.createFlingScrollSimulation(scrollOffset, scrollVelocity);
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if (simulation != null) {
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final double endVelocity = pixelOffsetToScrollOffset(kPixelScrollTolerance.velocity).abs() * (scrollVelocity < 0.0 ? -1.0 : 1.0);
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final double endDistance = pixelOffsetToScrollOffset(kPixelScrollTolerance.distance).abs();
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simulation.tolerance = new Tolerance(velocity: endVelocity, distance: endDistance);
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}
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return simulation;
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void _handleAnimationChanged() {
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_setScrollOffset(_controller.value);
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}
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void _setScrollOffset(double newScrollOffset) {
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if (_scrollOffset == newScrollOffset)
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return;
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setState(() {
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_scrollOffset = newScrollOffset;
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});
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PageStorage.of(context)?.writeState(context, _scrollOffset);
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new ScrollNotification(this, _scrollOffset).dispatch(context);
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final needsScrollStart = !_isBetweenOnScrollStartAndOnScrollEnd;
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if (needsScrollStart) {
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dispatchOnScrollStart();
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assert(_isBetweenOnScrollStartAndOnScrollEnd);
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}
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dispatchOnScroll();
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assert(_isBetweenOnScrollStartAndOnScrollEnd);
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if (needsScrollStart)
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dispatchOnScrollEnd();
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}
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/// Scroll this widget by the given scroll delta.
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///
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/// If a non-null [duration] is provided, the widget will animate to the new
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/// scroll offset over the given duration with the given curve.
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Future scrollBy(double scrollDelta, { Duration duration, Curve curve: Curves.ease }) {
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double newScrollOffset = scrollBehavior.applyCurve(_scrollOffset, scrollDelta);
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return scrollTo(newScrollOffset, duration: duration, curve: curve);
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}
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/// Scroll this widget to the given scroll offset.
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///
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/// If a non-null [duration] is provided, the widget will animate to the new
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/// scroll offset over the given duration with the given curve.
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///
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/// This function does not accept a zero duration. To jump-scroll to
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/// the new offset, do not provide a duration, rather than providing
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/// a zero duration.
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Future scrollTo(double newScrollOffset, { Duration duration, Curve curve: Curves.ease }) {
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if (newScrollOffset == _scrollOffset)
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return new Future.value();
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if (duration == null) {
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_controller.stop();
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_setScrollOffset(newScrollOffset);
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return new Future.value();
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}
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assert(duration > Duration.ZERO);
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return _animateTo(newScrollOffset, duration, curve);
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}
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Future _animateTo(double newScrollOffset, Duration duration, Curve curve) {
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_controller.stop();
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_controller.value = scrollOffset;
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_dispatchOnScrollStartIfNeeded();
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return _controller.animateTo(newScrollOffset, duration: duration, curve: curve).then(_dispatchOnScrollEndIfNeeded);
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}
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/// Fling the scroll offset with the given velocity.
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///
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/// Calling this function starts a physics-based animation of the scroll
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/// offset with the given value as the initial velocity. The physics
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/// simulation used is determined by the scroll behavior.
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Future fling(double scrollVelocity) {
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if (scrollVelocity != 0.0 || !_controller.isAnimating)
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return _startToEndAnimation(scrollVelocity);
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return new Future.value();
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}
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/// Animate the scroll offset to a value with a local minima of energy.
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///
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/// Calling this function starts a physics-based animation of the scroll
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/// offset either to a snap point or to within the scrolling bounds. The
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/// physics simulation used is determined by the scroll behavior.
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Future settleScrollOffset() {
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return _startToEndAnimation(0.0);
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}
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Future _startToEndAnimation(double scrollVelocity) {
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_controller.stop();
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Simulation simulation = _createSnapSimulation(scrollVelocity) ?? _createFlingSimulation(scrollVelocity);
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if (simulation == null)
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return new Future.value();
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_dispatchOnScrollStartIfNeeded();
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return _controller.animateWith(simulation).then(_dispatchOnScrollEndIfNeeded);
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}
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/// Whether this scrollable should attempt to snap scroll offsets.
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bool get shouldSnapScrollOffset => config.snapOffsetCallback != null;
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/// Returns the snapped offset closest to the given scroll offset.
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double snapScrollOffset(double scrollOffset) {
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RenderBox box = context.findRenderObject();
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return config.snapOffsetCallback == null ? scrollOffset : config.snapOffsetCallback(scrollOffset, box.size);
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}
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/// Whether this scrollable should attempt to snap scroll offsets.
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bool get shouldSnapScrollOffset => config.snapOffsetCallback != null;
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Simulation _createSnapSimulation(double scrollVelocity) {
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if (!shouldSnapScrollOffset || scrollVelocity == 0.0 || !_scrollOffsetIsInBounds(scrollOffset))
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return null;
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@ -349,106 +443,41 @@ abstract class ScrollableState<T extends Scrollable> extends State<T> {
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return new ClampedSimulation(toSnapSimulation, xMin: scrollOffsetMin, xMax: scrollOffsetMax);
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}
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Future _startToEndAnimation(double scrollVelocity) {
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_controller.stop();
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Simulation simulation = _createSnapSimulation(scrollVelocity) ?? _createFlingSimulation(scrollVelocity);
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if (simulation == null)
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return new Future.value();
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_dispatchOnScrollStartIfNeeded();
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return _controller.animateWith(simulation).then(_dispatchOnScrollEndIfNeeded);
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}
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void dispose() {
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_controller.stop();
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super.dispose();
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}
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void _handleAnimationChanged() {
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_setScrollOffset(_controller.value);
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}
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void _setScrollOffset(double newScrollOffset) {
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if (_scrollOffset == newScrollOffset)
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return;
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setState(() {
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_scrollOffset = newScrollOffset;
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});
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PageStorage.of(context)?.writeState(context, _scrollOffset);
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new ScrollNotification(this, _scrollOffset).dispatch(context);
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final needsScrollStart = !_isBetweenOnScrollStartAndOnScrollEnd;
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if (needsScrollStart) {
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dispatchOnScrollStart();
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assert(_isBetweenOnScrollStartAndOnScrollEnd);
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Simulation _createFlingSimulation(double scrollVelocity) {
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final Simulation simulation = scrollBehavior.createFlingScrollSimulation(scrollOffset, scrollVelocity);
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if (simulation != null) {
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final double endVelocity = pixelOffsetToScrollOffset(kPixelScrollTolerance.velocity).abs() * (scrollVelocity < 0.0 ? -1.0 : 1.0);
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final double endDistance = pixelOffsetToScrollOffset(kPixelScrollTolerance.distance).abs();
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simulation.tolerance = new Tolerance(velocity: endVelocity, distance: endDistance);
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}
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dispatchOnScroll();
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assert(_isBetweenOnScrollStartAndOnScrollEnd);
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if (needsScrollStart)
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dispatchOnScrollEnd();
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return simulation;
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}
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/// Scroll this widget to the given scroll offset.
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///
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/// If a non-null [duration] is provided, the widget will animate to the new
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/// scroll offset over the given duration with the given curve.
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///
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/// This function does not accept a zero duration. To jump-scroll to
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/// the new offset, do not provide a duration, rather than providing
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/// a zero duration.
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Future scrollTo(double newScrollOffset, { Duration duration, Curve curve: Curves.ease }) {
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if (newScrollOffset == _scrollOffset)
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return new Future.value();
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if (duration == null) {
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_controller.stop();
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_setScrollOffset(newScrollOffset);
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return new Future.value();
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}
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assert(duration > Duration.ZERO);
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return _animateTo(newScrollOffset, duration, curve);
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}
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/// Scroll this widget by the given scroll delta.
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///
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/// If a non-null [duration] is provided, the widget will animate to the new
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/// scroll offset over the given duration with the given curve.
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Future scrollBy(double scrollDelta, { Duration duration, Curve curve: Curves.ease }) {
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double newScrollOffset = scrollBehavior.applyCurve(_scrollOffset, scrollDelta);
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return scrollTo(newScrollOffset, duration: duration, curve: curve);
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}
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/// Fling the scroll offset with the given velocity.
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///
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/// Calling this function starts a physics-based animation of the scroll
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/// offset with the given value as the initial velocity. The physics
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/// simulation used is determined by the scroll behavior.
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Future fling(double scrollVelocity) {
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if (scrollVelocity != 0.0 || !_controller.isAnimating)
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return _startToEndAnimation(scrollVelocity);
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return new Future.value();
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}
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/// Animate the scroll offset to a value with a local minima of energy.
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///
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/// Calling this function starts a physics-based animation of the scroll
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/// offset either to a snap point or to within the scrolling bounds. The
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/// physics simulation used is determined by the scroll behavior.
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Future settleScrollOffset() {
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return _startToEndAnimation(0.0);
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}
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bool _isBetweenOnScrollStartAndOnScrollEnd = false;
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/// Calls the onScroll callback.
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///
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/// Subclasses can override this function to hook the scroll callback.
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void dispatchOnScroll() {
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assert(_isBetweenOnScrollStartAndOnScrollEnd);
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if (config.onScroll != null)
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config.onScroll(_scrollOffset);
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}
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void _handlePointerDown(_) {
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_controller.stop();
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}
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void _handleDragStart(_) {
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_dispatchOnScrollStartIfNeeded();
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}
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void _dispatchOnScrollStartIfNeeded() {
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if (!_isBetweenOnScrollStartAndOnScrollEnd)
|
||||
dispatchOnScrollStart();
|
||||
}
|
||||
|
||||
void _dispatchOnScrollEndIfNeeded(_) {
|
||||
if (_isBetweenOnScrollStartAndOnScrollEnd)
|
||||
dispatchOnScrollEnd();
|
||||
}
|
||||
|
||||
/// Calls the onScrollStart callback.
|
||||
///
|
||||
/// Subclasses can override this function to hook the scroll start callback.
|
||||
|
|
@ -459,13 +488,19 @@ abstract class ScrollableState<T extends Scrollable> extends State<T> {
|
|||
config.onScrollStart(_scrollOffset);
|
||||
}
|
||||
|
||||
/// Calls the onScroll callback.
|
||||
///
|
||||
/// Subclasses can override this function to hook the scroll callback.
|
||||
void dispatchOnScroll() {
|
||||
assert(_isBetweenOnScrollStartAndOnScrollEnd);
|
||||
if (config.onScroll != null)
|
||||
config.onScroll(_scrollOffset);
|
||||
void _handleDragUpdate(double delta) {
|
||||
scrollBy(pixelOffsetToScrollOffset(delta));
|
||||
}
|
||||
|
||||
Future _handleDragEnd(Velocity velocity) {
|
||||
double scrollVelocity = pixelDeltaToScrollOffset(velocity.pixelsPerSecond) / Duration.MILLISECONDS_PER_SECOND;
|
||||
// The gesture velocity properties are pixels/second, config min,max limits are pixels/ms
|
||||
return fling(scrollVelocity.clamp(-kMaxFlingVelocity, kMaxFlingVelocity)).then(_dispatchOnScrollEndIfNeeded);
|
||||
}
|
||||
|
||||
void _dispatchOnScrollEndIfNeeded(_) {
|
||||
if (_isBetweenOnScrollStartAndOnScrollEnd)
|
||||
dispatchOnScrollEnd();
|
||||
}
|
||||
|
||||
/// Calls the dispatchOnScrollEnd callback.
|
||||
|
|
@ -478,23 +513,82 @@ abstract class ScrollableState<T extends Scrollable> extends State<T> {
|
|||
config.onScrollEnd(_scrollOffset);
|
||||
}
|
||||
|
||||
void _handlePointerDown(_) {
|
||||
_controller.stop();
|
||||
final GlobalKey _gestureDetectorKey = new GlobalKey();
|
||||
|
||||
Widget build(BuildContext context) {
|
||||
return new RawGestureDetector(
|
||||
key: _gestureDetectorKey,
|
||||
gestures: buildGestureDetectors(),
|
||||
behavior: HitTestBehavior.opaque,
|
||||
child: new Listener(
|
||||
child: buildContent(context),
|
||||
onPointerDown: _handlePointerDown
|
||||
)
|
||||
);
|
||||
}
|
||||
|
||||
void _handleDragStart(_) {
|
||||
_dispatchOnScrollStartIfNeeded();
|
||||
/// Fixes up the gesture detector to listen to the appropriate
|
||||
/// gestures based on the current information about the layout.
|
||||
///
|
||||
/// This method should be called from the
|
||||
/// [onPaintOffsetUpdateNeeded] or [onExtentsChanged] handler given
|
||||
/// to the [Viewport] or equivalent used by the subclass's
|
||||
/// [buildContent] method. See the [buildContent] method's
|
||||
/// description for details.
|
||||
void updateGestureDetector() {
|
||||
_gestureDetectorKey.currentState.replaceGestureRecognizers(buildGestureDetectors());
|
||||
}
|
||||
|
||||
void _handleDragUpdate(double delta) {
|
||||
scrollBy(pixelOffsetToScrollOffset(delta));
|
||||
/// Return the gesture detectors, in the form expected by
|
||||
/// [RawGestureDetector.gestures] and
|
||||
/// [RawGestureDetectorState.replaceGestureRecognizers], that are
|
||||
/// applicable to this [Scrollable] in its current state.
|
||||
///
|
||||
/// This is called by [build] and [updateGestureDetector].
|
||||
Map<Type, GestureRecognizerFactory> buildGestureDetectors() {
|
||||
if (scrollBehavior.isScrollable) {
|
||||
switch (config.scrollDirection) {
|
||||
case Axis.vertical:
|
||||
return <Type, GestureRecognizerFactory>{
|
||||
VerticalDragGestureRecognizer: (VerticalDragGestureRecognizer recognizer) {
|
||||
return (recognizer ??= new VerticalDragGestureRecognizer())
|
||||
..onStart = _handleDragStart
|
||||
..onUpdate = _handleDragUpdate
|
||||
..onEnd = _handleDragEnd;
|
||||
}
|
||||
};
|
||||
case Axis.horizontal:
|
||||
return <Type, GestureRecognizerFactory>{
|
||||
HorizontalDragGestureRecognizer: (HorizontalDragGestureRecognizer recognizer) {
|
||||
return (recognizer ??= new HorizontalDragGestureRecognizer())
|
||||
..onStart = _handleDragStart
|
||||
..onUpdate = _handleDragUpdate
|
||||
..onEnd = _handleDragEnd;
|
||||
}
|
||||
};
|
||||
}
|
||||
}
|
||||
return const <Type, GestureRecognizerFactory>{};
|
||||
}
|
||||
|
||||
Future _handleDragEnd(Velocity velocity) {
|
||||
double scrollVelocity = pixelDeltaToScrollOffset(velocity.pixelsPerSecond) / Duration.MILLISECONDS_PER_SECOND;
|
||||
// The gesture velocity properties are pixels/second, config min,max limits are pixels/ms
|
||||
return fling(scrollVelocity.clamp(-kMaxFlingVelocity, kMaxFlingVelocity)).then(_dispatchOnScrollEndIfNeeded);
|
||||
}
|
||||
/// Subclasses should override this function to build the interior of their
|
||||
/// scrollable widget. Scrollable wraps the returned widget in a
|
||||
/// [GestureDetector] to observe the user's interaction with this widget and
|
||||
/// to adjust the scroll offset accordingly.
|
||||
///
|
||||
/// The widgets used by this method should be widgets that provide a
|
||||
/// layout-time callback that reports the sizes that are relevant to
|
||||
/// the scroll offset (typically the size of the scrollable
|
||||
/// container and the scrolled contents). [Viewport] and
|
||||
/// [MixedViewport] provide an [onPaintOffsetUpdateNeeded] callback
|
||||
/// for this purpose; [GridViewport], [ListViewport], and
|
||||
/// [LazyListViewport] provide an [onExtentsChanged] callback for
|
||||
/// this purpose.
|
||||
///
|
||||
/// This callback should be used to update the scroll behavior, if
|
||||
/// necessary, and then to call [updateGestureDetector] to update
|
||||
/// the gesture detectors accordingly.
|
||||
Widget buildContent(BuildContext context);
|
||||
}
|
||||
|
||||
/// Indicates that a descendant scrollable has scrolled.
|
||||
|
|
|
|||
Loading…
Reference in a new issue