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Clarify Draggable docs (#7341)

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More clearly explain the role of child, childWhenDragging, and feedback.

Fixes #6962
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Adam Barth 2017-01-05 11:30:15 -08:00 committed by GitHub
parent 0c6dc598f7
commit c6b9cdf80d
1 changed files with 35 additions and 4 deletions
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39
packages/flutter/lib/src/widgets/drag_target.dart
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@ -62,7 +62,17 @@ enum DragAnchor {
/// When a draggable widget recognizes the start of a drag gesture, it displays
/// a [feedback] widget that tracks the user's finger across the screen. If the
/// user lifts their finger while on top of a [DragTarget], that target is given
/// the opportunity to accept the [data] carried by the draggble.
/// the opportunity to accept the [data] carried by the draggable.
///
/// On multitouch devices, multiple drags can occur simultaneously because there
/// can be multiple pointers in contact with the device at once. To limit the
/// number of simultaneous drags, use the [maxSimultaneousDrags] property. The
/// default is to allow an unlimited number of simultaneous drags.
///
/// This widget displays [child] when zero drags are under way. If
/// [childWhenDragging] is non-null, this widget instead displays
/// [childWhenDragging] when one or more drags are underway. Otherwise, this
/// widget always displays [child].
///
/// See also:
///
@ -95,16 +105,34 @@ class Draggable<T> extends StatefulWidget {
final T data;
/// The widget below this widget in the tree.
///
/// This widget displays [child] when zero drags are under way. If
/// [childWhenDragging] is non-null, this widget instead displays
/// [childWhenDragging] when one or more drags are underway. Otherwise, this
/// widget always displays [child].
///
/// The [feedback] widget is shown under the pointer when a drag is under way.
///
/// To limit the number of simultaneous drags on multitouch devices, see
/// [maxSimultaneousDrags].
final Widget child;
/// The widget to show instead of [child] when a drag is under way.
/// The widget to display instead of [child] when one or more drags are under way.
///
/// If this is null, then [child] will be used instead (and so the
/// drag source representation will change while a drag is under
/// If this is null, then this widget will always display [child] (and so the
/// drag source representation will not change while a drag is under
/// way).
///
/// The [feedback] widget is shown under the pointer when a drag is under way.
///
/// To limit the number of simultaneous drags on multitouch devices, see
/// [maxSimultaneousDrags].
final Widget childWhenDragging;
/// The widget to show under the pointer when a drag is under way.
///
/// See [child] and [childWhenDragging] for information about what is shown
/// at the location of the [Draggable] itself when a drag is under way.
final Widget feedback;
/// The feedbackOffset can be used to set the hit test target point for the
@ -136,6 +164,9 @@ class Draggable<T> extends StatefulWidget {
/// When null, no limit is applied. Set this to 1 if you want to only allow
/// the drag source to have one item dragged at a time. Set this to 0 if you
/// want to prevent the draggable from actually being dragged.
///
/// If you set this property to 1, consider supplying an "empty" widget for
/// [childWhenDragging] to create the illusion of actually moving [child].
final int maxSimultaneousDrags;
/// Called when the draggable starts being dragged.