Flutter開發環境搭建和調試

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Flutter開發工具很多，有很多支持Flutter開發的IDE。比如Android Studio、Visual Studio Code、InteIIiJ IDEA、Atom、Komodo等。這裏將使用Visual Studio Code作爲主要開發工具，因爲Visual Studio Code佔用內存和CPU比較低，非常的流暢，體驗也比較的好。模擬器的話，這裏推薦使用Android官方的模擬器，也就是Android Studio SDK裏帶的模擬器。不過，這裏的模擬器我們使用單獨啓動的，無需從Android Studio啓動，當然也可以用真機運行調試。接下來，我們就開始Flutter開發環境的搭建吧。注意：本文是在Windows環境下安裝的開發環境。本文將主要介紹：

• Flutter下載與環境變量配置
• Visual Studio Code插件安裝與新建Flutter項目
• 模擬器的安裝
• 運行Flutter項目到模擬器和真機
• Flutter常用命令

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開發環境的搭建

1. 下載Flutter SDK

Flutter SDK由兩部分構成，一個是Dart SDK，另一個就是Flutter SDK，因爲Flutter是基於Dart的。可以通過兩種方式下載：一種是Git下載；另一種是直接下載SDK壓縮包即可。
Git方式我們可以通過拉取官方Github上的flutter分支來下載。分支分類如下圖：

可以看到主要有dev、beta和stable三個官方分支使，這裏正式開發的話可以下載stable穩定版本。用Git命令進行下載stable分支：

git clone -b stable https://github.com/flutter/flutter.git

另一種是直接官網下載SDK壓縮包，官方下載地址爲：

https://storage.googleapis.com/flutter_infra/releases/stable/windows/flutter_windows_v1.0.0-stable.zip

2. 配置環境變量

下載完SDK後我們可以把它解壓放到指定文件夾裏，接下來就是配置SDK環境變量量，這樣我們就可以在需要的目錄執行相關命令了。如果在官網更新下載SDK慢的話，可以設置國內的鏡像代理地址，這樣下載會快一些。可以將如下的國內下載鏡像地址加入到環境變量中：

變量名：PUB_HOSTED_URL，變量值：https://pub.flutter-io.cn
變量名：FLUTTER_STORAGE_BASE_URL，變量值：https://storage.flutter-io.cn

Flutter SDK環境變量，講flutter的bin目錄加入環境變量即可：

[你的Flutter文件夾路徑]\flutter\bin

這樣我們的Flutter SDK的環境變量就配置完畢了。接下來在命令提示符窗口中輸入命令：

flutter doctor

它可以幫助我們檢查Flutter環境變量是否設置成功，Android SDK是否下載以及配置好環境變量等等。如果有相關的錯誤提示，根據提示進行修復和安裝、設置即可。每次運行這個命令，都會幫你檢查是否缺失了必要的依賴。通過運行flutter doctor命令來驗證你是否已經正確地設置了，並且可以自動更新和下載相關的依賴。如果全部配置正確的話，會出現如下類似的檢測信息：

主要檢測信息爲：Flutter、Android toolchain、Connected device。

3．安裝Visual Studio Code所需插件

在Visual Studio Code的Extensions裏搜索安裝Dart和Flutter擴展插件：

安裝完成插件後，重啓Visual Studio Code編輯器即可。

4．創建Flutter項目

接下來進行Flutter項目的新建，我們可以通過命令面板或者快捷鍵Ctrl+Shif+P打開命令面板，找到Flutter：New Project：

點擊New Project，接下來進入項目名稱輸入：

回車，然後選擇好項目的存儲位置即可，這樣就完成了Flutter項目的新建。
整個的創建流程日誌如下：

[undefined] flutter create .
Waiting for another flutter command to release the startup lock...
Creating project ....
  .gitignore (created)
  .idea\libraries\Dart_SDK.xml (created)
  .idea\libraries\Flutter_for_Android.xml (created)
  .idea\libraries\KotlinJavaRuntime.xml (created)
  .idea\modules.xml (created)
  .idea\runConfigurations\main_dart.xml (created)
  .idea\workspace.xml (created)
  .metadata (created)
  android\app\build.gradle (created)
  android\app\src\main\java\com\example\fluttersamples\MainActivity.java (created)
  android\build.gradle (created)
  android\flutter_samples_android.iml (created)
  android\app\src\main\AndroidManifest.xml (created)
  android\app\src\main\res\drawable\launch_background.xml (created)
  android\app\src\main\res\mipmap-hdpi\ic_launcher.png (created)
  android\app\src\main\res\mipmap-mdpi\ic_launcher.png (created)
  android\app\src\main\res\mipmap-xhdpi\ic_launcher.png (created)
  android\app\src\main\res\mipmap-xxhdpi\ic_launcher.png (created)
  android\app\src\main\res\mipmap-xxxhdpi\ic_launcher.png (created)
  android\app\src\main\res\values\styles.xml (created)
  android\gradle\wrapper\gradle-wrapper.properties (created)
  android\gradle.properties (created)
  android\settings.gradle (created)
  ios\Runner\AppDelegate.h (created)
  ios\Runner\AppDelegate.m (created)
  ios\Runner\main.m (created)
  ios\Runner.xcodeproj\project.pbxproj (created)
  ios\Runner.xcodeproj\xcshareddata\xcschemes\Runner.xcscheme (created)
  ios\Flutter\AppFrameworkInfo.plist (created)
  ios\Flutter\Debug.xcconfig (created)
  ios\Flutter\Release.xcconfig (created)
  ios\Runner\Assets.xcassets\AppIcon.appiconset\Contents.json (created)
  ios\Runner\Assets.xcassets\AppIcon.appiconset\[e-mail] (created)
  ios\Runner\Assets.xcassets\AppIcon.appiconset\[e-mail] (created)
  ios\Runner\Assets.xcassets\AppIcon.appiconset\[e-mail] (created)
  ios\Runner\Assets.xcassets\AppIcon.appiconset\[e-mail] (created)
  ios\Runner\Assets.xcassets\AppIcon.appiconset\[e-mail] (created)
  ios\Runner\Assets.xcassets\AppIcon.appiconset\[e-mail] (created)
  ios\Runner\Assets.xcassets\AppIcon.appiconset\[e-mail] (created)
  ios\Runner\Assets.xcassets\AppIcon.appiconset\[e-mail] (created)
  ios\Runner\Assets.xcassets\AppIcon.appiconset\[e-mail] (created)
  ios\Runner\Assets.xcassets\AppIcon.appiconset\[e-mail] (created)
  ios\Runner\Assets.xcassets\AppIcon.appiconset\[e-mail] (created)
  ios\Runner\Assets.xcassets\AppIcon.appiconset\[e-mail] (created)
  ios\Runner\Assets.xcassets\AppIcon.appiconset\[e-mail] (created)
  ios\Runner\Assets.xcassets\AppIcon.appiconset\[e-mail] (created)
  ios\Runner\Assets.xcassets\AppIcon.appiconset\[e-mail] (created)
  ios\Runner\Assets.xcassets\LaunchImage.imageset\Contents.json (created)
  ios\Runner\Assets.xcassets\LaunchImage.imageset\LaunchImage.png (created)
  ios\Runner\Assets.xcassets\LaunchImage.imageset\[e-mail] (created)
  ios\Runner\Assets.xcassets\LaunchImage.imageset\[e-mail] (created)
  ios\Runner\Assets.xcassets\LaunchImage.imageset\README.md (created)
  ios\Runner\Base.lproj\LaunchScreen.storyboard (created)
  ios\Runner\Base.lproj\Main.storyboard (created)
  ios\Runner\Info.plist (created)
  ios\Runner.xcodeproj\project.xcworkspace\contents.xcworkspacedata (created)
  ios\Runner.xcworkspace\contents.xcworkspacedata (created)
  lib\main.dart (created)
  flutter_samples.iml (created)
  pubspec.yaml (created)
  README.md (created)
  test\widget_test.dart (created)
Running "flutter packages get" in flutter_samples...            11.8s
Wrote 64 files.

All done!
[√] Flutter is fully installed. (Channel stable, v1.0.0, on Microsoft Windows [Version 10.0.17134.590], locale zh-CN)
[√] Android toolchain - develop for Android devices is fully installed. (Android SDK 28.0.3)
[√] Android Studio is fully installed. (version 3.3)
[√] IntelliJ IDEA Community Edition is fully installed. (version 2018.3)
[!] Connected device is not available.

Run "flutter doctor" for information about installing additional components.

In order to run your application, type:

  $ cd .
  $ flutter run

Your application code is in .\lib\main.dart.

exit code 0

Flutter項目結構如下：

其中，Android相關的修改和配置在android目錄下，結構和Android應用項目結構一樣；IOS相關修改和配置在ios目錄下，結構和IOS應用項目結構一樣。最重要的flutter代碼文件是在lib目錄下，類文件以.dart結尾，語法結構爲Dart語法結構。大致如下：

import 'package:flutter/material.dart';

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

class MyApp extends StatelessWidget {
  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        // This is the theme of your application.
        //
        // Try running your application with "flutter run". You'll see the
        // application has a blue toolbar. Then, without quitting the app, try
        // changing the primarySwatch below to Colors.green and then invoke
        // "hot reload" (press "r" in the console where you ran "flutter run",
        // or simply save your changes to "hot reload" in a Flutter IDE).
        // Notice that the counter didn't reset back to zero; the application
        // is not restarted.
        primarySwatch: Colors.blue,
      ),
      home: MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

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

  // This widget is the home page of your application. It is stateful, meaning
  // that it has a State object (defined below) that contains fields that affect
  // how it looks.

  // This class is the configuration for the state. It holds the values (in this
  // case the title) provided by the parent (in this case the App widget) and
  // used by the build method of the State. Fields in a Widget subclass are
  // always marked "final".

  final String title;

  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  int _counter = 0;

  void _incrementCounter() {
    setState(() {
      // This call to setState tells the Flutter framework that something has
      // changed in this State, which causes it to rerun the build method below
      // so that the display can reflect the updated values. If we changed
      // _counter without calling setState(), then the build method would not be
      // called again, and so nothing would appear to happen.
      _counter++;
    });
  }

  @override
  Widget build(BuildContext context) {
    // This method is rerun every time setState is called, for instance as done
    // by the _incrementCounter method above.
    //
    // The Flutter framework has been optimized to make rerunning build methods
    // fast, so that you can just rebuild anything that needs updating rather
    // than having to individually change instances of widgets.
    return Scaffold(
      appBar: AppBar(
        // Here we take the value from the MyHomePage object that was created by
        // the App.build method, and use it to set our appbar title.
        title: Text(widget.title),
      ),
      body: Center(
        // Center is a layout widget. It takes a single child and positions it
        // in the middle of the parent.
        child: Column(
          // Column is also layout widget. It takes a list of children and
          // arranges them vertically. By default, it sizes itself to fit its
          // children horizontally, and tries to be as tall as its parent.
          //
          // Invoke "debug painting" (press "p" in the console, choose the
          // "Toggle Debug Paint" action from the Flutter Inspector in Android
          // Studio, or the "Toggle Debug Paint" command in Visual Studio Code)
          // to see the wireframe for each widget.
          //
          // Column has various properties to control how it sizes itself and
          // how it positions its children. Here we use mainAxisAlignment to
          // center the children vertically; the main axis here is the vertical
          // axis because Columns are vertical (the cross axis would be
          // horizontal).
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            Text(
              'You have pushed the button this many times:',
            ),
            Text(
              '$_counter',
              style: Theme.of(context).textTheme.display1,
            ),
          ],
        ),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: _incrementCounter,
        tooltip: 'Increment',
        child: Icon(Icons.add),
      ), // This trailing comma makes auto-formatting nicer for build methods.
    );
  }
}

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模擬器的安裝與調試

項目新建完畢了，接下來就是編譯運行Flutter項目到真機或者模擬器了。先說模擬器，模擬器在我們下載的Android SDK的目錄裏，可以通過兩種方法創建模擬器，推薦在Android Studio裏新建一個模擬器，點擊進入AVD Manager，如果沒有模擬器的話，就創建一個即可，可以選擇最新的SDK：

創建完畢後，我們就可以在電腦的模擬器目錄看到我們創建的模擬器裏：

對應的模擬器AVD Manager相關也在Android SDK目錄下：

接下來我們就可以關閉相關窗口了，建立一個bat文件，寫入啓動模擬器的命令，這樣每次啓動模擬器直接運行這個bat文件即可：

D:\Sdk\emulator\emulator.exe -avd Pixel_XL_API_28

模擬器所在的SDK目錄根據你的實際情況位置修改即可。

接下來，雙擊這個bat文件運行模擬器：

接着在項目所在目錄運行flutter run命令即可編譯運行flutter項目到模擬器上：

運行效果如下圖：

運行成功後，後續運行調試只要不退出應用界面，就可以進行熱重載，輸入r進行熱重載當前頁面，輸入R進行整個應用的熱重啓，輸入h彈出幫助信息，輸入d解除關聯，輸入q退出應用調試。如果遇到有多個模擬器或者模擬器和真機同時存在的話，可以通過-d參數加設備ID指定要運行的設備，例如：

flutter run -d emulator-5556

可以通過flutter devices或adb devices命令查看目前已連接的設備信息。
還有一種命令方式創建模擬器，輸入如下命令可以查看當前可用的模擬器：

flutter emulator

輸入以下命令可以創建指定名稱的模擬器，默認創建的模擬器Android版本號爲已安裝的最新的SDK版本號：

flutter emulators --create --name xyz

運行以下命令可以啓動模擬器：

flutter emulators --launch <emulator id>

替換爲你的模擬器ID名稱即可。
真機設備運行調試和模擬器的過程基本一樣，手機和電腦通過USB連接，手機開啓開發人員選項和USB調試，最後運行flutter run命令即可。
其他常用的命令如下：

flutter build apk;           //打包Android應用
flutter build apk –release;
flutter install;              //安裝應用
flutter build ios;            //打包IOS應用
flutter build ios –release;
flutter clean;               //清理重新編譯項目
flutter upgrade;            //升級Flutter SDK和依賴包
flutter channel;            //查看Flutter官方分支列表和當前項目使用的Flutter分支
flutter channel <分支名>;   //切換分支

好了，Flutter開發環境搭建和調試就爲大家講解到這裏了。