flutter 2 SliverPersistentHeader - 滚动期间避免重叠

Question

这是我的代码：

import 'package:all_in_one/cooking/pages/recipe/header/search_bar_header.dart';
import 'package:all_in_one/cooking/pages/recipe/header/welcome_header.dart';
import 'package:flutter/material.dart';

class MyRecipePage extends StatefulWidget {
  final String title;

  MyRecipePage({Key? key, required this.title}) : super(key: key);

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

class _MyRecipePageState extends State<MyRecipePage> {

 
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: CustomScrollView(
        slivers: <Widget>[
          WelcomeHeader(),
          SearchBarHeader(),
          SliverGrid.count(),
        ],
      ) ,

    );
  }
}

class WelcomeHeader extends StatelessWidget {

  @override
  Widget build(BuildContext context) {
    return
        SliverPersistentHeader(
          floating: true,
          delegate: SliverAppBarDelegate(
            minHeight: 0,
            maxHeight: 100,
            child: Container(
              color: Colors.white,
              child: _MyWelcomingHeader(),
            ),
          ),


    );
  }
}

class _MyWelcomingHeader extends StatelessWidget {

  @override
  Widget build(BuildContext context) {
    return Column(
      children: [
        Flexible(
          child: CircleAvatar(
            radius: 57,
            backgroundColor: Colors.grey.shade50,
            child: Image.asset("assets/emoji-food.jpg"),
          ),
        ),
        Flexible(
          child: Padding(
            padding: const EdgeInsets.all(10.0),
            child: Text(
              'Enjoy the recipes',
              style: TextStyle(
                color: Colors.black,
                fontSize: 26.0,
                fontWeight: FontWeight.bold,
              ),
            ),
          ),
        ),
      ],
    );
  }
}


class SearchBarHeader extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return SliverPersistentHeader(
      pinned: true,
      delegate: SliverAppBarDelegate(
        minHeight: 50,
        maxHeight: 50,
        child: Container(
          color: Colors.white,
          child: _MySearchBar(),
        ),
      ),
    );
  }
}

class _MySearchBar extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Row(
      crossAxisAlignment: CrossAxisAlignment.center,
      children: [
        const SizedBox(width: 10),
        const Icon(Icons.search, color: Colors.grey, size: 30),
        const SizedBox(width: 5),
        Text("Search product",
            style: TextStyle(
                color: Colors.grey.shade500, fontSize: 12, fontWeight: FontWeight.w200))
      ],
    );
  }
}

银条Delegate的代码来自这个stackoverflow post

import 'package:flutter/material.dart';
import 'dart:math' as math;

class SliverAppBarDelegate extends SliverPersistentHeaderDelegate {
  final double minHeight;
  final double maxHeight;
  final Widget child;

  SliverAppBarDelegate({
    required this.minHeight,
    required this.maxHeight,
    required this.child,
  });


  @override
  double get minExtent => minHeight;
  @override
  double get maxExtent => math.max(maxHeight, minHeight);
  @override
  Widget build(
      BuildContext context, double shrinkOffset, bool overlapsContent) {
    return SizedBox.expand(child: child);
  }

  @override
  bool shouldRebuild(SliverAppBarDelegate oldDelegate) {
    return maxHeight != oldDelegate.maxHeight ||
        minHeight != oldDelegate.minHeight ||
        child != oldDelegate.child;
  }
}

我的目标是拥有 2 个SliverPersistentHeader，一个固定，一个浮动。 浮动的（第一个）应该在滚动时调整文本和图像的大小..

在下面的截图中，我们可以看到第二个SliverPersistentHeader 与第一个重叠。 我该怎么做才能使 Text 自行调整大小。我尝试像使用 CircleAvatar 一样使用 Flexible，但我无法成功：/

谢谢

Answer 1

我找到了使用不透明度的解决方案，所以我的WelcomeHeader 变为：

import 'package:flutter/material.dart';
import 'dart:math' as math;

class WelcomeHeader extends StatelessWidget {

  @override
  Widget build(BuildContext context) {
    return SliverAppBar(
      backgroundColor: Colors.white,
      pinned: false,
      floating: false,
      snap: false,
      expandedHeight: 120,
      flexibleSpace: _MyWelcomingHeader()
    );
  }
}

class _MyWelcomingHeader extends StatelessWidget {

  @override
  Widget build(BuildContext context) {
    return LayoutBuilder(
        builder: (context, c) {
          final settings = context
              .dependOnInheritedWidgetOfExactType<FlexibleSpaceBarSettings>();
          final deltaExtent = settings!.maxExtent - settings.minExtent;
          final t =
          (1.0 - (settings.currentExtent - settings.minExtent) / deltaExtent)
              .clamp(0.0, 1.0);
          final fadeStart = math.max(0.0, 1.0 - kToolbarHeight / deltaExtent);
          const fadeEnd = 1.0;
          final opacity = 1.0 - Interval(fadeStart, fadeEnd).transform(t);

          return Padding(
            padding: const EdgeInsets.all(8.0),
            child: Opacity(
              opacity: opacity,
              child: Column(
                children: [
                  Flexible(
                    child: CircleAvatar(
                      radius: 57,
                      backgroundColor: Colors.grey.shade50,
                      child: Image.asset("assets/emoji-food.jpg"),
                    ),
                  ),
                  Padding(
                    padding: const EdgeInsets.all(8.0),
                    child: Text(
                      'Enjoy the recipes !',
                      style: TextStyle(
                        color: Colors.black,
                        fontSize: 26.0,
                        fontWeight: FontWeight.bold,
                      ),
                    ),
                  ),
                ],
              ),
            ),
          );
        });
  }
}