Use case

• If --dart-define has many definitions, the startup command can be very long and error-prone
• It is especially difficult to maintain if there are multiple packages to switch
• Also I want these definitions to be available directly in android and iOS

We counted, our project package includes countries: Brazil, Singapore, Europe, we have a total of 36 configuration items in each region

In my app, different regions and languages use different package names for internationalization. Different package names google-ad, google-service.json, facebook, and firebase have different configurations. It is very cumbersome to switch between definitions. Centralized management and configuration are required to avoid business trips

So I hope ：

• Use project variables directly in android build.gradle
• Use environment variables directly in iOS

Proposal

I have a PR ，hope you can give some advice, thanks ! (Because I was not familiar with the process in the early stage, I raised PR first, sorry again)

Add a new flag to support config constants pool by json file

1、Define json file

flutter build apk  --define-config-json-file=cn.com.test.pkg.json

You can use flutter run --help get usage

    --dart-define=<foo=bar>                       Additional key-value pairs that will be available as constants from the String.fromEnvironment, bool.fromEnvironment, int.fromEnvironment, and double.fromEnvironment constructors.
                                                  Multiple defines can be passed by repeating "--dart-define" multiple times.
    --define-config-json-file                     The path of a json format file where flutter define a global constant pool. Use `const String.fromEnvironment("DEFINE_CONFIG_JSON_RAW_VALUE")` can get all config json file raw
                                                  value. Json entry will be available as constants from the String.fromEnvironment, bool.fromEnvironment, int.fromEnvironment, and double.fromEnvironment constructors;the key is json
                                                  filed key,get value is json value.

for example: cn.com.test.pkg.json content

{
  "facebookAppId": "xxx",
  "versionName": "1.0.0",
  "label": "xxx xxx",
  "versionCode": 1,
  "android_applicationId": "com.xxx.br",
  "googleAndroidApiKey": "xxxx",
  "googleAndroidAppId": "1:xxx:android:xxx",
  "googleAndroidMessagingSenderId": "xxx",
  "schemeHost": "first.xxx.com",
  "scheme": "xxxxx",
  "privacyProtocol": "https://xxxx.com/privacyProtocol.html",
  "teamsOfService": "https://xxx.com/teamsOfService.html",
  "androidChannel": "1OSH1PP64X",
  "iosChannel": "1J6C22IH91",
  "iosUploadCSymS": "false",
  "universalLinkDomain": "br.xxx.com"
}

2、Use environment in flutter

You can get all json raw content:

var configRaw =
        const String.fromEnvironment("DEFINE_CONFIG_JSON_RAW_VALUE", defaultValue: "{}");
var  configRaw = utf8.decode(base64Decode(configRaw));

Or ,you can get field by

var facebookAppId =
        const String.fromEnvironment("facebookAppId", defaultValue: "");

3、Android project

file: build.gradle

// This then uses the project variable
    buildTypes {
        release {
            manifestPlaceholders = [
                    faceBook_appId       : facebookAppId
            ]

            resValue "string", "facebook_app_id", facebookAppId

…………
// switch profile
task switchToGoogleServices(type: Copy) {
    description = "Switches google-services config,from google-services.${android_applicationId}.json to google-services.json"
    println(description)
    from "../../precompileConfigs/google-services"
    include "google-services.${android_applicationId}.json"
    into "./"
    rename "google-services.${android_applicationId}.json", 'google-services.json'
}

4、iOS project

file: ios/Flutter/Generated.xcconfig

  facebookAppId=xxx
  versionCode=1
  android_applicationId=com.xxx.br
  ios_bundle_identifier=com.xxx.xxxx.nomodify
 ……

file: ios/Flutter/flutter_export_environment.sh

export "facebookAppId=xxx"
export "versionCode=1"
export "android_applicationId=com.xxx.br"
export "ios_bundle_identifier=com.xxx.xxxx.nomodify"
……

You can use in Info.plist

	<key>CFBundleIdentifier</key>
	<string>$(ios_bundle_identifier)</string>