每次启动应用程序时颤动一次动画（不是第一次运行）

Question

我想在我的主屏幕上使用一些动画，但只在应用启动时使用，因为在使用应用时，用户必须经常导航回主屏幕，而这些动画会导致加载时间变得很烦人，一次又一次地看到......所以, 有没有办法让动画只在应用程序的第一次启动（而不是第一次运行）时处于活动状态，然后在重新启动应用程序之前使其处于非活动状态？

这是一个简单的代码；与我使用的动画的逻辑不同但相似，我的代码太复杂而无法复制粘贴，所以我发送了一个示例代码，我将其发送给另一个问题作为答案；

import 'dart:async';
import 'package:flutter/cupertino.dart';
import 'package:flutter/material.dart';

void main() {
 runApp(MyApp());
}

class MyApp extends StatelessWidget {
 @override
 Widget build(BuildContext context) {
   return MaterialApp(
     title: 'Flutter Demo',
     theme: ThemeData(
       primarySwatch: Colors.blue,
     ),
     home: MyHomePage(title: 'Flutter Demo Home Page'),
   );
 }
}

class MyHomePage extends StatefulWidget {
 MyHomePage({Key key, this.title}) : super(key: key);

 final String title;

 @override
 _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {

 @override
 Widget build(BuildContext context) {
   return Scaffold(
     body: Center(
       child: ListView(
         children: [Container(
           color: Colors.blue,
           height: 1000,
           child: Column(
             mainAxisAlignment: MainAxisAlignment.center,
             crossAxisAlignment: CrossAxisAlignment.center,
             children: <Widget>[
               SlideFadeTransition(
                   delayStart: Duration(milliseconds: 800),
                   offset: 2,
                   child: new Text('Test Text 1')),
               SlideFadeTransition(
                   delayStart: Duration(milliseconds: 1200),
                   offset: 4,
                   child: new Text('Test Text 2'))
             ],
           ),
         ),
           Container(
             color: Colors.red,
             height: 1000,
             child: Column(
               mainAxisAlignment: MainAxisAlignment.center,
               crossAxisAlignment: CrossAxisAlignment.center,
               children: <Widget>[
                 SlideFadeTransition(
                     delayStart: Duration(milliseconds: 1200),
                     offset: 2,
                     child: new Text('Test Text 1')),
                 SlideFadeTransition(
                     delayStart: Duration(milliseconds: 2400),
                     offset: 4,
                     child: new Text('Test Text 2'))
               ],
             ),
           ),
           Container(
             color: Colors.orange,
             height: 1000,
             child: Column(
               mainAxisAlignment: MainAxisAlignment.center,
               crossAxisAlignment: CrossAxisAlignment.center,
               children: <Widget>[
                 SlideFadeTransition(
                     delayStart: Duration(milliseconds: 1200),
                     offset: 2,
                     child: new Text('Test Text 1')),
                 SlideFadeTransition(
                     delayStart: Duration(milliseconds: 2400),
                     offset: 4,
                     child: new Text('Test Text 2'))
               ],
             ),
           ),
 ]
   )
   )
   );
 }
}


enum Direction { vertical, horizontal }

class SlideFadeTransition extends StatefulWidget {
 ///The child on which to apply the given [SlideFadeTransition]
 final Widget child;

 ///The offset by which to slide and [child] into view from [Direction].
 ///Defaults to 0.2
 final double offset;

 ///The curve used to animate the [child] into view.
 ///Defaults to [Curves.easeIn]
 final Curve curve;

 ///The direction from which to animate the [child] into view. [Direction.horizontal]
 ///will make the child slide on x-axis by [offset] and [Direction.vertical] on y-axis.
 ///Defaults to [Direction.vertical]
 final Direction direction;

 ///The delay with which to animate the [child]. Takes in a [Duration] and
 /// defaults to 0.0 seconds
 final Duration delayStart;

 ///The total duration in which the animation completes. Defaults to 800 milliseconds
 final Duration animationDuration;

 SlideFadeTransition({
   @required this.child,
   this.offset = 0.2,
   this.curve = Curves.easeIn,
   this.direction = Direction.vertical,
   this.delayStart = const Duration(seconds: 0),
   this.animationDuration = const Duration(milliseconds: 800),
 });
 @override
 _SlideFadeTransitionState createState() => _SlideFadeTransitionState();
}

class _SlideFadeTransitionState extends State<SlideFadeTransition>
   with SingleTickerProviderStateMixin {
 Animation<Offset> _animationSlide;

 AnimationController _animationController;

 Animation<double> _animationFade;

 @override
 void initState() {
   super.initState();
   _animationController = AnimationController(
     vsync: this,
     duration: widget.animationDuration,
   );

   //configure the animation controller as per the direction
   if (widget.direction == Direction.vertical) {
     _animationSlide =
         Tween<Offset>(begin: Offset(0, widget.offset), end: Offset(0, 0))
             .animate(CurvedAnimation(
           curve: widget.curve,
           parent: _animationController,
         ));
   } else {
     _animationSlide =
         Tween<Offset>(begin: Offset(widget.offset, 0), end: Offset(0, 0))
             .animate(CurvedAnimation(
           curve: widget.curve,
           parent: _animationController,
         ));
   }

   _animationFade =
       Tween<double>(begin: -1.0, end: 1.0).animate(CurvedAnimation(
         curve: widget.curve,
         parent: _animationController,
       ));

   Timer(widget.delayStart, () {
     _animationController.forward();
   });
 }

 @override
 Widget build(BuildContext context) {
   return FadeTransition(
     opacity: _animationFade,
     child: SlideTransition(
       position: _animationSlide,
       child: widget.child,
     ),
   );}}

Answer 1

您可以在下面复制粘贴运行完整代码
第 1 步：您可以定义一个 bool firstRun = true
第 2 步：导航到其他页面时，将 firstRun 设置为 false
第三步：在_SlideFadeTransitionState的build方法中检查是否不是firstRun并直接返回widget.child

return firstRun? FadeTransition(...widget.child) : widget.child

工作演示

代码sn-p

bool firstRun = true;
...
RaisedButton(
        child: Text('Open route'),
        onPressed: () {
          firstRun = false;
          Navigator.push(
            context,
            MaterialPageRoute(builder: (context) => SecondRoute()),
          );
        },
      )
...

  @override
  Widget build(BuildContext context) {
    print('first run ${firstRun}');
    return firstRun? FadeTransition(
      opacity: _animationFade,
      child: SlideTransition(
        position: _animationSlide,
        child: widget.child,
      ),
    ) : widget.child;
  } 

完整代码

import 'dart:async';
import 'package:flutter/cupertino.dart';
import 'package:flutter/material.dart';

void main() {
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

bool firstRun = true;

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key, this.title}) : super(key: key);

  final String title;

  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  @override
  void initState() {
    // TODO: implement initState
    super.initState();
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
        body: Center(
            child: ListView(children: [
      Container(
        color: Colors.blue,
        height: 1000,
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          crossAxisAlignment: CrossAxisAlignment.center,
          children: <Widget>[
            SlideFadeTransition(
                delayStart: Duration(milliseconds: 800),
                offset: 2,
                child: new Text('Test Text 1')),
            SlideFadeTransition(
                delayStart: Duration(milliseconds: 1200),
                offset: 4,
                child: new Text('Test Text 2'))
          ],
        ),
      ),
      Container(
        color: Colors.red,
        height: 1000,
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          crossAxisAlignment: CrossAxisAlignment.center,
          children: <Widget>[
            SlideFadeTransition(
                delayStart: Duration(milliseconds: 1200),
                offset: 2,
                child: new Text('Test Text 1')),
            SlideFadeTransition(
                delayStart: Duration(milliseconds: 2400),
                offset: 4,
                child: new Text('Test Text 2'))
          ],
        ),
      ),
      Container(
        color: Colors.orange,
        height: 1000,
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          crossAxisAlignment: CrossAxisAlignment.center,
          children: <Widget>[
            SlideFadeTransition(
                delayStart: Duration(milliseconds: 1200),
                offset: 2,
                child: new Text('Test Text 1')),
            SlideFadeTransition(
                delayStart: Duration(milliseconds: 2400),
                offset: 4,
                child: new Text('Test Text 2'))
          ],
        ),
      ),
      RaisedButton(
        child: Text('Open route'),
        onPressed: () {
          firstRun = false;
          Navigator.push(
            context,
            MaterialPageRoute(builder: (context) => SecondRoute()),
          );
        },
      ),
    ])));
  }
}

enum Direction { vertical, horizontal }

class SlideFadeTransition extends StatefulWidget {
  ///The child on which to apply the given [SlideFadeTransition]
  final Widget child;

  ///The offset by which to slide and [child] into view from [Direction].
  ///Defaults to 0.2
  final double offset;

  ///The curve used to animate the [child] into view.
  ///Defaults to [Curves.easeIn]
  final Curve curve;

  ///The direction from which to animate the [child] into view. [Direction.horizontal]
  ///will make the child slide on x-axis by [offset] and [Direction.vertical] on y-axis.
  ///Defaults to [Direction.vertical]
  final Direction direction;

  ///The delay with which to animate the [child]. Takes in a [Duration] and
  /// defaults to 0.0 seconds
  final Duration delayStart;

  ///The total duration in which the animation completes. Defaults to 800 milliseconds
  final Duration animationDuration;

  SlideFadeTransition({
    @required this.child,
    this.offset = 0.2,
    this.curve = Curves.easeIn,
    this.direction = Direction.vertical,
    this.delayStart = const Duration(seconds: 0),
    this.animationDuration = const Duration(milliseconds: 800),
  });
  @override
  _SlideFadeTransitionState createState() => _SlideFadeTransitionState();
}

class _SlideFadeTransitionState extends State<SlideFadeTransition>
    with SingleTickerProviderStateMixin {
  Animation<Offset> _animationSlide;

  AnimationController _animationController;

  Animation<double> _animationFade;

  @override
  void initState() {
    super.initState();
    _animationController = AnimationController(
      vsync: this,
      duration: widget.animationDuration,
    );

    //configure the animation controller as per the direction
    if (widget.direction == Direction.vertical) {
      _animationSlide =
          Tween<Offset>(begin: Offset(0, widget.offset), end: Offset(0, 0))
              .animate(CurvedAnimation(
        curve: widget.curve,
        parent: _animationController,
      ));
    } else {
      _animationSlide =
          Tween<Offset>(begin: Offset(widget.offset, 0), end: Offset(0, 0))
              .animate(CurvedAnimation(
        curve: widget.curve,
        parent: _animationController,
      ));
    }

    _animationFade =
        Tween<double>(begin: -1.0, end: 1.0).animate(CurvedAnimation(
      curve: widget.curve,
      parent: _animationController,
    ));

    Timer(widget.delayStart, () {
      _animationController.forward();
    });
  }

  @override
  Widget build(BuildContext context) {
    print('first run ${firstRun}');
    return firstRun? FadeTransition(
      opacity: _animationFade,
      child: SlideTransition(
        position: _animationSlide,
        child: widget.child,
      ),
    ) : widget.child;
  }
}

class SecondRoute extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text("Second Route"),
      ),
      body: Center(
        child: RaisedButton(
          onPressed: () {
            // Navigate back to first route when tapped.
          },
          child: Text('Go back!'),
        ),
      ),
    );
  }
}