Abstract Factory Pattern 抽象工厂模式简介与 C# 示例【创建型】【设计模式来了】

〇、简介

1、什么是抽象工厂模式？

一句话解释：

  通过对抽象类和抽象工厂的一组实现，独立出一系列新的操作，客户端无需了解其逻辑直接访问。

抽象工厂模式（Abstract Factory Pattern）是一种创建型模式。它用于创建一组相关对象的家族。强调的是一组对象之间的协作关系，而不是单个对象之间的依赖关系。抽象工厂类负责创建整个家族的对象的生命周期，并隐藏与实现有关的逻辑。

 一个比喻：（科目与课代表）

  语文和数学的课代表和副课代表，都按照抽象方法标准选好了，接下来同样的通过实现抽象类和接口标准，来选出两名物理课代表。当然，已经选出来的其他课代表，和本次选举无关联。

2、优缺点和使用场景

优点：

• 可以降低系统中各个对象之间的耦合度。
• 隔离了具体类的生产，使得客户并不需要知道什么被创建。
• 增加新的具体工厂和产品族很方便，无须修改已有系统，符合“开闭原则”。

缺点：

• 在增加新的产品方面比较困难，需要修改抽象工厂的接口，这样会导致所有的具体工厂也需要做出相应的修改。
• 抽象程度高，可能会导致一些底层实现细节难以控制。

总之，抽象工厂模式能够有效地封装对象创建，但是扩展产品较为困难。它在软件开发中被广泛使用，特别是在跨平台软件开发中经常用到，使用时要注意系统对象的特点合理使用。

 使用场景举例：

• 游戏开发：游戏中可能需要多种角色、武器、敌人等元素，它们之间可能存在关联性或依赖性，可以使用抽象工厂方法来快速构建游戏元素。
• 数据库访问组件设计：不同数据库的连接、查询和数据存储方式可能存在差异，可以使用抽象工厂方法来创建不同数据库的访问组件、驱动和映射器。
• 操作系统界面设计：不同操作系统的界面设计具有不同的特点，可以使用抽象工厂方法来创建不同操作系统下的控件。

总之，使用抽象工厂模式，都需要保证对象家族之间高内聚、松耦合，使得系统的设计和实现更加灵活和可扩展。

一、抽象工厂模式简单实现与扩展

通过两个抽象产品类 ProductA/ProductBBBB，实现四个具体产品类；在通过抽象工厂接口 IAbstractFactory，实现两个具体工厂的产品族 ConcreteFactory1/ConcreteFactory2。最后通过 Client 类注入工厂类的同时，创建产品的不同产品的实例，使客户端不用了解产品如何实例化，可以直接引用。

// 抽象产品类。
public abstract class ProductA
{
    public abstract void OperationA();
}
public abstract class ProductBBBB
{
    public abstract void OperationBBBB();
}

// 具体产品类，其中 ProductA1、ProductA2、ProductB1 和 ProductB2 分别代表不同的产品。
public class ProductA1 : ProductA
{
    public override void OperationA()
    {
        Console.WriteLine("ProductA1's operation.");
    }
}
public class ProductA2 : ProductA
{
    public override void OperationA()
    {
        Console.WriteLine("ProductA2's operation.");
    }
}
public class ProductBBBB1 : ProductBBBB
{
    public override void OperationBBBB()
    {
        Console.WriteLine("ProductBBBB1's operation.");
    }
}
public class ProductBBBB2 : ProductBBBB
{
    public override void OperationBBBB()
    {
        Console.WriteLine("ProductBBBB2's operation.");
    }
}

// 抽象工厂接口，定义了各种不同产品族的生产方法。
public interface IAbstractFactory
{
    ProductA CreateProductA();
    ProductBBBB CreateProductBBBB();
}
// 每个具体工厂都能够生产特定的产品族。
public class ConcreteFactory1 : IAbstractFactory
{
    public ProductA CreateProductA()
    {
        return new ProductA1();
    }
    public ProductBBBB CreateProductBBBB()
    {
        return new ProductBBBB1();
    }
}
public class ConcreteFactory2 : IAbstractFactory
{
    public ProductA CreateProductA()
    {
        return new ProductA2();
    }
    public ProductBBBB CreateProductBBBB()
    {
        return new ProductBBBB2();
    }
}

// 客户端代码使用抽象工厂来创建各种不同产品族的产品，而无需关心它们的实际实现。
public class Client
{
    private readonly ProductA _productA;
    private readonly ProductBBBB _productBBBB;
    public Client(IAbstractFactory factory)
    {
        _productA = factory.CreateProductA();
        _productBBBB = factory.CreateProductBBBB();
    }
    public void Run()
    {
        _productA.OperationA();
        _productBBBB.OperationBBBB();
    }
}

// 测试
static void Main(string[] args)
{
    Client client = new Client(new ConcreteFactory1());
    client.Run();
    Client client2 = new Client(new ConcreteFactory2());
    client2.Run();

    // 输出：
    // ProductA1's operation.
    // ProductBBBB1's operation.
    // ProductA2's operation.
    // ProductBBBB2's operation.
}

下面我们尝试扩展出来一个新的产品 3：

// 具体产品类
public class ProductA3 : ProductA
{
    public override void OperationA()
    {
        Console.WriteLine("ProductA3's operation.");
    }
}
public class ProductBBBB3 : ProductBBBB
{
    public override void OperationBBBB()
    {
        Console.WriteLine("ProductBBBB3's operation.");
    }
}
// 具体工厂都能够生产特定的产品族
public class ConcreteFactory3 : IAbstractFactory
{
    public ProductA CreateProductA()
    {
        return new ProductA3();
    }
    public ProductBBBB CreateProductBBBB()
    {
        return new ProductBBBB3();
    }
}

测试：

static void Main(string[] args)
{
    Client client = new Client(new ConcreteFactory1());
    client.Run();
    Client client2 = new Client(new ConcreteFactory2());
    client2.Run();
    Client client3 = new Client(new ConcreteFactory3());
    client3.Run();
}

  

二、抽象工厂模式在 .net 框架中的实际应用

例如 DbProviderFactory，这个类位于 System.Data.Common.dll 程序集中，该类扮演抽象工厂模式中抽象工厂的角色，源码如下：

// System.Data.Common, Version=5.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a
// System.Data.Common.DbProviderFactory
using System.Data.Common;
public abstract class DbProviderFactory
{
	private bool? _canCreateDataAdapter;
	private bool? _canCreateCommandBuilder;
	public virtual bool CanCreateDataSourceEnumerator => false;
	public virtual bool CanCreateDataAdapter
	{
		get
		{
			if (!_canCreateDataAdapter.HasValue)
			{
				using DbDataAdapter dbDataAdapter = CreateDataAdapter();
				_canCreateDataAdapter = dbDataAdapter != null;
			}
			return _canCreateDataAdapter.Value;
		}
	}
	public virtual bool CanCreateCommandBuilder
	{
		get
		{
			if (!_canCreateCommandBuilder.HasValue)
			{
				using DbCommandBuilder dbCommandBuilder = CreateCommandBuilder();
				_canCreateCommandBuilder = dbCommandBuilder != null;
			}
			return _canCreateCommandBuilder.Value;
		}
	}
	public virtual DbCommand? CreateCommand()
	{
		return null;
	}
	public virtual DbCommandBuilder? CreateCommandBuilder()
	{
		return null;
	}
	public virtual DbConnection? CreateConnection()
	{
		return null;
	}
	public virtual DbConnectionStringBuilder? CreateConnectionStringBuilder()
	{
		return null;
	}
	public virtual DbDataAdapter? CreateDataAdapter()
	{
		return null;
	}
	public virtual DbParameter? CreateParameter()
	{
		return null;
	}
	public virtual DbDataSourceEnumerator? CreateDataSourceEnumerator()
	{
		return null;
	}
}

下面是 SqlClientFactory.cs，继承了抽象类 DbProviderFactory，需要注意的是，此为引用程序集，即只包含元数据，不含可执行代码。如何通过工厂模式访问 SQLServer 数据库，可以参考官网示例： 获取 DbProviderFactory

点击查看 SqlClientFactory.cs

 // System.Data.SqlClient, Version=4.6.1.1, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a
// System.Data.SqlClient.SqlClientFactory
using System.Data.Common;
using System.Data.SqlClient;

/// <summary>Represents a set of methods for creating instances of the <see cref="N:System.Data.SqlClient" /> provider's implementation of the data source classes.</summary>
public sealed class SqlClientFactory : DbProviderFactory
{
	/// <summary>Gets an instance of the <see cref="T:System.Data.SqlClient.SqlClientFactory" />. This can be used to retrieve strongly typed data objects.</summary>
	public static readonly SqlClientFactory Instance;

	internal SqlClientFactory()
	{
	}

	/// <summary>Returns a strongly typed <see cref="T:System.Data.Common.DbCommand" /> instance.</summary>
	/// <returns>A new strongly typed instance of <see cref="T:System.Data.Common.DbCommand" />.</returns>
	public override DbCommand CreateCommand()
	{
		throw null;
	}

	/// <summary>Returns a strongly typed <see cref="T:System.Data.Common.DbCommandBuilder" /> instance.</summary>
	/// <returns>A new strongly typed instance of <see cref="T:System.Data.Common.DbCommandBuilder" />.</returns>
	public override DbCommandBuilder CreateCommandBuilder()
	{
		throw null;
	}

	/// <summary>Returns a strongly typed <see cref="T:System.Data.Common.DbConnection" /> instance.</summary>
	/// <returns>A new strongly typed instance of <see cref="T:System.Data.Common.DbConnection" />.</returns>
	public override DbConnection CreateConnection()
	{
		throw null;
	}

	/// <summary>Returns a strongly typed <see cref="T:System.Data.Common.DbConnectionStringBuilder" /> instance.</summary>
	/// <returns>A new strongly typed instance of <see cref="T:System.Data.Common.DbConnectionStringBuilder" />.</returns>
	public override DbConnectionStringBuilder CreateConnectionStringBuilder()
	{
		throw null;
	}

	/// <summary>Returns a strongly typed <see cref="T:System.Data.Common.DbDataAdapter" /> instance.</summary>
	/// <returns>A new strongly typed instance of <see cref="T:System.Data.Common.DbDataAdapter" />.</returns>
	public override DbDataAdapter CreateDataAdapter()
	{
		throw null;
	}

	/// <summary>Returns a strongly typed <see cref="T:System.Data.Common.DbParameter" /> instance.</summary>
	/// <returns>A new strongly typed instance of <see cref="T:System.Data.Common.DbParameter" />.</returns>
	public override DbParameter CreateParameter()
	{
		throw null;
	}
}

下面再看一下 Oracle 工厂的实现，完全独立于其他数据库的工厂：

点击查看源码 OracleClientFactory.cs

#region 程序集 Oracle.ManagedDataAccess, Version=4.122.21.1, Culture=neutral, PublicKeyToken=89b483f429c47342
// C:\Users\zheng\.nuget\packages\oracle.manageddataaccess\21.10.0\lib\net462\Oracle.ManagedDataAccess.dll
// Decompiled with ICSharpCode.Decompiler 7.1.0.6543
#endregion

using System;
using System.Data.Common;
using System.Security;
using System.Security.Permissions;
using OracleInternal.Common;

namespace Oracle.ManagedDataAccess.Client
{
    public sealed class OracleClientFactory : DbProviderFactory
    {
        public static readonly OracleClientFactory Instance = new OracleClientFactory();

        public override bool CanCreateDataSourceEnumerator => true;

        public override DbCommand CreateCommand()
        {
            if (ProviderConfig.m_bTraceLevelPublic)
            {
                Trace.Write(OracleTraceLevel.Public, OracleTraceTag.Entry, OracleTraceClassName.OracleClientFactory, OracleTraceFuncName.CreateCommand);
            }

            try
            {
                return new OracleCommand();
            }
            catch (Exception ex)
            {
                OracleException.HandleError(OracleTraceLevel.Public, OracleTraceTag.Error, OracleTraceClassName.OracleClientFactory, OracleTraceFuncName.CreateCommand, ex);
                throw;
            }
            finally
            {
                if (ProviderConfig.m_bTraceLevelPublic)
                {
                    Trace.Write(OracleTraceLevel.Public, OracleTraceTag.Exit, OracleTraceClassName.OracleClientFactory, OracleTraceFuncName.CreateCommand);
                }
            }
        }

        public override DbCommandBuilder CreateCommandBuilder()
        {
            if (ProviderConfig.m_bTraceLevelPublic)
            {
                Trace.Write(OracleTraceLevel.Public, OracleTraceTag.Entry, OracleTraceClassName.OracleClientFactory, OracleTraceFuncName.CreateCommandBuilder);
            }

            try
            {
                return new OracleCommandBuilder();
            }
            catch (Exception ex)
            {
                OracleException.HandleError(OracleTraceLevel.Public, OracleTraceTag.Error, OracleTraceClassName.OracleClientFactory, OracleTraceFuncName.CreateCommandBuilder, ex);
                throw;
            }
            finally
            {
                if (ProviderConfig.m_bTraceLevelPublic)
                {
                    Trace.Write(OracleTraceLevel.Public, OracleTraceTag.Exit, OracleTraceClassName.OracleClientFactory, OracleTraceFuncName.CreateCommandBuilder);
                }
            }
        }

        public override DbConnection CreateConnection()
        {
            if (ProviderConfig.m_bTraceLevelPublic)
            {
                Trace.Write(OracleTraceLevel.Public, OracleTraceTag.Entry, OracleTraceClassName.OracleClientFactory, OracleTraceFuncName.CreateConnection);
            }

            try
            {
                return new OracleConnection();
            }
            catch (Exception ex)
            {
                OracleException.HandleError(OracleTraceLevel.Public, OracleTraceTag.Error, OracleTraceClassName.OracleClientFactory, OracleTraceFuncName.CreateConnection, ex);
                throw;
            }
            finally
            {
                if (ProviderConfig.m_bTraceLevelPublic)
                {
                    Trace.Write(OracleTraceLevel.Public, OracleTraceTag.Exit, OracleTraceClassName.OracleClientFactory, OracleTraceFuncName.CreateConnection);
                }
            }
        }

        public override DbConnectionStringBuilder CreateConnectionStringBuilder()
        {
            if (ProviderConfig.m_bTraceLevelPublic)
            {
                Trace.Write(OracleTraceLevel.Public, OracleTraceTag.Entry, OracleTraceClassName.OracleClientFactory, OracleTraceFuncName.CreateConnectionStringBuilder);
            }

            try
            {
                return new OracleConnectionStringBuilder();
            }
            catch (Exception ex)
            {
                OracleException.HandleError(OracleTraceLevel.Public, OracleTraceTag.Error, OracleTraceClassName.OracleClientFactory, OracleTraceFuncName.CreateConnectionStringBuilder, ex);
                throw;
            }
            finally
            {
                if (ProviderConfig.m_bTraceLevelPublic)
                {
                    Trace.Write(OracleTraceLevel.Public, OracleTraceTag.Exit, OracleTraceClassName.OracleClientFactory, OracleTraceFuncName.CreateConnectionStringBuilder);
                }
            }
        }

        public override DbDataAdapter CreateDataAdapter()
        {
            if (ProviderConfig.m_bTraceLevelPublic)
            {
                Trace.Write(OracleTraceLevel.Public, OracleTraceTag.Entry, OracleTraceClassName.OracleClientFactory, OracleTraceFuncName.CreateDataAdapter);
            }

            try
            {
                return new OracleDataAdapter();
            }
            catch (Exception ex)
            {
                OracleException.HandleError(OracleTraceLevel.Public, OracleTraceTag.Error, OracleTraceClassName.OracleClientFactory, OracleTraceFuncName.CreateDataAdapter, ex);
                throw;
            }
            finally
            {
                if (ProviderConfig.m_bTraceLevelPublic)
                {
                    Trace.Write(OracleTraceLevel.Public, OracleTraceTag.Exit, OracleTraceClassName.OracleClientFactory, OracleTraceFuncName.CreateDataAdapter);
                }
            }
        }

        public override DbDataSourceEnumerator CreateDataSourceEnumerator()
        {
            if (ProviderConfig.m_bTraceLevelPublic)
            {
                Trace.Write(OracleTraceLevel.Public, OracleTraceTag.Entry, OracleTraceClassName.OracleClientFactory, OracleTraceFuncName.CreateDataSourceEnumerator);
            }

            try
            {
                return new OracleDataSourceEnumerator();
            }
            catch (Exception ex)
            {
                OracleException.HandleError(OracleTraceLevel.Public, OracleTraceTag.Error, OracleTraceClassName.OracleClientFactory, OracleTraceFuncName.CreateDataSourceEnumerator, ex);
                throw;
            }
            finally
            {
                if (ProviderConfig.m_bTraceLevelPublic)
                {
                    Trace.Write(OracleTraceLevel.Public, OracleTraceTag.Exit, OracleTraceClassName.OracleClientFactory, OracleTraceFuncName.CreateDataSourceEnumerator);
                }
            }
        }

        public override DbParameter CreateParameter()
        {
            if (ProviderConfig.m_bTraceLevelPublic)
            {
                Trace.Write(OracleTraceLevel.Public, OracleTraceTag.Entry, OracleTraceClassName.OracleClientFactory, OracleTraceFuncName.CreateParameter);
            }

            try
            {
                return new OracleParameter();
            }
            catch (Exception ex)
            {
                OracleException.HandleError(OracleTraceLevel.Public, OracleTraceTag.Error, OracleTraceClassName.OracleClientFactory, OracleTraceFuncName.CreateParameter, ex);
                throw;
            }
            finally
            {
                if (ProviderConfig.m_bTraceLevelPublic)
                {
                    Trace.Write(OracleTraceLevel.Public, OracleTraceTag.Exit, OracleTraceClassName.OracleClientFactory, OracleTraceFuncName.CreateParameter);
                }
            }
        }

        public override CodeAccessPermission CreatePermission(PermissionState state)
        {
            if (ProviderConfig.m_bTraceLevelPublic)
            {
                Trace.Write(OracleTraceLevel.Public, OracleTraceTag.Entry, OracleTraceClassName.OracleClientFactory, OracleTraceFuncName.CreatePermission);
            }

            try
            {
                return new OraclePermission(state);
            }
            catch (Exception ex)
            {
                OracleException.HandleError(OracleTraceLevel.Public, OracleTraceTag.Error, OracleTraceClassName.OracleClientFactory, OracleTraceFuncName.CreatePermission, ex);
                throw;
            }
            finally
            {
                if (ProviderConfig.m_bTraceLevelPublic)
                {
                    Trace.Write(OracleTraceLevel.Public, OracleTraceTag.Exit, OracleTraceClassName.OracleClientFactory, OracleTraceFuncName.CreatePermission);
                }
            }
        }
    }
}

当然，诸如 Mysql、DB2 等类同。由此可见，当后续新增数据库时，只需对 DbProviderFactory 抽象工厂进行继承即可，对已实现的数据工厂毫无影响。