在屏幕上添加一个 Drawer

Directions
步骤
1. Create a Scaffold
1. 创建一个 Scaffold
2. Add a drawer
2. 添加一个 drawer
3. Populate the drawer with items
3. 向 drawer 中添加内容
4. Close the drawer programmatically
4. 通过编程关闭 drawer
Interactive example
交互式样例

在 Material Design 设计准则里，主要提供了两种导航方式：Tab 和 Drawer。当没有足够的空间来支持 tab 导航时，drawer 提供了另一个方便的选择。

In apps that use Material Design, there are two primary options for navigation: tabs and drawers. When there is insufficient space to support tabs, drawers provide a handy alternative.

在 Flutter中，我们可以将 Drawer widget 与 Scaffold 结合使用来创建一个具有 Material Design 风格的 Drawer 布局。请参见如下的步骤：

In Flutter, use the Drawer widget in combination with a Scaffold to create a layout with a Material Design drawer. This recipe uses the following steps:

步骤

Directions

创建一个 Scaffold
Create a Scaffold
添加一个 drawer
Add a drawer
向 drawer 中添加内容
Populate the drawer with items
通过编程关闭 drawer
Close the drawer programmatically

1. 创建一个 `Scaffold`

1. Create a `Scaffold`

为了向应用中添加一个 Drawer，我们需要将其放在 Scaffold widget 中。 Scaffold Widget 为遵循 Material 设计守则的应用程序提供了一套统一的可视化结构。它同样支持一些特殊的 Material Design 组件，例如 Drawer，AppBar 和 SnackBar 等。

To add a drawer to the app, wrap it in a Scaffold widget. The Scaffold widget provides a consistent visual structure to apps that follow the Material Design Guidelines. It also supports special Material Design components, such as Drawers, AppBars, and SnackBars.

在这个例子中，我们想要创建一个带有 drawer 的 Scaffold：

In this example, create a Scaffold with a drawer:

Scaffold(
  drawer: // Add a Drawer here in the next step.
);

2. 添加一个 drawer

2. Add a drawer

我们现在可以在 Scaffold 上添加一个 drawer。虽然 drawer 可以是任何 widget，但最好还是使用 Material Library 中的 Drawer widget，因为这样才符合 Material Design 设计规范。

Now add a drawer to the Scaffold. A drawer can be any widget, but it’s often best to use the Drawer widget from the material library, which adheres to the Material Design spec.

Scaffold(
  drawer: Drawer(
    child: // Populate the Drawer in the next step.
  )
);

3. 向 drawer 中添加内容

3. Populate the drawer with items

既然已经有了一个 Drawer，我们现在就可以向其中添加内容。在这个例子中，我们将使用 ListView。虽然你也可以使用 Column widget，但是 ListView 在这种情况下将是更好的选择，因为如果内容所占用的空间超出了屏幕的话，它将能够允许用户进行滚动。

Now that you have a Drawer in place, add content to it. For this example, use a ListView. While you could use a Column widget, ListView is handy because it allows users to scroll through the drawer if the content takes more space than the screen supports.

我们将使用 DrawerHeader 和两个 ListTile widget 填充 ListView。有关使用 List 的更多信息，请参阅实用教程中的 list recipes。

Populate the ListView with a DrawerHeader and two ListTile widgets. For more information on working with Lists, see the list recipes.

Drawer(
  // Add a ListView to the drawer. This ensures the user can scroll
  // through the options in the drawer if there isn't enough vertical
  // space to fit everything.
  child: ListView(
    // Important: Remove any padding from the ListView.
    padding: EdgeInsets.zero,
    children: <Widget>[
      DrawerHeader(
        child: Text('Drawer Header'),
        decoration: BoxDecoration(
          color: Colors.blue,
        ),
      ),
      ListTile(
        title: Text('Item 1'),
        onTap: () {
          // Update the state of the app.
          // ...
        },
      ),
      ListTile(
        title: Text('Item 2'),
        onTap: () {
          // Update the state of the app.
          // ...
        },
      ),
    ],
  ),
);

4. 通过编程关闭 drawer

4. Close the drawer programmatically

我们经常需要在用户点击某个项目后就将 Drawer 关掉。那么怎样才能做到这一点呢？请试试看 Navigator。

After a user taps an item, you might want to close the drawer. You can do this by using the Navigator.

当用户打开 Drawer 时，Flutter 会将 drawer widget 覆盖在当前的导航堆栈上。因此，要关闭 drawer，我们可以通过调用 Navigator.pop(context) 来实现。

When a user opens the drawer, Flutter adds the drawer to the navigation stack. Therefore, to close the drawer, call Navigator.pop(context).

ListTile(
  title: Text('Item 1'),
  onTap: () {
    // Update the state of the app.
    // ...
    // Then close the drawer.
    Navigator.pop(context);
  },
),

交互式样例

Interactive example

import 'package:flutter/material.dart';

void main() => runApp(MyApp());

class MyApp extends StatelessWidget {
  final appTitle = 'Drawer Demo';

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: appTitle,
      home: MyHomePage(title: appTitle),
    );
  }
}

class MyHomePage extends StatelessWidget {
  final String title;

  MyHomePage({Key key, this.title}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: Text(title)),
      body: Center(child: Text('My Page!')),
      drawer: Drawer(
        // Add a ListView to the drawer. This ensures the user can scroll
        // through the options in the drawer if there isn't enough vertical
        // space to fit everything.
        child: ListView(
          // Important: Remove any padding from the ListView.
          padding: EdgeInsets.zero,
          children: <Widget>[
            DrawerHeader(
              child: Text('Drawer Header'),
              decoration: BoxDecoration(
                color: Colors.blue,
              ),
            ),
            ListTile(
              title: Text('Item 1'),
              onTap: () {
                // Update the state of the app
                // ...
                // Then close the drawer
                Navigator.pop(context);
              },
            ),
            ListTile(
              title: Text('Item 2'),
              onTap: () {
                // Update the state of the app
                // ...
                // Then close the drawer
                Navigator.pop(context);
              },
            ),
          ],
        ),
      ),
    );
  }
}

步骤