Flutter – 径向英雄动画

径向变换意味着将圆形变成方形。在径向英雄动画中，英雄也是如此。在Flutter， Hero Widget用于创建英雄动画。这里的英雄指的是在屏幕之间移动的小部件。这是应用程序中使用的最基本的动画类型之一，尤其是当应用程序处理图像等媒体时。简单地说，英雄动画就是英雄从一个屏幕飞到另一个屏幕。

创建径向英雄动画时会发生以下过程：

• RadialExpansion Widget用于包裹英雄。
• 英雄的大小会随着它飞过路线而改变，并且英雄会采用孩子的大小。
• 两个重叠的剪辑形成 RadialExpansion 动画。
• PageRouteBuilder用于构建英雄的目的地。
• 所有手势都由InkWell 小部件处理。

下图显示了英雄在时间 = 0 到时间 =1 的径向变换。

RadialExpansion 小部件的工作方式如下所示：

现在让我们构建一个简单的应用程序，其中包含三个英雄，单击它们时会发生径向变换。英雄将存储在flutter应用程序的以下文件夹中：

flutter_app/assets/images/.....

确保在 pubspec.yaml 文件中添加依赖项，如下所示：

现在让我们构建主。dart文件：

Dart

import 'dart:math' as math;
  
import 'package:flutter/cupertino.dart';
import 'package:flutter/material.dart';
import 'package:flutter/scheduler.dart' show timeDilation;
  
class Photo extends StatelessWidget {
  Photo({ Key key, this.photo, this.color, this.onTap }) : super(key: key);
  
  final String photo;
  final Color color;
  final VoidCallback onTap;
  
  Widget build(BuildContext context) {
    return Material(
      color: Theme.of(context).primaryColor.withOpacity(0.25),
      child: InkWell(
        onTap: onTap,
        child: LayoutBuilder(
          builder: (BuildContext context, BoxConstraints size) {
            return Image.asset(
              photo,
              fit: BoxFit.contain,
            );
          },
        ),
      ),
    );
  }
}
  
class RadialExpansion extends StatelessWidget {
  RadialExpansion({
    Key key,
    this.maxRadius,
    this.child,
  }) : clipRectSize = 2.0 * (maxRadius / math.sqrt2),
        super(key: key);
  
  final double maxRadius;
  final clipRectSize;
  final Widget child;
  
  @override
  Widget build(BuildContext context) {
    return ClipOval(
      child: Center(
        child: SizedBox(
          width: clipRectSize,
          height: clipRectSize,
          child: ClipRect(
            child: child,
          ),
        ),
      ),
    );
  }
}
  
class RadialExpansionDemo extends StatelessWidget {
  static const double kMinRadius = 32.0;
  static const double kMaxRadius = 128.0;
  static const opacityCurve = const Interval(0.0, 0.75, curve: Curves.fastOutSlowIn);
  
  static RectTween _createRectTween(Rect begin, Rect end) {
    return MaterialRectCenterArcTween(begin: begin, end: end);
  }
  
  static Widget _buildPage(BuildContext context, String imageName, String description) {
    return Container(
      color: Theme.of(context).canvasColor,
      child: Center(
        child: Card(
          elevation: 8.0,
          child: Column(
            mainAxisSize: MainAxisSize.min,
            children: [
              SizedBox(
                width: kMaxRadius * 2.0,
                height: kMaxRadius * 2.0,
                child: Hero(
                  createRectTween: _createRectTween,
                  tag: imageName,
                  child: RadialExpansion(
                    maxRadius: kMaxRadius,
                    child: Photo(
                      photo: imageName,
                      onTap: () {
                        Navigator.of(context).pop();
                      },
                    ),
                  ),
                ),
              ),
              Text(
                description,
                style: TextStyle(fontWeight: FontWeight.bold),
                textScaleFactor: 3.0,
              ),
              const SizedBox(height: 20.0),
            ],
          ),
        ),
      ),
    );
  }
  
  Widget _buildHero(BuildContext context, String imageName, String description) {
    return Container(
      width: kMinRadius * 3.0,
      height: kMinRadius * 3.0,
      child: Hero(
        createRectTween: _createRectTween,
        tag: imageName,
        child: RadialExpansion(
          maxRadius: kMaxRadius,
          child: Photo(
            photo: imageName,
            onTap: () {
              Navigator.of(context).push(
                PageRouteBuilder(
                  pageBuilder: (BuildContext context,
                                Animation animation,
                                Animation secondaryAnimation) {
                    return AnimatedBuilder(
                        animation: animation,
                        builder: (BuildContext context, Widget child) {
                          return Opacity(
                            opacity: opacityCurve.transform(animation.value),
                            child: _buildPage(context, imageName, description,),
  
                          );
                        }
                    );
                  },
                ),
              );
            },
          ),
        ),
      ),
    );
  }
  
  @override
  Widget build(BuildContext context) {
    // animation speed.
    timeDilation = 4.0;
  
    return Scaffold(
      appBar: AppBar(
        title: const Text('GeeksForGeeks'),
        backgroundColor: Colors.green,
      ),
      body: Container(
        padding: const EdgeInsets.all(33.0),
        alignment: FractionalOffset.bottomLeft,
        child: Row(
          mainAxisAlignment: MainAxisAlignment.spaceBetween,
          children: [
            _buildHero(context, 'assets/images/aquaman.png', 'Aquaman'),
            _buildHero(context, 'assets/images/superman.jpg', 'Superman'),
            _buildHero(context, 'assets/images/wonderwomen.jpg', 'Wonderwomen'),
          ],
        ),
      ),
    );
  }
}
  
void main() {
  runApp(MaterialApp(home: RadialExpansionDemo()));
}

输出：

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