C＃铸造的MemoryStream对FILESTREAM [英] C# Casting MemoryStream to FileStream

问题描述

我的代码是这样的：

byte[] byteArray = Encoding.ASCII.GetBytes(someText);
MemoryStream stream = new MemoryStream(byteArray);
StreamReader reader = new StreamReader(stream);
FileStream file = (FileStream)reader.BaseStream;

后来我用file.Name。

Later I'm using file.Name.

我收到一个InvalidCastException：它会显示如下

I'm getting an InvalidCastException: it displays follows

无法转换类型'System.IO.MemoryStream对象键入System.IO.FileStream。

Unable to cast object of type 'System.IO.MemoryStream' to type 'System.IO.FileStream'.

我读的地方，我应该只是改变的FileStream到流。有没有别的东西我应该怎么办？

I read somewhere that I should just change FileStream to Stream. Is there something else I should do?

推荐答案

A 的MemoryStream 未与文件相关联，并且没有一个文件名的概念。基本上，你不能这样做，

A MemoryStream is not associated with a file, and has no concept of a filename. Basically, you can't do that.

您当然不能施展它们之间;你只能施放一个向上向下 - 而不是横盘;可视化：

You certainly can't cast between them; you can only cast upwards an downwards - not sideways; to visualise:

        Stream
          |
   ---------------
   |             |
FileStream    MemoryStream

您可以施放一个的MemoryStream 到流平凡，和流到的MemoryStream 通过类型检查;但从来没有一个的FileStream 到的MemoryStream 。这好像是说狗是动物，大象是动物，所以我们可以投出狗大象。

You can cast a MemoryStream to a Stream trivially, and a Stream to a MemoryStream via a type-check; but never a FileStream to a MemoryStream. That is like saying a dog is an animal, and an elephant is an animal, so we can cast a dog to an elephant.

您的可以子类的MemoryStream 并添加名称属性（您提供一个值），但仍然没有共同性之间的的FileStream 和 YourCustomMemoryStream 和的FileStream 没有按' ŧ实施预先存在的界面获得名称;所以调用者就必须为明确分别处理两种，或者使用鸭打字（通过动态或反射可能）。

You could subclass MemoryStream and add a Name property (that you supply a value for), but there would still be no commonality between a FileStream and a YourCustomMemoryStream, and FileStream doesn't implement a pre-existing interface to get a Name; so the caller would have to explicitly handle both separately, or use duck-typing (maybe via dynamic or reflection).

另一种选择（也许更容易）可能是：将数据写入到一个临时文件;使用的FileStream 从那里;然后（后下）删除的文件。

Another option (perhaps easier) might be: write your data to a temporary file; use a FileStream from there; then (later) delete the file.

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