Flutter - 自定义警报对话框未显示

Question

我正在 build 一个 custom alert dialog使用 flutter/Dart 和 Custom Show Dialog我从 Github 获得的类(class)，出于某种原因，对话框没有显示。

问:如何让对话框正确显示？

PS resultsDialog(a,b)在别处单击按钮时被调用。

这是我的警报对话框代码:

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);
}

预期结果:



PS 我得到了内部行的照顾，所以这里的问题只是让对话框出现并防止它被关闭

Answer 1

您需要从父小部件传递上下文
并在您的 resultsDialog添加参数 BuildContext ctx您可以在下面复制粘贴运行完整代码

代码片段

 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);
}

工作演示



完整代码

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,
  ));
}