DataReader 类

定义

命名空间:

Windows.Storage.Streams

从输入流读取数据。

public ref class DataReader sealed : IClosable, IDataReader

/// [Windows.Foundation.Metadata.ContractVersion(Windows.Foundation.UniversalApiContract, 65536)]
/// [Windows.Foundation.Metadata.MarshalingBehavior(Windows.Foundation.Metadata.MarshalingType.Agile)]
/// [Windows.Foundation.Metadata.Threading(Windows.Foundation.Metadata.ThreadingModel.Both)]
/// [Windows.Foundation.Metadata.Activatable(Windows.Storage.Streams.IDataReaderFactory, 65536, "Windows.Foundation.UniversalApiContract")]
class DataReader final : IClosable, IDataReader

[Windows.Foundation.Metadata.ContractVersion(typeof(Windows.Foundation.UniversalApiContract), 65536)]
[Windows.Foundation.Metadata.MarshalingBehavior(Windows.Foundation.Metadata.MarshalingType.Agile)]
[Windows.Foundation.Metadata.Threading(Windows.Foundation.Metadata.ThreadingModel.Both)]
[Windows.Foundation.Metadata.Activatable(typeof(Windows.Storage.Streams.IDataReaderFactory), 65536, "Windows.Foundation.UniversalApiContract")]
public sealed class DataReader : System.IDisposable, IDataReader

function DataReader(inputStream)

Public NotInheritable Class DataReader
Implements IDataReader, IDisposable

继承

Object Platform::Object IInspectable DataReader

属性

ActivatableAttribute ContractVersionAttribute MarshalingBehaviorAttribute ThreadingAttribute

实现

IClosable IDisposable IDataReader

Windows 要求

设备系列	Windows 10 (在 10.0.10240.0 中引入)
API contract	Windows.Foundation.UniversalApiContract (在 v1.0 中引入)

示例

下面的代码示例演示如何向内存中流写入和读取字符串。 有关 C# 和 C++/CX 中的完整示例应用程序，请参阅 序列化和反序列化数据示例。

using System;
using System.Diagnostics;
using Windows.Foundation;
using Windows.UI.Xaml;
using Windows.UI.Xaml.Controls;
using Windows.UI.Xaml.Navigation;

// This is the click handler for the 'Copy Strings' button.  Here we will parse the
// strings contained in the ElementsToWrite text block, write them to a stream using
// DataWriter, retrieve them using DataReader, and output the results in the
// ElementsRead text block.
private async void TransferData(object sender, RoutedEventArgs e)
{
    // Initialize the in-memory stream where data will be stored.
    using (var stream = new Windows.Storage.Streams.InMemoryRandomAccessStream())
    {
        // Create the data writer object backed by the in-memory stream.
        using (var dataWriter = new Windows.Storage.Streams.DataWriter(stream))
        {
            dataWriter.UnicodeEncoding = Windows.Storage.Streams.UnicodeEncoding.Utf8;
            dataWriter.ByteOrder = Windows.Storage.Streams.ByteOrder.LittleEndian;

            // Parse the input stream and write each element separately.
            string[] inputElements = ElementsToWrite.Text.Split(';');
            foreach (string inputElement in inputElements)
            {
                uint inputElementSize = dataWriter.MeasureString(inputElement);
                dataWriter.WriteUInt32(inputElementSize);
                dataWriter.WriteString(inputElement);
            }

            // Send the contents of the writer to the backing stream.
            await dataWriter.StoreAsync();

            // For the in-memory stream implementation we are using, the flushAsync call 
            // is superfluous,but other types of streams may require it.
            await dataWriter.FlushAsync();

            // In order to prolong the lifetime of the stream, detach it from the 
            // DataWriter so that it will not be closed when Dispose() is called on 
            // dataWriter. Were we to fail to detach the stream, the call to 
            // dataWriter.Dispose() would close the underlying stream, preventing 
            // its subsequent use by the DataReader below.
            dataWriter.DetachStream();
        }

        // Create the input stream at position 0 so that the stream can be read 
        // from the beginning.
        using (var inputStream = stream.GetInputStreamAt(0))
        {
            using (var dataReader = new Windows.Storage.Streams.DataReader(inputStream))
            {
                // The encoding and byte order need to match the settings of the writer 
                // we previously used.
                dataReader.UnicodeEncoding = Windows.Storage.Streams.UnicodeEncoding.Utf8;
                dataReader.ByteOrder = Windows.Storage.Streams.ByteOrder.LittleEndian;

                // Once we have written the contents successfully we load the stream.
                await dataReader.LoadAsync((uint)stream.Size);

                var receivedStrings = "";

                // Keep reading until we consume the complete stream.
                while (dataReader.UnconsumedBufferLength > 0)
                {
                    // Note that the call to readString requires a length of "code units" 
                    // to read. This is the reason each string is preceded by its length 
                    // when "on the wire".
                    uint bytesToRead = dataReader.ReadUInt32();
                    receivedStrings += dataReader.ReadString(bytesToRead) + "\n";
                }

                // Populate the ElementsRead text block with the items we read 
                // from the stream.
                ElementsRead.Text = receivedStrings;
            }
        }
    }
}

#include "pch.h"
#include "WriteReadStream.h" // header file for WriteReadStream.xaml.
#include <sstream>

#include <winrt/Windows.Foundation.h>
#include <winrt/Windows.Storage.Streams.h>

using namespace winrt;

std::array<winrt::hstring, 5> m_inputElements{ L"Hello", L"World", L"1 2 3 4 5", L"Très bien!", L"Goodbye" };

WriteReadStream::WriteReadStream()
{
    InitializeComponent();

    // Populate the text block with the input elements.
    std::wstringstream stringstream;
    for (winrt::hstring const& element : m_inputElements)
    {
        stringstream << element.c_str() << L";";
    }
    ElementsToWrite().Text(stringstream.str().c_str());
}

// This is the click handler for the 'Copy Strings' button. Here we will parse the
// strings contained in the ElementsToWrite text block, write them to a stream using
// DataWriter, retrieve them using DataReader, and output the results in the
// ElementsRead text block.
winrt::Windows::Foundation::IAsyncAction WriteReadStream::TransferData(
    Windows::Foundation::IInspectable const& /* sender */,
    Windows::UI::Xaml::RoutedEventArgs const& /* args */)
{
    // Initialize the in-memory stream where data will be stored.
    Windows::Storage::Streams::InMemoryRandomAccessStream stream;

    // Create the DataWriter object backed by the in-memory stream. When
    // dataWriter goes out of scope, it closes the underlying stream.
    Windows::Storage::Streams::DataWriter dataWriter{ stream };
    dataWriter.UnicodeEncoding(Windows::Storage::Streams::UnicodeEncoding::Utf16LE);
    dataWriter.ByteOrder(Windows::Storage::Streams::ByteOrder::LittleEndian);

    // Create the data reader by using the input stream set at position 0 so that 
    // the stream will be read from the beginning regardless of the position that
    // the original stream ends up in after the store.
    Windows::Storage::Streams::IInputStream inputStream{ stream.GetInputStreamAt(0) };
    Windows::Storage::Streams::DataReader dataReader{ inputStream };
    // The encoding and byte order need to match the settings of the writer that
    // we previously used.
    dataReader.UnicodeEncoding(Windows::Storage::Streams::UnicodeEncoding::Utf16LE);
    dataReader.ByteOrder(Windows::Storage::Streams::ByteOrder::LittleEndian);

    // Write the input data to the output stream. Serialize the elements by writing
    // each string separately, preceded by its length in bytes.
    for (winrt::hstring const& element : m_inputElements)
    {
        dataWriter.WriteUInt32(element.size());
        dataWriter.WriteString(element);
    }

    // Send the contents of the writer to the backing stream.
    unsigned int bytesStored{ co_await dataWriter.StoreAsync() };

    // For the in-memory stream implementation we are using, the FlushAsync() call 
    // is superfluous, but other types of streams may require it.
    if (co_await dataWriter.FlushAsync())
    {
        try
        {
            // Once we've written the contents successfully, we load the stream.
            unsigned int bytesLoaded{ co_await dataReader.LoadAsync((unsigned int)stream.Size()) };

            std::wstringstream readFromStream;

            // Keep reading until we consume the complete stream.
            while (dataReader.UnconsumedBufferLength() > 0)
            {
                // Note that the call to ReadString requires a length of 
                // "code units" to read. This is the reason each string is 
                // preceded by its length when "on the wire".
                unsigned int bytesToRead{ dataReader.ReadUInt32() };
                readFromStream << dataReader.ReadString(bytesToRead).c_str() << std::endl;
            }

            // Populate the ElementsRead text block with the items we read from the stream
            ElementsRead().Text(readFromStream.str().c_str());
        }
        catch (winrt::hresult_error const& ex)
        {
            ElementsRead().Text(L"Error: " + ex.message());
        }
    }
}

#include "pch.h"
#include "WriteReadStream.xaml.h"

using namespace Concurrency;
using namespace DataReaderWriter;
using namespace Platform;
using namespace Windows::Storage::Streams;
using namespace Windows::UI::Xaml;
using namespace Windows::UI::Xaml::Controls;
using namespace Windows::UI::Xaml::Navigation;

Array<String^>^ _inputElements = ref new Array<String^>
{
    "Hello", "World", "1 2 3 4 5", "Très bien!", "Goodbye"
};

WriteReadStream::WriteReadStream()
{
    InitializeComponent();

    // Populate the text block with the input elements.
    ElementsToWrite->Text = "";
    for (unsigned int i = 0; i < _inputElements->Length; i++)
    {
        ElementsToWrite->Text += _inputElements[i] + ";";
    }
}

// Invoked when this page is about to be displayed in a Frame.
void WriteReadStream::OnNavigatedTo(NavigationEventArgs^ e)
{
    // Get a pointer to our main page.
    rootPage = MainPage::Current;
}

// This is the click handler for the 'Copy Strings' button.  Here we will parse the
// strings contained in the ElementsToWrite text block, write them to a stream using
// DataWriter, retrieve them using DataReader, and output the results in the
// ElementsRead text block.
void DataReaderWriter::WriteReadStream::TransferData(
Platform::Object^ sender, Windows::UI::Xaml::RoutedEventArgs^ e)
{
    // Initialize the in-memory stream where data will be stored.
    InMemoryRandomAccessStream^ stream = ref new InMemoryRandomAccessStream();

    // Create the DataWriter object backed by the in-memory stream.  When
    // dataWriter is deleted, it will also close the underlying stream.
    DataWriter^ dataWriter = ref new DataWriter(stream);
    dataWriter->UnicodeEncoding = UnicodeEncoding::Utf8;
    dataWriter->ByteOrder = ByteOrder::LittleEndian;

    // Create the data reader by using the input stream set at position 0 so that 
    // the stream will be read from the beginning regardless of where the position
    // the original stream ends up in after the store.
    IInputStream^ inputStream = stream->GetInputStreamAt(0);
    DataReader^ dataReader = ref new DataReader(inputStream);
    // The encoding and byte order need to match the settings of the writer 
    // we previously used.
    dataReader->UnicodeEncoding = UnicodeEncoding::Utf8;
    dataReader->ByteOrder = ByteOrder::LittleEndian;

    // Write the input data to the output stream.  Serialize the elements by writing
    // each string separately, preceded by its length.
    for (unsigned int i = 0; i < _inputElements->Length; i++) 
    {
        unsigned int inputElementSize = dataWriter->MeasureString(_inputElements[i]);
        dataWriter->WriteUInt32(inputElementSize);
        dataWriter->WriteString(_inputElements[i]);
    }

    // Send the contents of the writer to the backing stream.
    create_task(dataWriter->StoreAsync()).then([this, dataWriter] (unsigned int bytesStored)
    {
        // For the in-memory stream implementation we are using, the FlushAsync() call 
        // is superfluous, but other types of streams may require it.
        return dataWriter->FlushAsync();
    }).then([this, dataReader, stream] (bool flushOp)
    {
        // Once we have written the contents successfully we load the stream.
        return dataReader->LoadAsync((unsigned int) stream->Size);
    }).then([this, dataReader] (task<unsigned int> bytesLoaded)
    {
        try
        {
            // Check for possible exceptions that could have been thrown 
            // in the async call chain.
            bytesLoaded.get();

            String^ readFromStream = "";

            // Keep reading until we consume the complete stream.
            while (dataReader->UnconsumedBufferLength > 0)
            {
                // Note that the call to ReadString requires a length of 
                // "code units" to read. This is the reason each string is 
                // preceded by its length when "on the wire".
                unsigned int bytesToRead = dataReader->ReadUInt32();
                readFromStream += dataReader->ReadString(bytesToRead) + "\n";
            }

            // Populate the ElementsRead text block with the items we read from the stream
            ElementsRead->Text = readFromStream;
        }
        catch (Exception^ e)
        {
            ElementsRead->Text = "Error: " + e->Message;
        }
    });
}

注解

DataReader 对象的实例不支持并发读取操作。 如果应用程序从要从中读取的 DataReader 实例并发读取或分离流，则对对象的调用将失败并出现错误HRESULT_FROM_WIN32 (ERROR_INVALID_OPERATION) 。

构造函数

DataReader(IInputStream)

创建并初始化数据读取器的新实例。

属性

ByteOrder	获取或设置输入流中数据的字节顺序。
InputStreamOptions	获取或设置输入流的读取选项。
UnconsumedBufferLength	获取尚未读取的缓冲区的大小。
UnicodeEncoding	获取或设置输入流的 Unicode 字符编码。

方法

Close()	关闭当前流并释放系统资源。
DetachBuffer()	分离与数据读取器关联的缓冲区。 如果要在释放数据读取器后保留缓冲区，这非常有用。
DetachStream()	分离与数据读取器关联的流。
Dispose()	执行与释放或重置非托管资源关联的应用程序定义的任务。
FromBuffer(IBuffer)	使用指定缓冲区中的数据创建数据读取器的新实例。
LoadAsync(UInt32)	从输入流加载数据。
ReadBoolean()	从输入流中读取布尔值。
ReadBuffer(UInt32)	从输入流中读取缓冲区。
ReadByte()	从输入流中读取字节值。
ReadBytes(Byte[])	从输入流中读取字节值的数组。
ReadDateTime()	从输入流中读取日期和时间值。
ReadDouble()	从输入流中读取浮点值。
ReadGuid()	从输入流中读取 GUID 值。
ReadInt16()	从输入流中读取 16 位整数值。
ReadInt32()	从输入流中读取 32 位整数值。
ReadInt64()	从输入流中读取 64 位整数值。
ReadSingle()	从输入流中读取浮点值。
ReadString(UInt32)	从输入流中读取字符串值。
ReadTimeSpan()	从输入流中读取时间间隔值。
ReadUInt16()	从输入流中读取 16 位无符号整数。
ReadUInt32()	从输入流中读取 32 位无符号整数。
ReadUInt64()	从输入流中读取 64 位无符号整数。

另请参阅

• DataReaderLoadOperation
• DataWriter
• 序列化和反序列化数据示例 (Windows 10)
• 文件访问示例 (Windows 10)
• StreamSocket 示例 (Windows 10)
• 自定义 USB 设备示例 (Windows 10)
• DatagramSocket 示例 (Windows 10)