如何在C＃中實現IRandomAccessStream？

Question

我想在C＃中實現一個IRandomAccessStream實例（它將返回實時生成的數據）。 該流實際上不需要是可寫的或可搜索的，但我想在ReadAsync方法中返回我自己的數據（它實際上是IInputStream一部分）。

public IAsyncOperationWithProgress<IBuffer, uint> ReadAsync(IBuffer buffer, uint count, InputStreamOptions options)
{
    throw new NotImplementedException("To be done");
}

我的兩個主要問題是：

1. 如何返回實現IAsyncOperationWithProgress ？ 框架中是否有任何內容可以幫助解決這個問題？
2. 如何將數據寫入緩沖區？ IBuffer只有Length和Capacity屬性（具體的Buffer類不再提供）。

Answer 1

如何將字節數組轉換為IRandomAccessStream

我發現這篇博客文章，希望這個IRandomAccessStream實現可以成為你的起點。

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);
     }
}

Answer 2

1. 使用AsyncInfo.Run(Func<CancellationToken, IProgress<uint>, Task<IBuffer>>)方法從委托創建IAsyncOperationWithProgress實例。

    public IAsyncOperationWithProgress<IBuffer, uint> ReadAsync(IBuffer buffer, uint count, InputStreamOptions options) { if (buffer == null) throw new ArgumentNullException("buffer"); Func<CancellationToken, IProgress<uint>, Task<IBuffer>> taskProvider = (token, progress) => ReadBytesAsync(buffer, count, token, progress, options); return AsyncInfo.Run(taskProvider); } private async Task<IBuffer> ReadBytesAsync(IBuffer buffer, uint count, CancellationToken token, IProgress<uint> progress, InputStreamOptions options) { ... Fill the buffer here. Report the progress. return buffer; } 

2. 通常，您不需要直接訪問緩沖區數據。 但是如果您需要在c＃中執行此操作，則可以使用System.Runtime.InteropServices.WindowsRuntime.WindowsRuntimeBufferExtensions類將數據復制到緩沖區或從緩沖區復制數據。