为接受参数/实参的类创建一个单例工厂

Factory用于生成对象而不是管理对象。我认为DB连接管理器更适合您的情况。您可以将管理器声明为单例。对于单个连接，可以使用内部类/结构。

见下面的例子:

class DBConnectionManager
{        
    struct Connection
    {
      public string Hostname;
      public string ServerName;
      public string UserName;
      public string Password;
      public void Connect()
      {
      }
      public void Close()
      {
      } 
    }
    private static s_instance;
    public static DBConnectionManager Instance
    {
        get {return s_instance; }
    }
    private List<Connection> m_connections;
    public Connection GetConnection(string hostname, string serverName, string userName, string password)
    {
        // if already exist in m_connections
        // return the connection
        // otherwise create new connection and add to m_connections    
    }
    public void CloseConnection(string hostname, string serverName, string userName, string password)
    {
        // if find it in m_connections
        // then call Close()
    }
    public void CloseAll()
    {
        //
    }        
} 

所以我已经这样做了，它的工作…你能告诉我它是否正确吗?它也是线程安全的吗?

public Class A 
{
    private A(string hostname, string port, string username, string pw_hash) {
        //create a new instance with the specified parameters
    }
    //other methods on the connection
    protected void close() {
        //close the connection
    }
    public class AFactory 
    {
    private IList<A> connections = new List<A>();
    private AFactory()
    {
        //do something
    }
    private static readonly Lazy<AFactory> lazy
        = new Lazy<AFactory>(() => new AFactory());
    public static AFactory Instance { get { return lazy.Value; } }
    public A getA(string hostname, string service, string username, string pw_hash)
    {
        foreach (A a in connections)
        {
            if (a.hostname == hostname && a.service == service && a.username == username)
                return a;
        }
        A d = new A(hostname, service, username, pw_hash);
        connections.Add(d);
        return d;
    }
    }
}

我是这样使用它的:

A.AFactory fact = A.AFactory.Instance;
A conn = fact.getA(a, b, c, d);
A conn2 = fact.getA(e, f, g, h);

这个实现是否有明显的错误?

你可以试试:

public static class Singlett<Param,T>
   where T : class
{
    static volatile Lazy<Func<Param, T>> _instance;
    static object _lock = new object();
    static Singlett()
    {
    }
    public static Func<Param, T> Instance
    {
        get
        {
            if (_instance == null)
            {
                _instance = new Lazy<Func<Param, T>>(() =>
                {
                    lock (Singlett<Param,T>._lock)
                    {
                        try
                        {
                            ConstructorInfo constructor = null;
                            Type[] methodArgs = { typeof(Param) };                                
                            constructor = typeof(T).GetConstructor(BindingFlags.Instance | BindingFlags.NonPublic, null, methodArgs, null);// Binding flags excludes public constructors.
                            if (constructor == null)
                            {
                                constructor = typeof(T).GetConstructor(BindingFlags.Public, null, methodArgs, null);
                                if (constructor == null)
                                    return delegate(Param o) { return (T)Activator.CreateInstance(typeof(T), new object[] { o }); };
                            }
                            return delegate(Param o) { return (T)constructor.Invoke(new object[] { o }); };
                        }
                        catch (Exception exception)
                        {
                            throw exception;
                        }
                    }
                });
            }
            return _instance.Value;
        }
    }
}

然后使用它:而不是

int i = 10;
MyClass class = new MyClass(i);

你可以写:

int i = 10;
MyClass class = Singlett<int,MyClass>.Instance(i);

试试这个:

该接口从工厂初始化器中公开，并包含公开的方法和属性。

public interface IDatabase
{
    string ConnectionString { get; set; }
    IDataReader ExecuteSql(string sql);
}

工厂基抽象类，其中可以对不同类型的数据库工厂执行通用功能。

public abstract class FactoryBase
{
    public FactoryBase() { }
    public abstract IDatabase GetDataLayer();
}

包含调用的具体sql类。看一下ExecuteSql方法。该连接在命令中是自包含的，因此您不必担心打开、关闭和处理它。

public class SQL : IDatabase
{
    private string m_ConnectionString = string.Empty;
    public string ConnectionString
    {
        get { return m_ConnectionString; }
        set { m_ConnectionString = value; }
    }
    public IDataReader ExecuteSql(string sql)
    {
        using (var command = new SqlCommand(sql, new SqlConnection(ConnectionString)) { CommandType = CommandType.Text, CommandText = sql, CommandTimeout = 0 })
        {
            if (command.Connection.State != ConnectionState.Open) command.Connection.Open();
            return command.ExecuteReader();
        }
    }
}

创建Sql具体类实例的Sql工厂类。

class SQLFactory : FactoryBase
{
    public override IDatabase GetDataLayer()
    {
        return new SQL();
    }
}

工厂初始化器类，开发人员将使用它来传递工厂类型，并返回iddatabase。

public static class FactoryInitializer
{
    public static IDatabase LoadFactory<T>(string connectionstring) where T : FactoryBase, new()
    {
        var factory = new T();
        var data = factory.GetDataLayer();
        data.ConnectionString = connectionstring;
        return data;
    }
}

:

var factory = FactoryInitializer.LoadFactory<SQLFactory>(connectionString);
factory.ExecuteSql("SELECT ...");

您可以创建一个OracleFactory和一个Oracle具体类，并以相同的方式使用它们。