Flutter - custom alert dialog not showing

Thorvald picture Thorvald · Nov 26, 2019 · Viewed 9.5k times · Source

I am building a custom alert dialog using flutter/Dart and a Custom Show Dialog class that I got from Github and for a reason or another the dialog is not showing.

Q: How to get the dialog to show properly?

PS resultsDialog(a,b) is being called on a button click elsewhere.

Here's my code for the Alert dialog:

Future<void> resultsDialog(String sq, String sl) async {
  BuildContext ctx;
  CustomAlertDialog dialog = new CustomAlertDialog(
    content: Material(
      type: MaterialType.card,
      child: new Container(
        margin: EdgeInsets.only(left: 26.0, right: 26.0),
        decoration: new BoxDecoration(
        shape: BoxShape.rectangle,
        color: const Color(0xFFFFFF),
        borderRadius:
          new BorderRadius.all(new Radius.circular(32.0)),
        ),
        child: new Column(
          crossAxisAlignment: CrossAxisAlignment.stretch,
          children: <Widget>[
            // dialog top
            new Expanded(
                //...
            ),
            // dialog center row
            new Expanded(
                //...
            ),
            // dialog bottom row
            new Expanded(
                //...
            ),
          ],
        ),
      ),
    ),
  );
  customShowDialog(context: ctx, child: dialog);
}

Expected result:

enter image description here

PS I got the inner rows takes care of so the problem here is only getting the dialog to show up and prevent it from being dismissed that's all

Answer

chunhunghan picture chunhunghan · Nov 27, 2019

You need to pass context from your parent widget
and in your resultsDialog add a parameter BuildContext ctx
You can copy paste run full code below

code snippet

 void _incrementCounter() {
    resultsDialog(context, "a", "b");
    setState(() {

Future<void> resultsDialog(BuildContext ctx, String sq, String sl) async {
  //BuildContext ctx;
  CustomAlertDialog dialog = new CustomAlertDialog(
    content: Material(
      type: MaterialType.card,
      child: new Container(
        margin: EdgeInsets.only(left: 26.0, right: 26.0),
        decoration: new BoxDecoration(
          shape: BoxShape.rectangle,
          color: const Color(0xFFFFFF),
          borderRadius:
          new BorderRadius.all(new Radius.circular(32.0)),
        ),
        child: new Column(
          crossAxisAlignment: CrossAxisAlignment.stretch,
          children: <Widget>[
            // dialog top
            Text('Dialog OK'),
            Text('${sq}'),
            Text('${sl}'),
          ],
        ),
      ),
    ),
  );
  customShowDialog(context: ctx, child: dialog);
}

working demo

enter image description here

full code

import 'package:flutter/material.dart';
import 'dart:async';
import 'dart:ui';

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

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(
        // This is the theme of your application.
        //
        // Try running your application with "flutter run". You'll see the
        // application has a blue toolbar. Then, without quitting the app, try
        // changing the primarySwatch below to Colors.green and then invoke
        // "hot reload" (press "r" in the console where you ran "flutter run",
        // or simply save your changes to "hot reload" in a Flutter IDE).
        // Notice that the counter didn't reset back to zero; the application
        // is not restarted.
        primarySwatch: Colors.blue,
      ),
      home: MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

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

  // This widget is the home page of your application. It is stateful, meaning
  // that it has a State object (defined below) that contains fields that affect
  // how it looks.

  // This class is the configuration for the state. It holds the values (in this
  // case the title) provided by the parent (in this case the App widget) and
  // used by the build method of the State. Fields in a Widget subclass are
  // always marked "final".

  final String title;

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

class _MyHomePageState extends State<MyHomePage> {
  int _counter = 0;

  void _incrementCounter() {
    resultsDialog(context, "a", "b");
    setState(() {
      // This call to setState tells the Flutter framework that something has
      // changed in this State, which causes it to rerun the build method below
      // so that the display can reflect the updated values. If we changed
      // _counter without calling setState(), then the build method would not be
      // called again, and so nothing would appear to happen.
      _counter++;
    });
  }

  @override
  Widget build(BuildContext context) {
    // This method is rerun every time setState is called, for instance as done
    // by the _incrementCounter method above.
    //
    // The Flutter framework has been optimized to make rerunning build methods
    // fast, so that you can just rebuild anything that needs updating rather
    // than having to individually change instances of widgets.
    return Scaffold(
      appBar: AppBar(
        // Here we take the value from the MyHomePage object that was created by
        // the App.build method, and use it to set our appbar title.
        title: Text(widget.title),
      ),
      body: Center(
        // Center is a layout widget. It takes a single child and positions it
        // in the middle of the parent.
        child: Column(
          // Column is also a layout widget. It takes a list of children and
          // arranges them vertically. By default, it sizes itself to fit its
          // children horizontally, and tries to be as tall as its parent.
          //
          // Invoke "debug painting" (press "p" in the console, choose the
          // "Toggle Debug Paint" action from the Flutter Inspector in Android
          // Studio, or the "Toggle Debug Paint" command in Visual Studio Code)
          // to see the wireframe for each widget.
          //
          // Column has various properties to control how it sizes itself and
          // how it positions its children. Here we use mainAxisAlignment to
          // center the children vertically; the main axis here is the vertical
          // axis because Columns are vertical (the cross axis would be
          // horizontal).
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            Text(
              'You have pushed the button this many times:',
            ),
            Text(
              '$_counter',
              style: Theme.of(context).textTheme.display1,
            ),
          ],
        ),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: _incrementCounter,
        tooltip: 'Increment',
        child: Icon(Icons.add),
      ), // This trailing comma makes auto-formatting nicer for build methods.
    );
  }
}

Future<void> resultsDialog(BuildContext ctx, String sq, String sl) async {
  //BuildContext ctx;
  CustomAlertDialog dialog = new CustomAlertDialog(
    content: Material(
      type: MaterialType.card,
      child: new Container(
        margin: EdgeInsets.only(left: 26.0, right: 26.0),
        decoration: new BoxDecoration(
          shape: BoxShape.rectangle,
          color: const Color(0xFFFFFF),
          borderRadius:
          new BorderRadius.all(new Radius.circular(32.0)),
        ),
        child: new Column(
          crossAxisAlignment: CrossAxisAlignment.stretch,
          children: <Widget>[
            // dialog top
            Text('Dialog OK'),
            Text('${sq}'),
            Text('${sl}'),
          ],
        ),
      ),
    ),
  );
  customShowDialog(context: ctx, child: dialog);
}

// Copyright 2015 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.



// Examples can assume:
// enum Department { treasury, state }

/// A material design dialog.
///
/// This dialog widget does not have any opinion about the contents of the
/// dialog. Rather than using this widget directly, consider using [AlertDialog]
/// or [SimpleDialog], which implement specific kinds of material design
/// dialogs.
///
/// See also:
///
///  * [AlertDialog], for dialogs that have a message and some buttons.
///  * [SimpleDialog], for dialogs that offer a variety of options.
///  * [showDialog], which actually displays the dialog and returns its result.
///  * <https://material.google.com/components/dialogs.html>
class Dialog extends StatelessWidget {
  /// Creates a dialog.
  ///
  /// Typically used in conjunction with [showDialog].
  const Dialog({
    Key key,
    this.child,
    this.insetAnimationDuration: const Duration(milliseconds: 100),
    this.insetAnimationCurve: Curves.decelerate,
  }) : super(key: key);

  /// The widget below this widget in the tree.
  ///
  /// {@macro flutter.widgets.child}
  final Widget child;

  /// The duration of the animation to show when the system keyboard intrudes
  /// into the space that the dialog is placed in.
  ///
  /// Defaults to 100 milliseconds.
  final Duration insetAnimationDuration;

  /// The curve to use for the animation shown when the system keyboard intrudes
  /// into the space that the dialog is placed in.
  ///
  /// Defaults to [Curves.fastOutSlowIn].
  final Curve insetAnimationCurve;

  Color _getColor(BuildContext context) {
    return Theme.of(context).dialogBackgroundColor;
  }

  @override
  Widget build(BuildContext context) {
    return new AnimatedPadding(
      padding: MediaQuery.of(context).viewInsets +
          const EdgeInsets.symmetric(horizontal: 40.0, vertical: 24.0),
      duration: insetAnimationDuration,
      curve: insetAnimationCurve,
      child: new MediaQuery.removeViewInsets(
        removeLeft: true,
        removeTop: true,
        removeRight: true,
        removeBottom: true,
        context: context,
        child: new Center(
          child: new ConstrainedBox(
            constraints: const BoxConstraints(minWidth: 280.0),
            child: new Material(
              borderRadius: BorderRadius.all(Radius.circular(20.0)),
              elevation: 30.0,
              color: _getColor(context),
              type: MaterialType.card,
              child: child,
            ),
          ),
        ),
      ),
    );
  }
}

/// A material design alert dialog.
///
/// An alert dialog informs the user about situations that require
/// acknowledgement. An alert dialog has an optional title and an optional list
/// of actions. The title is displayed above the content and the actions are
/// displayed below the content.
///
/// If the content is too large to fit on the screen vertically, the dialog will
/// display the title and the actions and let the content overflow. Consider
/// using a scrolling widget, such as [ListView], for [content] to avoid
/// overflow.
///
/// For dialogs that offer the user a choice between several options, consider
/// using a [SimpleDialog].
///
/// Typically passed as the child widget to [showDialog], which displays the
/// dialog.
///
/// ## Sample code
///
/// This snippet shows a method in a [State] which, when called, displays a dialog box
/// and returns a [Future] that completes when the dialog is dismissed.
///
/// ```dart
/// Future<Null> _neverSatisfied() async {
///   return showDialog<Null>(
///     context: context,
///     barrierDismissible: false, // user must tap button!
///     builder: (BuildContext context) {
///       return new AlertDialog(
///         title: new Text('Rewind and remember'),
///         content: new SingleChildScrollView(
///           child: new ListBody(
///             children: <Widget>[
///               new Text('You will never be satisfied.'),
///               new Text('You\’re like me. I’m never satisfied.'),
///             ],
///           ),
///         ),
///         actions: <Widget>[
///           new FlatButton(
///             child: new Text('Regret'),
///             onPressed: () {
///               Navigator.of(context).pop();
///             },
///           ),
///         ],
///       );
///     },
///   );
/// }
/// ```
///
/// See also:
///
///  * [SimpleDialog], which handles the scrolling of the contents but has no [actions].
///  * [Dialog], on which [AlertDialog] and [SimpleDialog] are based.
///  * [showDialog], which actually displays the dialog and returns its result.
///  * <https://material.google.com/components/dialogs.html#dialogs-alerts>
class CustomAlertDialog extends StatelessWidget {
  /// Creates an alert dialog.
  ///
  /// Typically used in conjunction with [showDialog].
  ///
  /// The [contentPadding] must not be null. The [titlePadding] defaults to
  /// null, which implies a default that depends on the values of the other
  /// properties. See the documentation of [titlePadding] for details.
  const CustomAlertDialog({
    Key key,
    this.title,
    this.titlePadding,
    this.content,
    this.contentPadding: const EdgeInsets.fromLTRB(24.0, 20.0, 24.0, 24.0),
    this.actions,
    this.semanticLabel,
  })  : assert(contentPadding != null),
        super(key: key);

  /// The (optional) title of the dialog is displayed in a large font at the top
  /// of the dialog.
  ///
  /// Typically a [Text] widget.
  final Widget title;

  /// Padding around the title.
  ///
  /// If there is no title, no padding will be provided. Otherwise, this padding
  /// is used.
  ///
  /// This property defaults to providing 24 pixels on the top, left, and right
  /// of the title. If the [content] is not null, then no bottom padding is
  /// provided (but see [contentPadding]). If it _is_ null, then an extra 20
  /// pixels of bottom padding is added to separate the [title] from the
  /// [actions].
  final EdgeInsetsGeometry titlePadding;

  /// The (optional) content of the dialog is displayed in the center of the
  /// dialog in a lighter font.
  ///
  /// Typically, this is a [ListView] containing the contents of the dialog.
  /// Using a [ListView] ensures that the contents can scroll if they are too
  /// big to fit on the display.
  final Widget content;

  /// Padding around the content.
  ///
  /// If there is no content, no padding will be provided. Otherwise, padding of
  /// 20 pixels is provided above the content to separate the content from the
  /// title, and padding of 24 pixels is provided on the left, right, and bottom
  /// to separate the content from the other edges of the dialog.
  final EdgeInsetsGeometry contentPadding;

  /// The (optional) set of actions that are displayed at the bottom of the
  /// dialog.
  ///
  /// Typically this is a list of [FlatButton] widgets.
  ///
  /// These widgets will be wrapped in a [ButtonBar], which introduces 8 pixels
  /// of padding on each side.
  ///
  /// If the [title] is not null but the [content] _is_ null, then an extra 20
  /// pixels of padding is added above the [ButtonBar] to separate the [title]
  /// from the [actions].
  final List<Widget> actions;

  /// The semantic label of the dialog used by accessibility frameworks to
  /// announce screen transitions when the dialog is opened and closed.
  ///
  /// If this label is not provided, a semantic label will be infered from the
  /// [title] if it is not null.  If there is no title, the label will be taken
  /// from [MaterialLocalizations.alertDialogLabel].
  ///
  /// See also:
  ///
  ///  * [SemanticsConfiguration.isRouteName], for a description of how this
  ///    value is used.
  final String semanticLabel;

  @override
  Widget build(BuildContext context) {
    final List<Widget> children = <Widget>[];
    String label = semanticLabel;

    if (title != null) {
      children.add(new Padding(
        padding: titlePadding ??
            new EdgeInsets.fromLTRB(
                24.0, 24.0, 24.0, content == null ? 20.0 : 0.0),
        child: new DefaultTextStyle(
          style: Theme.of(context).textTheme.title,
          child: new Semantics(child: title, namesRoute: true),
        ),
      ));
    } else {
      switch (defaultTargetPlatform) {
        case TargetPlatform.iOS:
          label = semanticLabel;
          break;
        case TargetPlatform.android:
        case TargetPlatform.fuchsia:
          label = semanticLabel ??
              MaterialLocalizations.of(context)?.alertDialogLabel;
      }
    }

    if (content != null) {
      children.add(new Flexible(
        child: new Padding(
          padding: contentPadding,
          child: new DefaultTextStyle(
            style: Theme.of(context).textTheme.subhead,
            child: content,
          ),
        ),
      ));
    }

    if (actions != null) {
      children.add(new ButtonTheme.bar(
        child: new ButtonBar(
          children: actions,
        ),
      ));
    }

    Widget dialogChild = new IntrinsicWidth(
      child: new Column(
        mainAxisSize: MainAxisSize.min,
        crossAxisAlignment: CrossAxisAlignment.stretch,
        children: children,
      ),
    );

    if (label != null)
      dialogChild =
      new Semantics(namesRoute: true, label: label, child: dialogChild);

    return new Dialog(child: dialogChild);
  }
}

/// An option used in a [SimpleDialog].
///
/// A simple dialog offers the user a choice between several options. This
/// widget is commonly used to represent each of the options. If the user
/// selects this option, the widget will call the [onPressed] callback, which
/// typically uses [Navigator.pop] to close the dialog.
///
/// The padding on a [SimpleDialogOption] is configured to combine with the
/// default [SimpleDialog.contentPadding] so that each option ends up 8 pixels
/// from the other vertically, with 20 pixels of spacing between the dialog's
/// title and the first option, and 24 pixels of spacing between the last option
/// and the bottom of the dialog.
///
/// ## Sample code
///
/// ```dart
/// new SimpleDialogOption(
///   onPressed: () { Navigator.pop(context, Department.treasury); },
///   child: const Text('Treasury department'),
/// )
/// ```
///
/// See also:
///
///  * [SimpleDialog], for a dialog in which to use this widget.
///  * [showDialog], which actually displays the dialog and returns its result.
///  * [FlatButton], which are commonly used as actions in other kinds of
///    dialogs, such as [AlertDialog]s.
///  * <https://material.google.com/components/dialogs.html#dialogs-simple-dialogs>
class SimpleDialogOption extends StatelessWidget {
  /// Creates an option for a [SimpleDialog].
  const SimpleDialogOption({
    Key key,
    this.onPressed,
    this.child,
  }) : super(key: key);

  /// The callback that is called when this option is selected.
  ///
  /// If this is set to null, the option cannot be selected.
  ///
  /// When used in a [SimpleDialog], this will typically call [Navigator.pop]
  /// with a value for [showDialog] to complete its future with.
  final VoidCallback onPressed;

  /// The widget below this widget in the tree.
  ///
  /// Typically a [Text] widget.
  final Widget child;

  @override
  Widget build(BuildContext context) {
    return new InkWell(
      onTap: onPressed,
      child: new Padding(
          padding: const EdgeInsets.symmetric(vertical: 8.0, horizontal: 24.0),
          child: child),
    );
  }
}

/// A simple material design dialog.
///
/// A simple dialog offers the user a choice between several options. A simple
/// dialog has an optional title that is displayed above the choices.
///
/// Choices are normally represented using [SimpleDialogOption] widgets. If
/// other widgets are used, see [contentPadding] for notes regarding the
/// conventions for obtaining the spacing expected by Material Design.
///
/// For dialogs that inform the user about a situation, consider using an
/// [AlertDialog].
///
/// Typically passed as the child widget to [showDialog], which displays the
/// dialog.
///
/// ## Sample code
///
/// In this example, the user is asked to select between two options. These
/// options are represented as an enum. The [showDialog] method here returns
/// a [Future] that completes to a value of that enum. If the user cancels
/// the dialog (e.g. by hitting the back button on Android, or tapping on the
/// mask behind the dialog) then the future completes with the null value.
///
/// The return value in this example is used as the index for a switch statement.
/// One advantage of using an enum as the return value and then using that to
/// drive a switch statement is that the analyzer will flag any switch statement
/// that doesn't mention every value in the enum.
///
/// ```dart
/// Future<Null> _askedToLead() async {
///   switch (await showDialog<Department>(
///     context: context,
///     builder: (BuildContext context) {
///       return new SimpleDialog(
///         title: const Text('Select assignment'),
///         children: <Widget>[
///           new SimpleDialogOption(
///             onPressed: () { Navigator.pop(context, Department.treasury); },
///             child: const Text('Treasury department'),
///           ),
///           new SimpleDialogOption(
///             onPressed: () { Navigator.pop(context, Department.state); },
///             child: const Text('State department'),
///           ),
///         ],
///       );
///     }
///   )) {
///     case Department.treasury:
///       // Let's go.
///       // ...
///     break;
///     case Department.state:
///       // ...
///     break;
///   }
/// }
/// ```
///
/// See also:
///
///  * [SimpleDialogOption], which are options used in this type of dialog.
///  * [AlertDialog], for dialogs that have a row of buttons below the body.
///  * [Dialog], on which [SimpleDialog] and [AlertDialog] are based.
///  * [showDialog], which actually displays the dialog and returns its result.
///  * <https://material.google.com/components/dialogs.html#dialogs-simple-dialogs>
class SimpleDialog extends StatelessWidget {
  /// Creates a simple dialog.
  ///
  /// Typically used in conjunction with [showDialog].
  ///
  /// The [titlePadding] and [contentPadding] arguments must not be null.
  const SimpleDialog({
    Key key,
    this.title,
    this.titlePadding: const EdgeInsets.fromLTRB(24.0, 24.0, 24.0, 0.0),
    this.children,
    this.contentPadding: const EdgeInsets.fromLTRB(0.0, 12.0, 0.0, 16.0),
    this.semanticLabel,
  })  : assert(titlePadding != null),
        assert(contentPadding != null),
        super(key: key);

  /// The (optional) title of the dialog is displayed in a large font at the top
  /// of the dialog.
  ///
  /// Typically a [Text] widget.
  final Widget title;

  /// Padding around the title.
  ///
  /// If there is no title, no padding will be provided.
  ///
  /// By default, this provides the recommend Material Design padding of 24
  /// pixels around the left, top, and right edges of the title.
  ///
  /// See [contentPadding] for the conventions regarding padding between the
  /// [title] and the [children].
  final EdgeInsetsGeometry titlePadding;

  /// The (optional) content of the dialog is displayed in a
  /// [SingleChildScrollView] underneath the title.
  ///
  /// Typically a list of [SimpleDialogOption]s.
  final List<Widget> children;

  /// Padding around the content.
  ///
  /// By default, this is 12 pixels on the top and 16 pixels on the bottom. This
  /// is intended to be combined with children that have 24 pixels of padding on
  /// the left and right, and 8 pixels of padding on the top and bottom, so that
  /// the content ends up being indented 20 pixels from the title, 24 pixels
  /// from the bottom, and 24 pixels from the sides.
  ///
  /// The [SimpleDialogOption] widget uses such padding.
  ///
  /// If there is no [title], the [contentPadding] should be adjusted so that
  /// the top padding ends up being 24 pixels.
  final EdgeInsetsGeometry contentPadding;

  /// The semantic label of the dialog used by accessibility frameworks to
  /// announce screen transitions when the dialog is opened and closed.
  ///
  /// If this label is not provided, a semantic label will be infered from the
  /// [title] if it is not null.  If there is no title, the label will be taken
  /// from [MaterialLocalizations.dialogLabel].
  ///
  /// See also:
  ///
  ///  * [SemanticsConfiguration.isRouteName], for a description of how this
  ///    value is used.
  final String semanticLabel;

  @override
  Widget build(BuildContext context) {
    final List<Widget> body = <Widget>[];
    String label = semanticLabel;

    if (title != null) {
      body.add(new Padding(
          padding: titlePadding,
          child: new DefaultTextStyle(
            style: Theme.of(context).textTheme.title,
            child: new Semantics(namesRoute: true, child: title),
          )));
    } else {
      switch (defaultTargetPlatform) {
        case TargetPlatform.iOS:
          label = semanticLabel;
          break;
        case TargetPlatform.android:
        case TargetPlatform.fuchsia:
          label =
              semanticLabel ?? MaterialLocalizations.of(context)?.dialogLabel;
      }
    }

    if (children != null) {
      body.add(new Flexible(
          child: new SingleChildScrollView(
            padding: contentPadding,
            child: new ListBody(children: children),
          )));
    }

    Widget dialogChild = new IntrinsicWidth(
      stepWidth: 56.0,
      child: new ConstrainedBox(
        constraints: const BoxConstraints(minWidth: 280.0),
        child: new Column(
          mainAxisSize: MainAxisSize.min,
          crossAxisAlignment: CrossAxisAlignment.stretch,
          children: body,
        ),
      ),
    );

    if (label != null)
      dialogChild = new Semantics(
        namesRoute: true,
        label: label,
        child: dialogChild,
      );
    return new Dialog(child: dialogChild);
  }
}

class _DialogRoute<T> extends PopupRoute<T> {
  _DialogRoute({
    @required this.theme,
    bool barrierDismissible: true,
    this.barrierLabel,
    @required this.child,
    RouteSettings settings,
  })  : assert(barrierDismissible != null),
        _barrierDismissible = barrierDismissible,
        super(settings: settings);

  final Widget child;
  final ThemeData theme;

  @override
  Duration get transitionDuration => const Duration(milliseconds: 150);

  @override
  bool get barrierDismissible => _barrierDismissible;
  final bool _barrierDismissible;

  @override
  Color get barrierColor => Colors.black54;

  @override
  final String barrierLabel;

  @override
  Widget buildPage(BuildContext context, Animation<double> animation,
      Animation<double> secondaryAnimation) {
    return new SafeArea(
      child: new Builder(builder: (BuildContext context) {
        final Widget annotatedChild = new Semantics(
          child: child,
          scopesRoute: true,
          explicitChildNodes: true,
        );
        return theme != null
            ? new Theme(data: theme, child: annotatedChild)
            : annotatedChild;
      }),
    );
  }

  @override
  Widget buildTransitions(BuildContext context, Animation<double> animation,
      Animation<double> secondaryAnimation, Widget child) {
    return new FadeTransition(
        opacity: new CurvedAnimation(parent: animation, curve: Curves.easeOut),
        child: child);
  }
}

/// Displays a dialog above the current contents of the app.
///
/// This function takes a `builder` which typically builds a [Dialog] widget.
/// Content below the dialog is dimmed with a [ModalBarrier]. This widget does
/// not share a context with the location that `showDialog` is originally
/// called from. Use a [StatefulBuilder] or a custom [StatefulWidget] if the
/// dialog needs to update dynamically.
///
/// The `context` argument is used to look up the [Navigator] and [Theme] for
/// the dialog. It is only used when the method is called. Its corresponding
/// widget can be safely removed from the tree before the dialog is closed.
///
/// The `child` argument is deprecated, and should be replaced with `builder`.
///
/// Returns a [Future] that resolves to the value (if any) that was passed to
/// [Navigator.pop] when the dialog was closed.
///
/// The dialog route created by this method is pushed to the root navigator.
/// If the application has multiple [Navigator] objects, it may be necessary to
/// call `Navigator.of(context, rootNavigator: true).pop(result)` to close the
/// dialog rather just 'Navigator.pop(context, result)`.
///
/// See also:
///  * [AlertDialog], for dialogs that have a row of buttons below a body.
///  * [SimpleDialog], which handles the scrolling of the contents and does
///    not show buttons below its body.
///  * [Dialog], on which [SimpleDialog] and [AlertDialog] are based.
///  * <https://material.google.com/components/dialogs.html>
Future<T> customShowDialog<T>({
  @required
  BuildContext context,
  bool barrierDismissible: true,
  @Deprecated(
      'Instead of using the "child" argument, return the child from a closure '
          'provided to the "builder" argument. This will ensure that the BuildContext '
          'is appropriate for widgets built in the dialog.')
  Widget child,
  WidgetBuilder builder,
}) {
  assert(child == null || builder == null);
  return Navigator.of(context, rootNavigator: true).push(new _DialogRoute<T>(
    child: child ?? new Builder(builder: builder),
    theme: Theme.of(context, shadowThemeOnly: true),
    barrierDismissible: barrierDismissible,
    barrierLabel:
    MaterialLocalizations.of(context).modalBarrierDismissLabel,
  ));
}