examples/flutter_gallery/lib/gallery/home.dart

// Copyright 2016 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

import 'package:flutter/foundation.dart';
import 'package:flutter/material.dart';

import 'drawer.dart';
import 'item.dart';
import 'theme.dart';

const double _kFlexibleSpaceMaxHeight = 256.0;
const String _kGalleryAssetsPackage = 'flutter_gallery_assets';

class _BackgroundLayer {
  _BackgroundLayer({ int level, double parallax })
    : assetName = 'appbar/appbar_background_layer$level.png',
      assetPackage = _kGalleryAssetsPackage,
      parallaxTween = new Tween<double>(begin: 0.0, end: parallax);
  final String assetName;
  final String assetPackage;
  final Tween<double> parallaxTween;
}

final List<_BackgroundLayer> _kBackgroundLayers = <_BackgroundLayer>[
  new _BackgroundLayer(level: 0, parallax: _kFlexibleSpaceMaxHeight),
  new _BackgroundLayer(level: 1, parallax: _kFlexibleSpaceMaxHeight),
  new _BackgroundLayer(level: 2, parallax: _kFlexibleSpaceMaxHeight / 2.0),
  new _BackgroundLayer(level: 3, parallax: _kFlexibleSpaceMaxHeight / 4.0),
  new _BackgroundLayer(level: 4, parallax: _kFlexibleSpaceMaxHeight / 2.0),
  new _BackgroundLayer(level: 5, parallax: _kFlexibleSpaceMaxHeight)
];

class _AppBarBackground extends StatelessWidget {
  const _AppBarBackground({ Key key, this.animation }) : super(key: key);

  final Animation<double> animation;

  @override
  Widget build(BuildContext context) {
    return new AnimatedBuilder(
      animation: animation,
      builder: (BuildContext context, Widget child) {
        return new Stack(
          children: _kBackgroundLayers.map((_BackgroundLayer layer) {
            return new Positioned(
              top: -layer.parallaxTween.evaluate(animation),
              left: 0.0,
              right: 0.0,
              bottom: 0.0,
              child: new Image.asset(
                layer.assetName,
                package: layer.assetPackage,
                fit: BoxFit.cover,
                height: _kFlexibleSpaceMaxHeight
              )
            );
          }).toList()
        );
      }
    );
  }
}

class GalleryHome extends StatefulWidget {
  const GalleryHome({
    Key key,
    this.galleryTheme,
    @required this.onThemeChanged,
    this.timeDilation,
    @required this.onTimeDilationChanged,
    this.textScaleFactor,
    this.onTextScaleFactorChanged,
    this.showPerformanceOverlay,
    this.onShowPerformanceOverlayChanged,
    this.checkerboardRasterCacheImages,
    this.onCheckerboardRasterCacheImagesChanged,
    this.checkerboardOffscreenLayers,
    this.onCheckerboardOffscreenLayersChanged,
    this.onPlatformChanged,
    this.overrideDirection: TextDirection.ltr,
    this.onOverrideDirectionChanged,
    this.onSendFeedback,
  }) : assert(onThemeChanged != null),
       assert(onTimeDilationChanged != null),
       super(key: key);

  // In checked mode our MaterialApp will show the default "debug" banner.
  // Otherwise show the "preview" banner.
  static bool showPreviewBanner = true;

  final GalleryTheme galleryTheme;
  final ValueChanged<GalleryTheme> onThemeChanged;

  final double timeDilation;
  final ValueChanged<double> onTimeDilationChanged;

  final double textScaleFactor;
  final ValueChanged<double> onTextScaleFactorChanged;

  final bool showPerformanceOverlay;
  final ValueChanged<bool> onShowPerformanceOverlayChanged;

  final bool checkerboardRasterCacheImages;
  final ValueChanged<bool> onCheckerboardRasterCacheImagesChanged;

  final bool checkerboardOffscreenLayers;
  final ValueChanged<bool> onCheckerboardOffscreenLayersChanged;

  final ValueChanged<TargetPlatform> onPlatformChanged;

  final TextDirection overrideDirection;
  final ValueChanged<TextDirection> onOverrideDirectionChanged;

  final VoidCallback onSendFeedback;

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

class GalleryHomeState extends State<GalleryHome> with SingleTickerProviderStateMixin {
  static final GlobalKey<ScaffoldState> _scaffoldKey = new GlobalKey<ScaffoldState>();

  AnimationController _controller;

  @override
  void initState() {
    super.initState();
    _controller = new AnimationController(
      duration: const Duration(milliseconds: 600),
      debugLabel: 'preview banner',
      vsync: this,
    )..forward();
  }

  @override
  void dispose() {
    _controller.dispose();
    super.dispose();
  }

  List<Widget> _galleryListItems() {
    final List<Widget> listItems = <Widget>[];
    final ThemeData themeData = Theme.of(context);
    final TextStyle headerStyle = themeData.textTheme.body2.copyWith(color: themeData.accentColor);
    String category;
    for (GalleryItem galleryItem in kAllGalleryItems) {
      if (category != galleryItem.category) {
        if (category != null)
          listItems.add(const Divider());
        listItems.add(
          new MergeSemantics(
            child: new Container(
              height: 48.0,
              padding: const EdgeInsetsDirectional.only(start: 16.0),
              alignment: AlignmentDirectional.centerStart,
              child: new SafeArea(
                top: false,
                bottom: false,
                child: new Semantics(
                  header: true,
                  child: new Text(galleryItem.category, style: headerStyle),
                ),
              ),
            ),
          )
        );
        category = galleryItem.category;
      }
      listItems.add(galleryItem);
    }
    return listItems;
  }

  @override
  Widget build(BuildContext context) {
    Widget home = new Scaffold(
      key: _scaffoldKey,
      drawer: new GalleryDrawer(
        galleryTheme: widget.galleryTheme,
        onThemeChanged: widget.onThemeChanged,
        timeDilation: widget.timeDilation,
        onTimeDilationChanged: widget.onTimeDilationChanged,
        textScaleFactor: widget.textScaleFactor,
        onTextScaleFactorChanged: widget.onTextScaleFactorChanged,
        showPerformanceOverlay: widget.showPerformanceOverlay,
        onShowPerformanceOverlayChanged: widget.onShowPerformanceOverlayChanged,
        checkerboardRasterCacheImages: widget.checkerboardRasterCacheImages,
        onCheckerboardRasterCacheImagesChanged: widget.onCheckerboardRasterCacheImagesChanged,
        checkerboardOffscreenLayers: widget.checkerboardOffscreenLayers,
        onCheckerboardOffscreenLayersChanged: widget.onCheckerboardOffscreenLayersChanged,
        onPlatformChanged: widget.onPlatformChanged,
        overrideDirection: widget.overrideDirection,
        onOverrideDirectionChanged: widget.onOverrideDirectionChanged,
        onSendFeedback: widget.onSendFeedback,
      ),
      body: new CustomScrollView(
        slivers: <Widget>[
          const SliverAppBar(
            pinned: true,
            expandedHeight: _kFlexibleSpaceMaxHeight,
            flexibleSpace: const FlexibleSpaceBar(
              title: const Text('Flutter Gallery'),
              // TODO(abarth): Wire up to the parallax in a way that doesn't pop during hero transition.
              background: const _AppBarBackground(animation: kAlwaysDismissedAnimation),
            ),
          ),
          new SliverList(delegate: new SliverChildListDelegate(_galleryListItems())),
        ],
      )
    );

    assert(() {
      GalleryHome.showPreviewBanner = false;
      return true;
    }());

    if (GalleryHome.showPreviewBanner) {
      home = new Stack(
        fit: StackFit.expand,
        children: <Widget>[
          home,
          new FadeTransition(
            opacity: new CurvedAnimation(parent: _controller, curve: Curves.easeInOut),
            child: const Banner(
              message: 'PREVIEW',
              location: BannerLocation.topEnd,
            )
          ),
        ]
      );
    }

    return home;
  }
}