Flutter SystemChrome_methodchannel._invokemethod (package:flutter/src/s

        SystemChrome可以为应用设置一个特定的方向去显示,当应用打开时屏幕水平或竖直显示.水平和竖直显示分别有两个方向,要么正向朝下,要么反向朝上.

       手机横向和纵向: 手机竖直放置成为纵向,水平称为横向.在以前开发的日子里,我经常把纵向和横向搞反,有时想想觉得自己也好笑.

DeviceOrientation

portraitUp 纵向(竖直)朝上
如果设备的启动画面显示纵向(竖直),需要设置启动画面属性为portraitUp. 否则设备会在使用的过程中将会顺时针方向90度旋转.

await SystemChrome.setPreferredOrientations([
    DeviceOrientation.portraitUp
  ]);

报错信息 

在main函数初始化时需要调用

WidgetsFlutterBinding.ensureInitialized();

[VERBOSE-2:ui_dart_state.cc(199)] Unhandled Exception: Null check operator used on a null value
#0      MethodChannel.binaryMessenger (package:flutter/src/services/platform_channel.dart:142:86)
#1      MethodChannel._invokeMethod (package:flutter/src/services/platform_channel.dart:148:36)
#2      OptionalMethodChannel.invokeMethod (package:flutter/src/services/platform_channel.dart:461:18)
#3      SystemChrome.setPreferredOrientations (package:flutter/src/services/system_chrome.dart:242:35)
#4      main (package:loan_app/main.dart:23:16)
#5      _runMainZoned.<anonymous closure>.<anonymous closure> (dart:ui/hooks.dart:142:25)
#6      _rootRun (dart:async/zone.dart:1354:13)
#7      _CustomZone.run (dart:async/zone.dart:1258:19)
#8      _runZoned (dart:async/zone.dart:1789:10)
#9      runZonedGuarded (dart:async/zone.dart:1777:12)
#10     _runMainZoned.<anonymous closure> (dart:ui/hooks.dart:138:5)
#11     _delayEntrypointInvocation.<anonymous closure> (dart:isolate-patch/isolate_patch.dart:283:19)

 
void main() async {
  WidgetsFlutterBinding.ensureInitialized();
  await SystemChrome.setPreferredOrientations([DeviceOrientation.portraitUp])
}

 portraitDown 纵向(竖直) 朝下 如果设备启动启动画面显示纵向(竖直) 朝上,然后翻转180度,然后纵向(竖直)朝下,点击视频链接可查看

await SystemChrome.setPreferredOrientations([
    DeviceOrientation.portraitDown,
  ]);

landscapeLeft 横向(水平)向左
portraitUp 纵向(竖直)朝上顺时针旋转90度后的结果

landscapeRight 横向(水平)向右
portraitUp 纵向(竖直)朝上逆时针旋转90度后的结果

屏幕方向集合中包含portraitUp 纵向(竖直)朝上,那么手机屏幕方向纵向(竖直)朝上

await SystemChrome.setPreferredOrientations([
    DeviceOrientation.landscapeRight,
    DeviceOrientation.landscapeLeft,
    DeviceOrientation.portraitDown,
    DeviceOrientation.portraitUp
  ]);

屏幕方向集合中不包含portraitUp 纵向(竖直)朝上,那么手机屏幕方向将集合中第一项作为屏幕方向

await SystemChrome.setPreferredOrientations([
    DeviceOrientation.landscapeRight,
    DeviceOrientation.landscapeLeft,
    DeviceOrientation.portraitDown,
  ]);

SystemUiOverlay  

top 显示顶部状态栏,隐藏底部导航栏 

await SystemChrome.setEnabledSystemUIOverlays([SystemUiOverlay.top]);

 bottom 隐藏顶部状态栏,显示底部导航栏 

await SystemChrome.setEnabledSystemUIOverlays([SystemUiOverlay.bottom]);

 隐藏状态栏和导航栏 适用于应用启动画面全屏显示

await SystemChrome.setEnabledSystemUIOverlays([]);

SystemUiOverlayStyle 

 statusBarColor

 安卓手机顶部状态栏背景颜色,适用于Android N和更高版本

SystemChrome.setSystemUIOverlayStyle(SystemUiOverlayStyle(
      statusBarIconBrightness: Brightness.dark, statusBarColor: Colors.green));

statusBarIconBrightness

安卓手机顶部状态栏图标颜色,适用于Android N和更高版本

SystemChrome.setSystemUIOverlayStyle(SystemUiOverlayStyle(
      statusBarIconBrightness: Brightness.light, statusBarColor: Colors.green));

systemNavigationBarColor
Android手机底部状态栏背景颜色

SystemChrome.setSystemUIOverlayStyle(
      SystemUiOverlayStyle(systemNavigationBarColor: Colors.green));

systemNavigationBarDividerColor

Android手机底部导航栏和应用内容中间的横线背景颜色

SystemChrome.setSystemUIOverlayStyle(SystemUiOverlayStyle(
      systemNavigationBarColor: Colors.green,
      systemNavigationBarDividerColor:Colors.red,
      systemNavigationBarIconBrightness: Brightness.dark));

systemNavigationBarIconBrightness
Android手机底部导航栏图标亮度

 SystemChrome.setSystemUIOverlayStyle(SystemUiOverlayStyle(
      systemNavigationBarColor: Colors.green,
      systemNavigationBarIconBrightness: Brightness.dark));

statusBarBrightness
IOS手机顶部状态栏亮度

SystemChrome.setSystemUIOverlayStyle(SystemUiOverlayStyle(
      statusBarBrightness:Brightness.dark));

SystemChrome.setSystemUIOverlayStyle(SystemUiOverlayStyle(
      statusBarBrightness:Brightness.dark));

 ApplicationSwitcherDescription

适用于Web开发浏览器顶部导航栏文本描述 

 @override
  Widget build(BuildContext context) {
    SystemChrome.setApplicationSwitcherDescription(
        ApplicationSwitcherDescription(
            label: '关于AppLicaionSwitcher描述', primaryColor: 0xff245679));
    return Scaffold(
        body: Container(),
        );
  }