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。