how to make profile appbar like telegram in flutter?

Question

Since i am new to flutter i want the complete implementation of this animation.

Answer 1

This is exact implementation of this AppBar:

class TransitionAppBar extends StatelessWidget {
  TransitionAppBar({
    required this.avatar,
    required this.title,
    this.extent = 250,
    Key? key,
  }) : super(key: key);

  final Widget avatar;
  final double extent;
  final String title;

  @override
  Widget build(BuildContext context) {
    return SliverPersistentHeader(
      pinned: true,
      delegate: _TransitionAppBarDelegate(
        avatar: avatar,
        title: title,
        extent: extent > 200 ? extent : 200,
      ),
    );
  }
}

class _TransitionAppBarDelegate extends SliverPersistentHeaderDelegate {
  _TransitionAppBarDelegate({required this.avatar, required this.title, this.extent = 250})
      : assert(extent >= 200, '');

  final Widget avatar;
  final double extent;
  final String title;

  final _avatarAlignTween = AlignmentTween(begin: Alignment.bottomCenter, end: Alignment.topLeft);
  final _avatarMarginTween = EdgeInsetsTween(
    end: EdgeInsets.only(left: 14, top: 36),
  );

  final _iconAlignTween = AlignmentTween(begin: Alignment.bottomRight, end: Alignment.topRight);
  final _titleMarginTween = EdgeInsetsTween(
    begin: EdgeInsets.only(bottom: 20),
    end: EdgeInsets.only(left: 64, top: 45),
  );

  @override
  double get maxExtent => extent;

  @override
  double get minExtent => 80;

  @override
  bool shouldRebuild(_TransitionAppBarDelegate oldDelegate) {
    return avatar != oldDelegate.avatar || title != oldDelegate.title;
  }

  @override
  Widget build(
    BuildContext context,
    double shrinkOffset,
    bool overlapsContent,
  ) {
    final tempVal = maxExtent * 72 / 100;
    final progress = shrinkOffset > tempVal ? 1.0 : shrinkOffset / tempVal;
    final avatarMargin = _avatarMarginTween.lerp(progress);
    final titleMargin = _titleMarginTween.lerp(progress);

    final avatarAlign = _avatarAlignTween.lerp(progress);
    final iconAlign = _iconAlignTween.lerp(progress);

    final avatarSize = (1 - progress) * 200 + 32;

    return Stack(
      children: <Widget>[
        AnimatedContainer(
          duration: Duration(milliseconds: 100),
          height: 80,
          constraints: BoxConstraints(maxHeight: minExtent),
          color: Colors.white,
        ),
        Padding(
          padding: avatarMargin,
          child: Align(
            alignment: avatarAlign,
            child: SizedBox(
              height: avatarSize,
              width: avatarSize,
              child: avatar,
            ),
          ),
        ),
        Align(
          alignment: Alignment.bottomRight,
          child: Container(
            height: progress < 0.4 ? 100 * (1 - progress) * 1.5 : 0,
            decoration: BoxDecoration(
              gradient: LinearGradient(
                begin: Alignment.topCenter,
                end: Alignment.bottomCenter,
                colors: [
                  Colors.pink[200]!.withOpacity(0.05),
                  Colors.pink[400]!.withOpacity(0.8),
                ],
              ),
            ),
          ),
        ),
        Padding(
          padding: titleMargin,
          child: Align(
            alignment: avatarAlign,
            child: Text(
              title,
            ),
          ),
        ),
        Padding(
          padding: titleMargin,
          child: Align(
            alignment: iconAlign,
            child: Padding(
              padding: const EdgeInsets.only(right: 16),
              child: GestureDetector(
                onTap: () {},
                child: Icon(
                  Icons.search,
                  size: 30,
                  color: progress < 0.4 ? Colors.white : Colors.black,
                ),
              ),
            ),
          ),
        ),
      ],
    );
  }
}

Also this answer might be helpful

Answer 2

/// Flutter code sample for SliverAppBar

// This sample shows a [SliverAppBar] and it's behavior when using the
// [pinned], [snap] and [floating] parameters.

import 'package:flutter/material.dart';

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

/// This is the main application widget.
class MyApp extends StatelessWidget {
  static const String _title = 'Flutter Code Sample';

  @override
  Widget build(BuildContext context) {
    return const MaterialApp(
      title: _title,
      home: MyStatefulWidget(),
    );
  }
}

/// This is the stateful widget that the main application instantiates.
class MyStatefulWidget extends StatefulWidget {
  const MyStatefulWidget();

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

/// This is the private State class that goes with MyStatefulWidget.
class _MyStatefulWidgetState extends State<MyStatefulWidget> {
  bool _pinned = true;
  bool _snap = false;
  bool _floating = false;

// [SliverAppBar]s are typically used in [CustomScrollView.slivers], which in
// turn can be placed in a [Scaffold.body].
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: CustomScrollView(
        slivers: <Widget>[
          SliverAppBar(
            pinned: _pinned,
            snap: _snap,
            floating: _floating,
            expandedHeight: 160.0,
            flexibleSpace: const FlexibleSpaceBar(
              title: Text('SliverAppBar'),
              background: FlutterLogo(),
            ),
          ),
          const SliverToBoxAdapter(
            child: SizedBox(
              height: 20,
              child: Center(
                child: Text('Scroll to see the SliverAppBar in effect.'),
              ),
            ),
          ),
          SliverList(
            delegate: SliverChildBuilderDelegate(
              (BuildContext context, int index) {
                return Container(
                  color: index.isOdd ? Colors.white : Colors.black12,
                  height: 100.0,
                  child: Center(
                    child: Text('$index', textScaleFactor: 5),
                  ),
                );
              },
              childCount: 20,
            ),
          ),
        ],
      ),
      bottomNavigationBar: BottomAppBar(
        child: ButtonBar(
          alignment: MainAxisAlignment.spaceEvenly,
          children: <Widget>[
            Row(
              children: <Widget>[
                const Text('pinned'),
                Switch(
                  onChanged: (bool val) {
                    setState(() {
                      _pinned = val;
                    });
                  },
                  value: _pinned,
                ),
              ],
            ),
            Row(
              children: <Widget>[
                const Text('snap'),
                Switch(
                  onChanged: (bool val) {
                    setState(() {
                      _snap = val;
                      // Snapping only applies when the app bar is floating.
                      _floating = _floating || _snap;
                    });
                  },
                  value: _snap,
                ),
              ],
            ),
            Row(
              children: <Widget>[
                const Text('floating'),
                Switch(
                  onChanged: (bool val) {
                    setState(() {
                      _floating = val;
                      _snap = _snap && _floating;
                    });
                  },
                  value: _floating,
                ),
              ],
            ),
          ],
        ),
      ),
    );
  }
}

Source - https://api.flutter.dev/flutter/material/SliverAppBar-class.html