Class / Action<T> 的构造函数？

Question

我有两个 class，它们都继承自 Stream class。

FirstClass : Stream 
{
    FirstClass(Stream, CompressionMode) 
    {
         ..
    } 
}

SecondClass : Stream 
{
    SecondClass(Stream, CompressionMode) 
    {
         ..
    } 
}

我想将其中一个 classes 放入一个变量（我猜是操作），然后从该变量创建一个新对象——像这样：

Action<Stream, CompressionMode> classPattern = condition ? FirstClass : SecondClass

///And now this
var newObject = classPattern(Stream, CompressionMode);

///Or maybe even this
classPattern newObject = classPattern(Stream, CompressionMode);

你好吗？

感谢帮助<3

Answer 1

看来，您需要一个带有两个参数的Func delegate

Func<Stream, CompressionMode, Stream> classPattern = (stream, mode) => condition ? (Stream)new FirstClass(stream, mode) : new SecondClass(stream, mode);

并使用它

var newObject = classPattern(stream, compressionMode);

您也可以将其转换为本地函数

Stream ClassPattern(Stream stream, CompressionMode mode) =>
    condition ? (Stream) new FirstClass(stream, mode) : new SecondClass(stream, mode);

Answer 2

我怀疑你是否真的想要这里的任何 lambda (Func<Stream, CompressionMode, Stream>)。如果你有很多模式、条件、选项，labda 将太复杂而无法维护。我建议 factory class:

public static class MyClassBuilder {
  public static Stream Create(Stream parent, CompressionMode mode) {
    // Note, that we can easily include validation into factory's method  
    if (null == parent)
      throw new ArgumentNullException(nameof(parent));

    return condition(mode, parent)  
      ? new FirstClass(parent, mode)
      : new SecondClass(parent, mode);
  }

  // It's easy to implement building with default mode:
  public static Stream Create(Stream parent, CompressionMode mode) =>
    Create(parent, CompressionMode.MaximumCompression);  
}

.....

var newObject = MyClassBuilder.Create(someStream, someCompressionMode);

// with default CompressionMode
var otherObject = MyClassBuilder.Create(someOtherStream);

Class / Action<T> 的构造函数？

Class / constructor to Action<T>?

c#

generics

constructor

delegates

class