flutter使用笔记

## MaterialApp配置主题
```
ThemeData({
  Brightness brightness, //深色还是浅色
  MaterialColor primarySwatch, //主题颜色样本，见下面介绍
  Color primaryColor, //主色，决定导航栏颜色
  Color accentColor, //次级色，决定大多数Widget的颜色，如进度条、开关等。
  Color cardColor, //卡片颜色
  Color dividerColor, //分割线颜色
  ButtonThemeData buttonTheme, //按钮主题
  Color cursorColor, //输入框光标颜色
  Color dialogBackgroundColor,//对话框背景颜色
  String fontFamily, //文字字体
  TextTheme textTheme,// 字体主题，包括标题、body等文字样式
  IconThemeData iconTheme, // Icon的默认样式
  TargetPlatform platform, //指定平台，应用特定平台控件风格
  ...
})
 
class MyApp extends StatelessWidget {
  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'qshdapp',
      theme: ThemeData(
        primaryColor: Colors.white,
      ),
      home:
          IndexPage().buildPage(null), //MyHomePage(title: 'qshdapp Home Page'),
    );
  }
}
```

## **设置沉浸式状态栏**
```
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(
      systemNavigationBarColor: const Color(0x00000000),
      systemNavigationBarDividerColor: null,
      statusBarColor: const Color(0x00000000),
      systemNavigationBarIconBrightness: Brightness.dark,
      statusBarIconBrightness: Brightness.dark,
      statusBarBrightness: Brightness.dark,
    );
    SystemChrome.setSystemUIOverlayStyle(systemUiOverlayStyle);
  }
}
```

## **相对屏幕居中定位**

1. `Stack` 和 `Align` Widget实现绝对定位, `alignment: FractionalOffset(0.5, 0.95)`
2. `Stack` 和 `Container` Widget实现绝对定位, `alignment: FractionalOffset(0.5, 0.95)`
3. `Stack` 和 `Positioned` Widget实现绝对定位, `bottom: 40.0`, **记得在Stack里面写`alignment: Alignment.center`**

例子: 
```
        child: Stack(
          alignment: Alignment.center, // 元素没定位的x/y坐标统一定位这里
          children: <Widget>[
            Container(
              child: viewService.buildComponent("amap"),
            ),
            Container(
              alignment: FractionalOffset(0.5, 0.95),
              child: Text("111111111111111111111111111111"),
            ),
            Positioned(
              left: 640.0,
              child: Text("风刀霜剑龙卷风可视对讲焚枯食淡"),
            ),
            Positioned(
              bottom: 40.0,
              child: Center(
                child: FloatingActionButton(
                  onPressed: () {
                    dispatch(IndexActionCreator.onAction(1));
                  },
                  child: Column(
                    children: <Widget>[
                      Container(
                        height: 5.0,
                      ),
                      Icon(Icons.crop_free),
                      Text("扫码"),
                    ],
                  ),
                ),
              ),
            ),
          ],
        ),
```

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