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116 lines
3.1 KiB
116 lines
3.1 KiB
// Copyright 2019 The Flutter team. All rights reserved.
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// Use of this source code is governed by a BSD-style license that can be
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// found in the LICENSE file.
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import 'package:flutter/material.dart';
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import 'package:flutter/physics.dart';
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class PhysicsCardDragDemo extends StatelessWidget {
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static const String routeName = '/misc/physics_card';
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@override
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Widget build(BuildContext context) {
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return Scaffold(
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appBar: AppBar(
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title: Text('Spring Physics'),
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),
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body: DraggableCard(
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child: FlutterLogo(
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size: 128,
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),
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),
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);
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}
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}
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/// A draggable card that moves back to [Alignment.center] when it's
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/// released.
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class DraggableCard extends StatefulWidget {
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final Widget child;
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DraggableCard({this.child});
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@override
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_DraggableCardState createState() => _DraggableCardState();
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}
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class _DraggableCardState extends State<DraggableCard>
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with SingleTickerProviderStateMixin {
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AnimationController _controller;
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/// The alignment of the card as it is dragged or being animated.
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///
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/// While the card is being dragged, this value is set to the values computed
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/// in the GestureDetector onPanUpdate callback. If the animation is running,
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/// this value is set to the value of the [_animation].
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var _dragAlignment = Alignment.center;
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Animation<Alignment> _animation;
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final _spring = const SpringDescription(
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mass: 10,
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stiffness: 1000,
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damping: 0.7,
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);
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/// Calculate the velocity relative to the unit interval, [0,1],
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/// used by the animation controller.
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double _normalizeVelocity(Offset velocity, Size size) {
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final normalizedVelocity = Offset(
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velocity.dx / size.width,
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velocity.dy / size.height,
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);
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// Returning negative implies dragging away from center
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return -normalizedVelocity.distance;
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}
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/// Calculates and runs a [SpringSimulation]
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void _runAnimation(Offset velocity, Size size) {
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_animation = _controller.drive(
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AlignmentTween(
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begin: _dragAlignment,
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end: Alignment.center,
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),
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);
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final simulation =
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SpringSimulation(_spring, 0, 1, _normalizeVelocity(velocity, size));
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_controller.animateWith(simulation);
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}
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@override
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void initState() {
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super.initState();
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_controller = AnimationController.unbounded(vsync: this)
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..addListener(() => setState(() => _dragAlignment = _animation.value));
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}
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@override
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void dispose() {
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_controller.dispose();
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super.dispose();
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}
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@override
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Widget build(BuildContext context) {
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final size = MediaQuery.of(context).size;
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return GestureDetector(
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onPanStart: (details) => _controller.stop(canceled: true),
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onPanUpdate: (details) => setState(
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() => _dragAlignment += Alignment(
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details.delta.dx / (size.width / 2),
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details.delta.dy / (size.height / 2),
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),
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),
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onPanEnd: (details) =>
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_runAnimation(details.velocity.pixelsPerSecond, size),
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child: Align(
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alignment: _dragAlignment,
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child: Card(
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child: widget.child,
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),
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),
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);
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}
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}
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