How to animate Alert dialog position in Flutter?

Screenshot:

---

Code:

floatingActionButton: FloatingActionButton(
  onPressed: () {
    showGeneralDialog(
      barrierLabel: "Label",
      barrierDismissible: true,
      barrierColor: Colors.black.withOpacity(0.5),
      transitionDuration: Duration(milliseconds: 700),
      context: context,
      pageBuilder: (context, anim1, anim2) {
        return Align(
          alignment: Alignment.bottomCenter,
          child: Container(
            height: 300,
            child: SizedBox.expand(child: FlutterLogo()),
            margin: EdgeInsets.only(bottom: 50, left: 12, right: 12),
            decoration: BoxDecoration(
              color: Colors.white,
              borderRadius: BorderRadius.circular(40),
            ),
          ),
        );
      },
      transitionBuilder: (context, anim1, anim2, child) {
        return SlideTransition(
          position: Tween(begin: Offset(0, 1), end: Offset(0, 0)).animate(anim1),
          child: child,
        );
      },
    );
  },
)

From top to bottom you can use

bool _fromTop = true;

@override
Widget build(BuildContext context) {
  return Scaffold(
    floatingActionButton: FloatingActionButton(
      onPressed: () {
        showGeneralDialog(
          barrierLabel: "Label",
          barrierDismissible: true,
          barrierColor: Colors.black.withOpacity(0.5),
          transitionDuration: Duration(milliseconds: 700),
          context: context,
          pageBuilder: (context, anim1, anim2) {
            return Align(
              alignment: _fromTop ? Alignment.topCenter : Alignment.bottomCenter,
              child: Container(
                height: 300,
                child: SizedBox.expand(child: FlutterLogo()),
                margin: EdgeInsets.only(top: 50, left: 12, right: 12, bottom: 50),
                decoration: BoxDecoration(
                  color: Colors.white,
                  borderRadius: BorderRadius.circular(40),
                ),
              ),
            );
          },
          transitionBuilder: (context, anim1, anim2, child) {
            return SlideTransition(
              position: Tween(begin: Offset(0, _fromTop ? -1 : 1), end: Offset(0, 0)).animate(anim1),
              child: child,
            );
          },
        );
      },
    ),
  );
}

Output:

Not sure if I got your question clearly, if this is what you are looking for, replace your PopUp class with mine.

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

class MyApp extends StatelessWidget {
  // This widget is the root of your application.
  @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> {
  void showPopup() {
    showDialog(
      context: context,
      builder: (_) => PopUp(),
    );
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            Text(
              'You have pushed the button this many times:',
            ),
          ],
        ),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: showPopup,
        tooltip: 'Increment',
        child: Icon(Icons.add),
      ), // This trailing comma makes auto-formatting nicer for build methods.
    );
  }
}

class PopUp extends StatefulWidget {
  @override
  State<StatefulWidget> createState() => PopUpState();
}

class PopUpState extends State<PopUp> with TickerProviderStateMixin {
  AnimationController controller;
  double _bottom = 0, _fromTop = 300, _screenHeight, _containerHeight = 300;

  @override
  void initState() {
    super.initState();
    controller = AnimationController(duration: const Duration(milliseconds: 300), vsync: this)
      ..addListener(() {
        Timer.periodic(Duration(milliseconds: 15), (timer) {
          if (_bottom < _screenHeight - _fromTop - _containerHeight) {
            _bottom += 1;
            setState(() {});
          }
        });
      });
    controller.forward();
  }

  @override
  Widget build(BuildContext context) {
    _screenHeight = MediaQuery.of(context).size.height;
    return SizedBox(
      width: double.infinity,
      height: double.infinity,
      child: Stack(
        children: <Widget>[
          Positioned(
            bottom: _bottom,
            left: 0,
            right: 0,
            child: Container(height: _containerHeight, color: Colors.green),
          ),
        ],
      ),
    );
  }

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

import 'package:flutter/material.dart';

void main() {
  runApp(const MaterialApp(home: CityPage()));
}

class CityPage extends StatelessWidget {
  const CityPage({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Column(
        mainAxisAlignment: MainAxisAlignment.center,
        children: [
          Center(
            child: TextButton(
              child: const Text('Press me'),
              onPressed: () => BottomDialog().showBottomDialog(context),
            ),
          ),
        ],
      ),
    );
  }
}

class BottomDialog {
  void showBottomDialog(BuildContext context) {
    showGeneralDialog(
      barrierLabel: "showGeneralDialog",
      barrierDismissible: true,
      barrierColor: Colors.black.withOpacity(0.6),
      transitionDuration: const Duration(milliseconds: 400),
      context: context,
      pageBuilder: (context, _, __) {
        return Align(
          alignment: Alignment.bottomCenter,
          child: _buildDialogContent(),
        );
      },
      transitionBuilder: (_, animation1, __, child) {
        return SlideTransition(
          position: Tween(
            begin: const Offset(0, 1),
            end: const Offset(0, 0),
          ).animate(animation1),
          child: child,
        );
      },
    );
  }

  Widget _buildDialogContent() {
    return IntrinsicHeight(
      child: Container(
        width: double.maxFinite,
        clipBehavior: Clip.antiAlias,
        padding: const EdgeInsets.all(16),
        decoration: const BoxDecoration(
          color: Colors.white,
          borderRadius: BorderRadius.only(
            topLeft: Radius.circular(16),
            topRight: Radius.circular(16),
          ),
        ),
        child: Material(
          child: Column(
            children: [
              const SizedBox(height: 16),
              _buildImage(),
              const SizedBox(height: 8),
              _buildContinueText(),
              const SizedBox(height: 16),
              _buildEmapleText(),
              const SizedBox(height: 16),
              _buildTextField(),
              const SizedBox(height: 16),
              _buildContinueButton(),
            ],
          ),
        ),
      ),
    );
  }

  Widget _buildImage() {
    const image =
        'https://user-images.githubusercontent.com/47568606/134579553-da578a80-b842-4ab9-ab0b-41f945fbc2a7.png';
    return SizedBox(
      height: 88,
      child: Image.network(image, fit: BoxFit.cover),
    );
  }

  Widget _buildContinueText() {
    return const Text(
      'Continue with account',
      style: TextStyle(
        fontSize: 22,
        fontWeight: FontWeight.w500,
      ),
    );
  }

  Widget _buildEmapleText() {
    return const Text(
      'example.com',
      style: TextStyle(
        fontSize: 16,
        fontWeight: FontWeight.w500,
      ),
    );
  }

  Widget _buildTextField() {
    const iconSize = 40.0;
    return Container(
      height: 60,
      padding: const EdgeInsets.symmetric(horizontal: 16),
      decoration: BoxDecoration(
        color: Colors.white,
        border: Border.all(width: 1, color: Colors.grey.withOpacity(0.4)),
        borderRadius: const BorderRadius.all(Radius.circular(8)),
      ),
      child: Row(
        children: [
          Container(
            width: iconSize,
            height: iconSize,
            decoration: BoxDecoration(
              shape: BoxShape.circle,
              color: Colors.grey[200],
            ),
            child: const Center(
              child: Text('Е'),
            ),
          ),
          const SizedBox(height: 16),
          Column(
            mainAxisAlignment: MainAxisAlignment.spaceEvenly,
            crossAxisAlignment: CrossAxisAlignment.start,
            children: const [
              Text(
                '[email protected]',
                style: TextStyle(
                  fontWeight: FontWeight.w600,
                ),
              ),
              Text('**********'),
            ],
          )
        ],
      ),
    );
  }

  Widget _buildContinueButton() {
    return Container(
      height: 40,
      width: double.maxFinite,
      decoration: const BoxDecoration(
        color: Color(0xFF3375e0),
        borderRadius: BorderRadius.all(Radius.circular(8)),
      ),
      child: RawMaterialButton(
        onPressed: () {
          Navigator.of(context, rootNavigator: true).pop();
        },
        child: const Center(
          child: Text(
            'Continue',
            style: TextStyle(
              color: Colors.white,
              fontWeight: FontWeight.w500,
            ),
          ),
        ),
      ),
    );
  }
}