如何实现IInputStream UWP

using System;
using System.IO;
using System.Runtime.InteropServices.WindowsRuntime;
using System.Threading;
using System.Threading.Tasks;
using Windows.Storage.Streams;

public class CustomInputStream : IInputStream
{
    private MemoryStream inputStream;

    public CustomInputStream()
    {
        inputStream = new MemoryStream();
    }

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

    public async Task<int> ReadAsync(byte[] buffer, uint count, InputStreamOptions options, CancellationToken cancellationToken)
    {
        cancellationToken.ThrowIfCancellationRequested();

        return await inputStream.ReadAsync(buffer, 0, (int)count, cancellationToken);
    }

    public async Task<uint> ReadAsync(IBuffer buffer, uint count, InputStreamOptions options)
    {
        byte[] tempBuffer = new byte[count];
        int bytesRead = await inputStream.ReadAsync(tempBuffer, 0, (int)count);

        DataWriter writer = new DataWriter();
        writer.WriteBytes(tempBuffer);

        buffer.Length = (uint)bytesRead;
        writer.StoreAsync().GetResults();

        return (uint)bytesRead;
    }

    public async Task<bool> FlushAsync(CancellationToken cancellationToken)
    {
        cancellationToken.ThrowIfCancellationRequested();

        await inputStream.FlushAsync();
        return true;
    }

    public void Dispose()
    {
        inputStream.Dispose();
    }
}