如何在StructureMap中动态创建对象的实例

Question

我有一个名为"ImportRunner"的抽象类。

我有一个名为"ScorecardRunner"的类的实现。

当我从XML文件中将对象类型作为字符串拉回来，并且它可以是ImportRunner的任何实现时，我如何在运行时获得ScorecardRunner之类的类的实例？

我当前的代码如下。

var importer = container.GetInstance<ImportRunner>();

当我尝试做下面这样的事情时，我会得到一个编译错误。

var importer = container.GetInstance<Type.GetType("Importer.ScorecardRunner")>();

运算符'<'不能应用于"method group"类型的操作数，并且"类型"

谢谢，Tom

Answer 1

与其分散基于运行时值创建实例的逻辑并将其硬插入StructureMap的注册表，不如简单地创建一个工厂来负责确定正确的runner实例并注入它。

例如：

public class XmlReader
{
    public bool IsScoreCard { get; set; }
}
public abstract class ImportRunner
{
}
public class ScorecardRunner : ImportRunner
{
}
public class DefaultRunner : ImportRunner
{
}
public class RunnerFactory
{
    private readonly XmlReader _reader;
    public RunnerFactory(XmlReader reader)
    {
        _reader = reader;
    }
    public ImportRunner Resolve()
    {
        if (_reader.IsScoreCard)
            return new ScorecardRunner();
        return new DefaultRunner();
    }
}

然后在注册表中这样配置：

this.For<ImportRunner>().Use(ctx => ctx.GetInstance<RunnerFactory>().Resolve());

Answer 2

很抱歉，但我不同意一般断言的答案。

如果你使用IoC，你不应该创建混凝土工厂。。。这就是依赖注入的全部意义。

考虑一下这个小例子

• UnitOfWork将由StructureMap实例化
• BankAccountApplication可以&也应该由StructureMap实例化

流程。BankAccounts库-示例类：
请注意应用程序类属性是如何引用UnitOfWork类的。

public class BankAccountApplication : IAccountApplication
{
    #region <Fields & Constants>
    private string StartingBalanceInvalidFormat = "A Starting Balance of {0} is invalid.";
    private string AnnualPercentageRateInvalidFormat = "The Annual Percentage Rate of {0} is invalid.";
    #endregion
    #region <Properties>
    [SetterProperty]
    public IDemoDbUnitOfWork UnitOfWork { get; set; }
    #endregion
    #region <Methods>
    public BankAccount CreateNew(AccountType bankAccountType, string ownerFullName, decimal startingBalance, decimal annualPercentageRate, string executedBy)
    {
        TraceHandler.TraceIn(TraceLevel.Info);
        if (string.IsNullOrWhiteSpace(ownerFullName))
            throw new ArgumentNullException("Owner Full Name");
        if (startingBalance < 0.0M)
            throw new ArgumentException(string.Format(StartingBalanceInvalidFormat, startingBalance));
        if (annualPercentageRate <= 0.0M)
            throw new ArgumentException(string.Format(AnnualPercentageRateInvalidFormat, annualPercentageRate));
        var account = new BankAccount();
        try
        {
            BankAccountType accountType = GetAccountType(bankAccountType);
            account.AnnualPercentageRate = annualPercentageRate;
            account.Balance = startingBalance;
            account.BankAccountTypeId = accountType.BankAccountTypeId;
            account.OwnerFullName = ownerFullName;
            account.ExecutedByName = executedBy;
            account.ExecutedDatetime = DateTime.UtcNow;
            UnitOfWork.BankAccounts.Add(account);
            UnitOfWork.SaveChanges();
        }
        catch (Exception ex)
        {
            TraceHandler.TraceError(ex);
        }
        finally
        {
            TraceHandler.TraceOut();
        }
        return account;
    }
    public IEnumerable<BankAccount> FindOverdrafts(IAccountAlgorithm overdraftAlgorithm)
    {
        TraceHandler.TraceIn(TraceLevel.Info);
        var accounts = new List<BankAccount>();
        try
        {
            var entities = UnitOfWork.BankAccounts.GetAll().ToList();
            entities.ForEach(e => {
                IAlgorithmResult calculation = overdraftAlgorithm.Calculate(e.Balance);
                if (calculation.Result)
                    accounts.Add(e);
            });
        }
        catch (Exception ex)
        {
            TraceHandler.TraceError(ex);
        }
        finally
        {
            TraceHandler.TraceOut();
        }
        return accounts.AsEnumerable();
    }
    private BankAccountType GetAccountType(AccountType bankAccountType)
    {
        var name = bankAccountType.ToStringValue();
        // In this case I am going to assume all accounts are properly mapped -> First()
        return UnitOfWork.BankAccountTypes.GetAll().Where(a => a.BankAccountTypeName == name).First();
    }
    #endregion
}

流程。BankAccounts库-ContainerRegistry:
此ContainerRegistry扫描程序集&"设置"根接口，然后使用命令获取更"明确"的指令。

public class ContainerRegistry : Registry
{
    #region <Constructors>
    public ContainerRegistry()
    {
        Scan(
            scan =>
            {
                scan.TheCallingAssembly();
                scan.WithDefaultConventions();
                scan.LookForRegistries();
                scan.AssembliesFromApplicationBaseDirectory(f => f.FullName.StartsWith("Bushido.Common", true, null));
                scan.AssembliesFromApplicationBaseDirectory(f => f.FullName.StartsWith("Bushido.Process", true, null));
                scan.AddAllTypesOf(typeof(IAccountApplication));
                scan.AddAllTypesOf(typeof(IAccountAlgorithm));
                scan.SingleImplementationsOfInterface();
            });
        ForSingletonOf(typeof(IDbContext)).Use(typeof(DemoDbContext));
        For(typeof(IDemoDbUnitOfWork)).Use(typeof(DemoDbUnitOfWork));
        For(typeof(IRepository<>)).Use(typeof(GenericRepository<>));
    }
    #endregion
}

UnitTest库-生成器：
当然，在单元测试中，您必须模拟第三方对象。但是你可以&应该使用IoC来完成。

    public partial class Builder
    {
        #region <Methods>
        public T CreateInstance<T>(IDemoDbUnitOfWork unitOfWork, bool byFullName = false)
        {
            if (unitOfWork == null)
                throw new ArgumentNullException("UnitOfWork");
            // Here, I am passing-in a MOCK of the UnitOfWork & "shimming" it into "T" via IoC
            var container = IoC.Initialize();
            container.Inject(typeof(IDemoDbUnitOfWork), unitOfWork);
            return container.GetInstance<T>();
        }
        public Mock<IDemoDbUnitOfWork> CreateMockUnitOfWork()
        {
            var unitOfWork = new Mock<IDemoDbUnitOfWork>();
            // DBO Tables
            var bankAccountRepository = BankAccountRepositoryBuilder.CreateMock();
            var bankAccountTypeRepository = BankAccountTypeRepositoryBuilder.CreateMock();
            unitOfWork.SetupAllProperties();
            // DBO Tables
            unitOfWork.SetupGet(x => x.BankAccounts).Returns(bankAccountRepository.Object);
            unitOfWork.SetupGet(x => x.BankAccountTypes).Returns(bankAccountTypeRepository.Object);
            return unitOfWork;
        }
        #endregion
    }

UnitTest库-测试：
现在，通过Builder类，您可以实例化您的类。。。因此，您可以很好地进行单元测试清理。

public void BankAccountApplication_CreateNew_Invalid_StartingBalance()
{
     // -----
     // ARRANGE
     var unitOfWork = Builder.CreateMockUnitOfWork();
     var application = Builder.CreateInstance<BankAccountApplication>(unitOfWork);
     // -----
     // ACT
     var account = application.CreateNew(AccountType.Checking, "Scrooge McDuck", -100.00M, 3.00M, Builder.ExecutedBy);
     // -----
     // ASSERT
     ...put your asserts here
}