單例寫法

class Singleton{

  Singleton._privateConstructor();

  static final Singleton _instance = Singleton._privateConstructor();

  static Singleton get instance { return _instance;}

}

Dio單例

class DioManager {
  //寫一個(gè)單例
  DioManager._privateConstructor();
  static Dio _dio = new Dio();
  static DioManager? _instance;

  static DioManager? getInstance() {
    if (_instance == null) {
      _instance = DioManager._privateConstructor();
    }
    _instance!._init();
    return _instance;
  }

  _init() {
    _dio.options.baseUrl = Constant.baseUrl;
    _dio.options.connectTimeout = 5000;
    _dio.options.receiveTimeout = 3000;
    _dio.interceptors.add(LogInterceptor(responseBody: true)); //是否開啟請(qǐng)求日志
  }
}

測試是否每次都得到一樣的實(shí)例

var s = identical(a, b);
print("選中s index = $s");