Flutter小技巧

1. 获取状态栏高度

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

2. 设置AppBar的高度

Scaffold( 
        appBar: PreferredSize(
        child: AppBar(
        ),
        preferredSize: Size.fromHeight(screenSize.height * 0.07))
);

3. 系统默认的AppBar、TabBar高度

在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;

/// The amount of time theme change animations should last.
const Duration kThemeChangeDuration = Duration(milliseconds: 200);

/// The radius of a circular material ink response in logical pixels.
const double kRadialReactionRadius = 20.0;

/// The amount of time a circular material ink response should take to expand to its full size.
const Duration kRadialReactionDuration = Duration(milliseconds: 100);

/// The value of the alpha channel to use when drawing a circular material ink response.
const int kRadialReactionAlpha = 0x1F;

/// The duration of the horizontal scroll animation that occurs when a tab is tapped.
const Duration kTabScrollDuration = Duration(milliseconds: 300);

/// The horizontal padding included by [Tab]s.
const EdgeInsets kTabLabelPadding = EdgeInsets.symmetric(horizontal: 16.0);

/// The padding added around material list items.
const EdgeInsets kMaterialListPadding = EdgeInsets.symmetric(vertical: 8.0);

4. 获取当前时间戳

/** 返回当前时间戳 */
  static int currentTimeMillis() {
    return new DateTime.now().millisecondsSinceEpoch;
  }

5. 获取控件大小和相对屏幕位置

1.首先先需要对控件进行渲染
初始化GlobalKey ：GlobalKey anchorKey = GlobalKey();

2.在需要测量的控件的下面添加key：
child: Text("点击弹出悬浮窗",
  style: TextStyle(fontSize: 20),
  key: anchorKey
),

3.获取控件的坐标：
RenderBox renderBox = anchorKey.currentContext.findRenderObject();
var offset =  renderBox.localToGlobal(Offset.zero);

控件的横坐标：offset.dx
控件的纵坐标：offset.dy

如果想获得控件正下方的坐标：
 RenderBox renderBox = anchorKey.currentContext.findRenderObject();
 var offset =  renderBox.localToGlobal(Offset(0.0, renderBox.size.height));

   控件下方的横坐标：offset.dx
   控件下方的纵坐标：offset.dy

4.获取控件的大小：
RenderBox renderBox = anchorKey.currentContext.findRenderObject();
final size = renderBox.size;