Flutter:如何创建全屏蒙版视图

import 'package:flutter/material.dart';

void main() {
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        appBar: AppBar(title: Text('Fullscreen Overlay Example')),
        body: FullscreenOverlayExample(),
      ),
    );
  }
}

class FullscreenOverlayExample extends StatefulWidget {
  @override
  _FullscreenOverlayExampleState createState() => _FullscreenOverlayExampleState();
}

class _FullscreenOverlayExampleState extends State<FullscreenOverlayExample> {
  OverlayEntry? _overlayEntry;

  void _showOverlay() {
    OverlayEntry overlayEntry = OverlayEntry(
      builder: (context) => Positioned.fill(
        child: Container(
          color: Colors.black.withOpacity(0.5),
          child: Center(
            child: CircularProgressIndicator(),
          ),
        ),
      ),
    );

    _overlayEntry = overlayEntry;
    Overlay.of(context)!.insert(overlayEntry);
  }

  void _removeOverlay() {
    _overlayEntry?.remove();
    setState(() {
      _overlayEntry = null;
    });
  }

  @override
  Widget build(BuildContext context) {
    return Center(
      child: Column(
        mainAxisAlignment: MainAxisAlignment.center,
        children: [
          ElevatedButton(
            onPressed: _showOverlay,
            child: Text('Show Overlay'),
          ),
          ElevatedButton(
            onPressed: _removeOverlay,
            child: Text('Remove Overlay'),
          ),
        ],
      ),
    );
  }
}