简介

Scaffold是一个Flutter小部件，用于定义应用程序的基本布局元素，例如应用程序栏、抽屉式菜单、底部导航栏和浮动操作按钮等。它是一个方便的小部件，可以帮助您快速构建具有常见应用程序组件的布局。

常用重要属性

Scaffold小部件通常包含以下元素：

AppBar：位于页面顶部，通常用于显示应用程序名称、菜单按钮、搜索框或其他重要控件。

BottomNavigationBar：位于页面底部，通常用于允许用户切换不同的页面或功能。

Drawer：可从屏幕左侧滑动出现的侧边栏，通常用于显示应用程序的导航菜单或其他重要信息。

FloatingActionButton：一个浮动的圆形按钮，通常用于触发最常用的操作。

body：通常是应用程序中最重要的部分，它包含应用程序的实际内容，例如列表、表单、图像或其他小部件。

一个简单例子

下面是一个简单的示例，演示如何使用Scaffold来创建一个包含AppBar和body的基本布局：

import 'package:flutter/material.dart';
void main() => runApp(MyApp());
class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'My App',
      home: Scaffold(
        appBar: AppBar(
          title: Text('My App'),
        ),
        body: Center(
          child: Text('Hello World!'),
        ),
      ),
    );
  }
}

在这个例子中，我们创建了一个名为MyApp的Flutter应用程序。我们使用Scaffold小部件作为home属性的值，来定义应用程序的基本布局。我们设置了应用程序栏的标题为My App，并将页面的主体设置为一个居中对齐的文本小部件，显示Hello World!。

总之，Scaffold是一个非常有用的小部件，它可以让您快速构建具有常见应用程序组件的布局。它还提供了许多自定义选项，可以让您根据需要修改应用程序的外观和行为。

Scaffold包括的属性

const Scaffold(
{Key? key,
PreferredSizeWidget? appBar,
Widget? body,
Widget? floatingActionButton,
FloatingActionButtonLocation? floatingActionButtonLocation,
FloatingActionButtonAnimator? floatingActionButtonAnimator,
List<Widget>? persistentFooterButtons,
AlignmentDirectional persistentFooterAlignment = AlignmentDirectional.centerEnd,
Widget? drawer,
DrawerCallback? onDrawerChanged,
Widget? endDrawer,
DrawerCallback? onEndDrawerChanged,
Widget? bottomNavigationBar,
Widget? bottomSheet,
Color? backgroundColor,
bool? resizeToAvoidBottomInset,
bool primary = true,
DragStartBehavior drawerDragStartBehavior = DragStartBehavior.start,
bool extendBody = false,
bool extendBodyBehindAppBar = false,
Color? drawerScrimColor,
double? drawerEdgeDragWidth,
bool drawerEnableOpenDragGesture = true,
bool endDrawerEnableOpenDragGesture = true,
String? restorationId}
)

属性的解释

appBar → PreferredSizeWidget?

An app bar to display at the top of the scaffold.

final

backgroundColor → Color?

The color of the Material widget that underlies the entire Scaffold.

final

body → Widget?

The primary content of the scaffold.

final

bottomNavigationBar → Widget?

A bottom navigation bar to display at the bottom of the scaffold.

final

bottomSheet → Widget?

The persistent bottom sheet to display.

final

drawer → Widget?

A panel displayed to the side of the body, often hidden on mobile devices. Swipes in from either left-to-right (TextDirection.ltr) or right-to-left (TextDirection.rtl)

final

drawerDragStartBehavior → DragStartBehavior

Determines the way that drag start behavior is handled.

final

drawerEdgeDragWidth → double?

The width of the area within which a horizontal swipe will open the drawer.

final

drawerEnableOpenDragGesture → bool

Determines if the Scaffold.drawer can be opened with a drag gesture on mobile.

final

drawerScrimColor → Color?

The color to use for the scrim that obscures primary content while a drawer is open.

final

endDrawer → Widget?

A panel displayed to the side of the body, often hidden on mobile devices. Swipes in from right-to-left (TextDirection.ltr) or left-to-right (TextDirection.rtl)

final

endDrawerEnableOpenDragGesture → bool

Determines if the Scaffold.endDrawer can be opened with a gesture on mobile.

final

extendBody → bool

If true, and bottomNavigationBar or persistentFooterButtons is specified, then the body extends to the bottom of the Scaffold, instead of only extending to the top of the bottomNavigationBar or the persistentFooterButtons.

final

extendBodyBehindAppBar → bool

If true, and an appBar is specified, then the height of the body is extended to include the height of the app bar and the top of the body is aligned with the top of the app bar.

final

floatingActionButton → Widget?

A button displayed floating above body, in the bottom right corner.

final

floatingActionButtonAnimator → FloatingActionButtonAnimator?

Animator to move the floatingActionButton to a new floatingActionButtonLocation.

final

floatingActionButtonLocation → FloatingActionButtonLocation?

Responsible for determining where the floatingActionButton should go.

final

hashCode → int

The hash code for this object.

@nonVirtual, read-only, inherited

key → Key?

Controls how one widget replaces another widget in the tree.

final, inherited

onDrawerChanged → DrawerCallback?

Optional callback that is called when the Scaffold.drawer is opened or closed.

final

onEndDrawerChanged → DrawerCallback?

Optional callback that is called when the Scaffold.endDrawer is opened or closed.

final

persistentFooterAlignment → AlignmentDirectional

The alignment of the persistentFooterButtons inside the OverflowBar.

final

persistentFooterButtons → List<Widget>?

A set of buttons that are displayed at the bottom of the scaffold.

final

primary → bool

Whether this scaffold is being displayed at the top of the screen.

final

resizeToAvoidBottomInset → bool?

If true the body and the scaffold’s floating widgets should size themselves to avoid the onscreen keyboard whose height is defined by the ambient MediaQuery’s MediaQueryData.viewInsets bottom property.

final

restorationId → String?

Restoration ID to save and restore the state of the Scaffold.

final

runtimeType → Type

A representation of the runtime type of the object.

read-only, inherited

使用

见下面的例子

 Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text("WhatsApp"),
        elevation: 0.7,
        bottom: TabBar(
          controller: _tabController,
          indicatorColor: Colors.blue,
          tabs: <Widget>[
            Tab(icon: Icon(Icons.camera_alt)),
            Tab(text: "CHATS"),
            Tab(text: "STATUS"),
            Tab(text: "CALLS"),
          ],
        ),
        actions: <Widget>[
          Icon(Icons.search),
          Padding(
            padding: const EdgeInsets.symmetric(horizontal: 5.0),
          ),
          Icon(Icons.more_vert)
        ],
      ),
      body: TabBarView(
        controller: _tabController,
        children: <Widget>[
          CameraScreen(widget.cameras),
          ChatScreen(),
          StatusScreen(),
          CallsScreen(),
        ],
      ),
      floatingActionButton: showFab
          ? FloatingActionButton(
              backgroundColor: Theme.of(context).accentColor,
              child: Icon(
                Icons.add,
                color: Colors.white,
              ),
              onPressed: () => debugDumpApp(),
            )
          : null,
      bottomNavigationBar: BottomNavigationBar(
        items: const <BottomNavigationBarItem>[
          BottomNavigationBarItem(
            icon: Icon(Icons.home),
            label: 'Home',
          ),
          BottomNavigationBarItem(
            icon: Icon(Icons.business),
            label: 'Business',
          ),
          BottomNavigationBarItem(
            icon: Icon(Icons.school),
            label: 'School',
          ),
        ],
        // currentIndex: _selectedIndex,
        selectedItemColor: Colors.amber[800],
        onTap: _onItemTapped,
      ),
    );
  }

上述代码运行起来的效果如下：