如何从windows8商店应用程序中的字节数组中获取流

Question

I have been trying get a stream from a byte array in metro style app using the following code.

InMemoryRandomAccessStream memoryStream = new InMemoryRandomAccessStream();
memoryStream.AsStreamForWrite().Write(byteArray, 0, byteArray.Length);
memoryStream.Seek(0);

It executes with no errors but stream size is zero (0). Can anybody tell me why is its size is zero?

Answer 1

You can use the DataWriter and DataReader classes. For example ...

// put bytes into the stream
var ms = new InMemoryRandomAccessStream();
var dw = new Windows.Storage.Streams.DataWriter(ms);
dw.WriteBytes(new byte[] { 0x00, 0x01, 0x02 });
await dw.StoreAsync();

// read them out
ms.Seek(0);
byte[] ob = new byte[ms.Size];
var dr = new Windows.Storage.Streams.DataReader(ms);
await dr.LoadAsync((uint)ms.Size);
dr.ReadBytes(ob);

Answer 2

You can also use the BinaryWriter/BinaryReader to read and write from and to byte[] and Streams.

    private Stream ConvertToStream(byte[] raw)
    {
        Stream streamOutput = new MemoryStream();
        using (BinaryWriter writer = new BinaryWriter(streamOutput))
        {
            writer.Write(raw);
        }
        return streamOutput;
    }

Another option is to use built in extension methods as Marc Gravell already mentioned:

    private Stream ConvertToStream(byte[] raw)
    {
        return raw.AsBuffer().AsStream();
    }

The extension methods are commented with [Security Critical] which may indicate a later change. However, after looking around a bit I couldn't find any additional information on the security code comment.

Answer 3

I know this is a very old question, but I was running into this issue myself today and figured it out so I'll leave this here for others.

I realized that the stream wasn't being written if it was too small. To fix this, I explicitly set the length of the stream like this:

ms.AsStreamForWrite(imageBytes.Length).Write(imageBytes, 0, imageBytes.Length);

That should be all you need.