import 'package:flutter/material.dart';
import 'dart:io';
import 'package:flutter/services.dart';

void main() {
  runApp(MyApp());
  if (Platform.isAndroid) {
// 以下两行 设置android状态栏为透明的沉浸。写在组件渲染之后，是为了在渲染后进行set赋值，覆盖状态栏，写在渲染之前MaterialApp组件会覆盖掉这个值。
    SystemUiOverlayStyle systemUiOverlayStyle =
        SystemUiOverlayStyle(statusBarColor: Colors.transparent);
    SystemChrome.setSystemUIOverlayStyle(systemUiOverlayStyle);
  }
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.red,
      ),
      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> {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
        appBar: PreferredSize(
          child: Container(
            child: AppBar(
              title: Text(widget.title),
              backgroundColor: Colors.transparent,
              elevation: 0.0,
            ),
            decoration: BoxDecoration(
              gradient: LinearGradient(
                begin: Alignment.topLeft,
                end: Alignment.bottomRight,
                colors: [
                  Colors.pinkAccent,
                  Colors.white,
                ],
              ),
            ),
          ),
          preferredSize:  Size(MediaQuery.of(context).size.width, 45),
        ),

        body: SingleChildScrollView(
          child: Column(
            children: <Widget>[
              Container(
                margin: EdgeInsets.only(top: 1200),
                child: TextField(
                  decoration: InputDecoration(
                    hintText: "输入文字",
                  ),
                ),
              ),
            ],
          ),
        ));
  }
}

经过测试,不会出现输入框的各种问题