How to Convert byte Array to IRandomAccessStream

UPDATE: For the RTM version you have to use SetSourceAsync method of the BitmapImage or WritableBitmap. A synchronous call just blocks the execution.

It seems to be a very common need among the Windows 8 (metro) developers to convert byte array to an IRandomAccessStream (i.e. when you want to set the source of a BitmapImage).

Here is what seems to work:

1) First we declare a wrapper class for a MemoryStream:

class MemoryRandomAccessStream : IRandomAccessStream
{
    private Stream m_InternalStream;

    public MemoryRandomAccessStream(Stream stream)
    {
        this.m_InternalStream = stream;
    }

    public MemoryRandomAccessStream(byte[] bytes)
    {
        this.m_InternalStream = new MemoryStream(bytes);
    }

    public IInputStream GetInputStreamAt(ulong position)
    {
        this.m_InternalStream.Seek((long)position, SeekOrigin.Begin);

        return this.m_InternalStream.AsInputStream();
    }

    public IOutputStream GetOutputStreamAt(ulong position)
    {
        this.m_InternalStream.Seek((long)position, SeekOrigin.Begin);

        return this.m_InternalStream.AsOutputStream();
    }

    public ulong Size
    {
        get { return (ulong)this.m_InternalStream.Length; }
        set { this.m_InternalStream.SetLength((long)value); }
    }

    public bool CanRead
    {
        get { return true; }
    }

    public bool CanWrite
    {
        get { return true; }
    }

    public IRandomAccessStream CloneStream()
    {
        throw new NotSupportedException();
    }

    public ulong Position
    {
        get { return (ulong)this.m_InternalStream.Position; }
    }

    public void Seek(ulong position)
    {
        this.m_InternalStream.Seek((long)position, 0);
    }

    public void Dispose()
    {
        this.m_InternalStream.Dispose();
    }

    public Windows.Foundation.IAsyncOperationWithProgress<IBuffer, uint> ReadAsync(IBuffer buffer, uint count, InputStreamOptions options)
    {
        var inputStream = this.GetInputStreamAt(0);
        return inputStream.ReadAsync(buffer, count, options);
    }

    public Windows.Foundation.IAsyncOperation<bool> FlushAsync()
    {
        var outputStream = this.GetOutputStreamAt(0);
        return outputStream.FlushAsync();
    }

    public Windows.Foundation.IAsyncOperationWithProgress<uint, uint> WriteAsync(IBuffer buffer)
    {
        var outputStream = this.GetOutputStreamAt(0);
        return outputStream.WriteAsync(buffer);
    }
}

2) Then you can either use an extension method that will convert the bytes or memory stream (i.e. public static IRandomAccessStream AsRandomAccessStream(this byte[] byteArray) ), or you can directly use this class to convert the byte array to IRandomAccessStream:

//
// We create the random access stream
MemoryStream stream = new MemoryStream(imageBytes);
var randomAccessStream = new MemoryRandomAccessStream(stream);

// or
// var randomAccessStream = new InMemoryRandomAccessStream(imageBytes);

BitmapImage bitmapImage = new BitmapImage();
bitmapImage.SetSourceAsync(randomAccessStream);
image.Source = bitmapImage;

Good luck everyone…