Flutter - AnimatedBuilder ，第一次加载时出现动画/小部件错误

Question

当我第一次加载构建器时，在跳转到正确的尺寸和比例之前，我所有的卡片都是相同的尺寸，有谁知道我可以如何调整它以使它们的尺寸从出发？

奇怪的是，当我用一个装满图像的容器替换我的 Padding & Card 小部件时，它似乎以正确的大小生成，但是我需要它们作为我以后布局的卡片。

（我还计划将其全部放入一个小部件类中，而不是将所有这些代码放入我的 main 中，而只是返回一个 CustomScroller。）

请检查以下 Gif：

Gif Of Animation Glitch Gif of Animation working fine when just container is used

任何修复初始加载的帮助将不胜感激！ :)

import 'package:flutter/material.dart';
import 'package:blink/widget/customScroller.dart';


void main() => runApp(new MyApp());

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

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

  final String title;

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

class _MyHomePageState extends State<MyHomePage> {
  PageController pageController;

  List<String> images = [
    "https://iso.500px.com/wp-content/uploads/2014/07/big-one.jpg",
    "https://encrypted-tbn0.gstatic.com/images?q=tbn:ANd9GcRXRfe-GzBFRQzv8udHMCshqQGAj2JD5SGsR7CoyWP_HqFapJCYSA&s",
    "https://ichef.bbci.co.uk/wwfeatures/live/976_549/images/live/p0/7w/b9/p07wb9xk.jpg",
    "https://images.unsplash.com/photo-1501785888041-af3ef285b470?ixlib=rb-1.2.1&w=1000&q=80"
  ];

  @override
  void initState() {
    // TODO: implement initState
    pageController = PageController(initialPage: 1, viewportFraction: 0.77);
  }

  @override
  Widget build(BuildContext context) {
    return new Scaffold(
        body: PageView.builder(
          controller: pageController,
            itemCount: images.length,
            itemBuilder: (context,position){
            return customScroller(position);
            }),);
  }

  customScroller(int index) {
    return AnimatedBuilder(
      animation: pageController,
      builder: (context, widget) {
        double val = 1;

        if(pageController.position.haveDimensions){
          val = pageController.page - index;
        val = 1 - (val.abs()*0.3).clamp(0.0,1.0);}

        return Center(
          child: SizedBox(
            height: Curves.easeInOut.transform(val) *300,
              width: Curves.easeInOut.transform(val) *400,
            child: widget,
          ),
        );
      },
//      child: Container(
//        margin: EdgeInsets.all(10),
//        child: Image.network(images[index],fit:BoxFit.cover),
//      ),
// When I use the above code as the child instead of the padding with the card in it seems to spawn correctly
        child: Padding(
          padding: EdgeInsets.fromLTRB(0, 15, 0, 15),
          child: Container(
            child: Card(
              color: Colors.white70,
              elevation: 9,
              shape: RoundedRectangleBorder(
                borderRadius: BorderRadius.circular(20.0),
              ),
              clipBehavior: Clip.antiAlias,
              child: Container(
                color: Colors.white,
                padding: EdgeInsets.all(5),
                child: Row(
                  children: <Widget>[
                    Expanded(
                      flex: 2,
                      child: Container(
                        height: double.infinity,
                        child: ClipRRect(
                          borderRadius: BorderRadius.only(
                              topLeft: Radius.circular(20.0),
                              topRight: Radius.circular(0.0),
                              bottomRight: Radius.circular(0.0),
                              bottomLeft: Radius.circular(20.0)),
                          child: new Image.network(
                            images[index],
                            fit: BoxFit.cover,
                          ),
                        ),
                      ),
                    ),
                  ],
                ),
              ),
            ),
          ),
        )

    );
  }
}

Answer 1

您缺少的是 AnimatedBuilder 构建方法仅在有一些动画时运行。不是一开始。所以这就是为什么如果你滚动而不是之前大小会改变的原因。

您的子小部件未使用转换器小部件（或大小框）包装，因此所有索引都保持相同（在开始时 - 构建器尚未运行）。在我的示例中，我还用 SizedBox 包裹了孩子，并给了 val 一些初始值。

工作示例：

import 'package:flutter/material.dart';

void main() => runApp(new MyApp());

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

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

  final String title;

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

class _MyHomePageState extends State<MyHomePage> {
  PageController pageController;

  List<String> images = [
    "https://iso.500px.com/wp-content/uploads/2014/07/big-one.jpg",
    "https://encrypted-tbn0.gstatic.com/images?q=tbn:ANd9GcRXRfe-GzBFRQzv8udHMCshqQGAj2JD5SGsR7CoyWP_HqFapJCYSA&s",
    "https://ichef.bbci.co.uk/wwfeatures/live/976_549/images/live/p0/7w/b9/p07wb9xk.jpg",
    "https://images.unsplash.com/photo-1501785888041-af3ef285b470?ixlib=rb-1.2.1&w=1000&q=80"
  ];

  @override
  void initState() {
    // TODO: implement initState
    pageController = PageController(initialPage: 1, viewportFraction: 0.77);
  }

  @override
  Widget build(BuildContext context) {
    return new Scaffold(
      body: PageView.builder(
          controller: pageController,
          itemCount: images.length,
          itemBuilder: (context, position) {
            return customScroller(position);
          }),
    );
  }

  customScroller(int index) {
    Widget child = Padding(
      padding: EdgeInsets.fromLTRB(0, 15, 0, 15),
      child: Container(
        child: Card(
          color: Colors.white70,
          elevation: 9,
          shape: RoundedRectangleBorder(
            borderRadius: BorderRadius.circular(20.0),
          ),
          clipBehavior: Clip.antiAlias,
          child: Container(
            color: Colors.white,
            padding: EdgeInsets.all(5),
            child: Row(
              children: <Widget>[
                Expanded(
                  flex: 2,
                  child: Container(
                    height: double.infinity,
                    child: ClipRRect(
                      borderRadius: BorderRadius.only(
                          topLeft: Radius.circular(20.0),
                          topRight: Radius.circular(0.0),
                          bottomRight: Radius.circular(0.0),
                          bottomLeft: Radius.circular(20.0)),
                      child: new Image.network(
                        images[index],
                        fit: BoxFit.cover,
                      ),
                    ),
                  ),
                ),
              ],
            ),
          ),
        ),
      ),
    );
    double val = (index == 1)?1:0.7;

    return AnimatedBuilder(
        animation: pageController,
        builder: (context, widget) {
          if (pageController.position.haveDimensions) {
            val = pageController.page - index;
            val = 1 - (val.abs() * 0.3).clamp(0.0, 1.0);
          }
          print("val: $val; index: $index");
          return _getTransformedSizedBox(val, widget);
        },
//      child: Container(
//        margin: EdgeInsets.all(10),
//        child: Image.network(images[index],fit:BoxFit.cover),
//      ),
// When I use the above code as the child instead of the padding with the card in it seems to spawn correctly
        child: _getTransformedSizedBox(val, child));
  }

  _getTransformedSizedBox(double val, Widget widget) {
    return Center(
      child: SizedBox(
        height: Curves.easeInOut.transform(val) * 300,
        width: Curves.easeInOut.transform(val) * 400,
        child: widget,
      ),
    );
  }
}