获取状态栏高度

import 'dart:ui';
MediaQueryData.fromWindow(window).padding.top

系统默认的appBar等高度

位于Dart Packages/flutter/src/material/constans.dart

/// The height of the toolbar component of the [AppBar].
const double kToolbarHeight = 56.0;

/// The height of the bottom navigation bar.
const double kBottomNavigationBarHeight = 56.0;

/// The height of a tab bar containing text.
const double kTextTabBarHeight = 48.0;