无法将源接口类型转换为目标接口类型

Question

我想要处理文件，因为它们保存在四个目录中，它们都以非常不同的方式处理。

我有一个通用的处理器IFileQueueService，它在调度定时器上运行，加载所有的文件名，并为每个文件调用一个自定义的处理器IExecutionProcessor。这可能是一个简单的问题，但我的处理器具有比标准IExecutionProvider更多的属性，并且我不确定如何调用这些自定义处理器。

//Basic processor interface
public interface IExecutionProvider
{
    void ProcessFile(string file);
}

//Simplified version of one of the custom processor interfaces
public interface IKyoExecutionProcessor
{
    string DestinationPath { get; set; }
}

public class KyoExecutionProcessor : IExecutionProvider, IKyoExecutionProcessor
{
   //This processor moves a file to the DestinationPath.
}

public interface IFileQueueService
{
    string SourcePath { get; set; }
    IExecutionProvider ExecutionProvider { get; set; }
    void Start();
    void Stop();
}

public class FileProcessor : IFileQueueService
{
    ...
    public virtual void ProcessFileQueue()
    {
        IEnumerable<string> filesToProcess = GetFilesReadyToProcess();
        foreach (string file in filesToProcess.ToList())
        {
            ExecutionProvider.ProcessFile(file);
        }
    }
}

public class KYOFileSysWatcher : ServiceBase
{
    private IFileQueueService Processor { get; set; }
    private IKyoExecutionProcessor KyoCustomProcessor { get; set; }

    public KYOFileSysWatcher()
    {
        Processor = ObjectFactory.GetInstance<IFileQueueService>();
        KyoCustomProcessor = ObjectFactory.GetInstance<IKyoExecutionProcessor>();

        //This doesn't work, cannot convert source type to target type, but it implements the IExecutionProvider interface??? How do I do this?
        Processor.ExecutionProvider = KyoCustomProcessor;

        Processor.Start(); //Sets up dispatch timer
    }

 }

Answer 1

泛型可以帮助你...

//Basic processor interface
public interface IExecutionProvider
{
    void ProcessFile(string file);
}

//Simplified version of one of the custom processor interfaces
public interface IKyoExecutionProcessor
{
    string DestinationPath { get; set; }
}

public interface IFileQueueService<TProvider>
    where TProvider : IExecutionProvider
{
    string SourcePath { get; set; }
    TProvider ExecutionProvider { get; set; }
    void Start();
    void Stop();
}

public class FileProcessor<TProvider> : IFileQueueService<TProvider>
    where TProvider : IExecutionProvider
{
    string[] GetFilesReadyToProcess() { return new string[0]; }
    public TProvider ExecutionProvider { get; set; }

    public virtual void ProcessFileQueue()
    {
        IEnumerable<string> filesToProcess = GetFilesReadyToProcess();
        foreach (string file in filesToProcess.ToList())
        {
            ExecutionProvider.ProcessFile(file);
        }
    }

    #region IFileQueueService<TProvider> Members

    public string SourcePath { get; set; }
    public void Start() { }
    public void Stop() { }

    #endregion
}

public class KyoExecutionProcessor : IExecutionProvider, IKyoExecutionProcessor
{
    //This processor moves a file to the DestinationPath.
    public string DestinationPath { get; set; }
    public void ProcessFile(string file) { }
}

public class ServiceBase<TProcessor>
    where TProcessor : IExecutionProvider
{
    protected FileProcessor<TProcessor> Processor { get; set; }
    protected TProcessor CustomProcessor { get; set; }
}

public class KYOFileSysWatcher : ServiceBase<KyoExecutionProcessor>
{
    public KYOFileSysWatcher()
    {
        Processor = ObjectFactory.GetInstance<FileProcessor<KyoExecutionProcessor>>();
        CustomProcessor = ObjectFactory.GetInstance<KyoExecutionProcessor>();

        //This compiles now!
        Processor.ExecutionProvider = CustomProcessor;

        Processor.Start(); //Sets up dispatch timer
    }
}

Answer 2

您的IKyoExecutionProcessor接口应该派生自IExecutionProvider，如下所示：

public interface IKyoExecutionProcessor : IExecutionProvider 
{
    string DestinationPath { get; set; }
}

这确保了接口之间存在' is -a‘关系，这也将使您能够像这样实现KyoExecutionProcessor类：

public class KyoExecutionProcessor : IKyoExecutionProcessor
{
   public void ProcessFile(string file) { ... }
   public string DestinationPath { get; set; }
}

这样，任何实现IKyoExecutionProcessor的对象都可以被赋值给IExecutionProvider类型的变量。

Processor.ExecutionProvider = KyoCustomProcessor; // You can now appoint IKyoExecutionProcessor instance to IExecutionProvider variable