C# 反射 - 根据可用参数选择构造函数重载

Question

我编写了一个通用数据库类，可以调用它来执行通用数据库 (CRUD) 操作，从而避免在多个解决方案中重写 ADO.NET 代码。为了使其灵活，根据不同的数据库身份验证类型和实例类型等，有许多构造函数重载。类如下:

class Database
{
    // default instance with Windows authentication
    // constructor 1
    public Database(string server, string database, bool persistSecurityInfo)
    {
        _server = server;
        _database = database;
        _persistSecurityInfo = persistSecurityInfo;
        _integratedSecurity = "True";
        _connectionString = "Data Source=" + server + ";Initial Catalog=" + database + ";Persist Security Info=" + persistSecurityInfo.ToString() + ";Integrated Security=True";
    }

    // named instance using Windows authentication
    // constructor 2
    public Database(string server, string instance, string database, bool persistSecurityInfo) : this(server, database, persistSecurityInfo)
    {
        _instance = instance;
        _integratedSecurity = "True";
        _connectionString = "Data Source=" + server + "\\" + instance + ";Initial Catalog=" + database + ";Persist Security Info=" + persistSecurityInfo.ToString() + ";Integrated Security=True";
    }

    // default instance with SQL authentication
    // constructor 3
    public Database(string server, string database, bool persistSecurityInfo, string userName, string password) : this(server, database, persistSecurityInfo)
    {
        _userName = userName;
        _password = password;
        _integratedSecurity = "False";
        _connectionString = "Data Source=" + server + ";Initial Catalog=" + database + ";Persist Security Info=" + persistSecurityInfo.ToString() + ";User ID=" + userName + ";Password=" + password;
    }

    // named instance with SQL authentication
    // constructor 4
    public Database(string server, string instance, string database, bool persistSecurityInfo, string userName, string password) : this(server, database, persistSecurityInfo, userName, password)
    {
        _instance = instance;
        _integratedSecurity = "False";
        _connectionString = "Data Source=" + server + "\\" + instance + ";Initial Catalog=" + database + ";Persist Security Info=" + persistSecurityInfo.ToString() + ";User ID=" + userName + ";Password=" + password;
    }

    private string _server;
    private string _instance;
    private string _database;
    private bool _persistSecurityInfo;
    private string _userName;
    private string _password;
    private string _integratedSecurity;

    private string _connectionString;
    private string _query;

    //CRUD Methods here
}

我编写了一个正在写入数据库的控制台应用程序。当应用程序执行时，用户提供一些命令行开关。

部分开关如下(还有其他与程序运行有关的开关，我没有在这里包括):

• /s : 数据库服务器名称
• /i : 数据库实例名
• /d : 数据库名
• /n:集成安全性(对或错)
• /u : 数据库用户名
• /p : 数据库密码

/i、/u 和/p 是可选的(例如，如果未提供实例名称，程序假定它连接到/s 上的默认实例)

因此，我需要程序在运行时根据提供的参数决定调用哪个构造函数。

这里是伪例子

Class Program
{
    static void Main(string[] args)
    {
         foreach (string arg in args[])
         {
             //code to work out which parameters have been provided here and adds them to array. Also other code which checks integrity such as ensuring there is no username without a password and vice versa etc.
             string[] suppliedParameters;

             //if there is a /i , /u , /p parameters, use constructor 4
             //if there is a /u and /p but no /i, use constructor 3
             //if there is an /i but no /u or /n use constructor 2
             //if there is no /i, /u or /n, use constructor 1
         }
    }
}

我知道我可以使用反射来执行相关的构造函数，并且我可以在 Main 方法中使用 switch 语句来实现对构造函数的选择，该方法在上面的逻辑中执行测试，但我只是想知道是否有可能更优雅的方式来做到这一点？

Answer 1

如果您想使用反射，请使用Activator.CreateInstance 方法，该方法接受对象的类型和数组作为参数。它会根据数组中的项数和项类型自动调用所需的构造函数。

object[] arguments = //Create array based on input
DataBase db=(DataBase)Activator.CreateInstance(typeof(Database), arguments); // This will call matching constructor based on array passed