DataReader Class

Definition

Namespace:

Windows.Storage.Streams

Reads data from an input stream.

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

Inheritance

Object Platform::Object IInspectable DataReader

Attributes

ActivatableAttribute ContractVersionAttribute MarshalingBehaviorAttribute ThreadingAttribute

Implements

IClosable IDisposable IDataReader

Windows requirements

Device family	Windows 10 (introduced in 10.0.10240.0)
API contract	Windows.Foundation.UniversalApiContract (introduced in v1.0)

Examples

The following code example shows how to write and read strings to an in-memory stream. For the full sample application in C# and in C++/CX, see Serializing and deserializing data sample.

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;
        }
    });
}

Remarks

Instances of DataReader objects do not support concurrent read operations. If an application concurrently reads or detaches a stream from a DataReader instance that is being read from, the call to the object will fail with the error HRESULT_FROM_WIN32(ERROR_INVALID_OPERATION).

Constructors

DataReader(IInputStream)

Creates and initializes a new instance of the data reader.

Properties

ByteOrder	Gets or sets the byte order of the data in the input stream.
InputStreamOptions	Gets or sets the read options for the input stream.
UnconsumedBufferLength	Gets the size of the buffer that has not been read.
UnicodeEncoding	Gets or sets the Unicode character encoding for the input stream.

Methods

Close()	Closes the current stream and releases system resources.
DetachBuffer()	Detaches the buffer that is associated with the data reader. This is useful if you want to retain the buffer after you dispose the data reader.
DetachStream()	Detaches the stream that is associated with the data reader.
Dispose()	Performs application-defined tasks associated with freeing, releasing, or resetting unmanaged resources.
FromBuffer(IBuffer)	Creates a new instance of the data reader with data from the specified buffer.
LoadAsync(UInt32)	Loads data from the input stream.
ReadBoolean()	Reads a Boolean value from the input stream.
ReadBuffer(UInt32)	Reads a buffer from the input stream.
ReadByte()	Reads a byte value from the input stream.
ReadBytes(Byte[])	Reads an array of byte values from the input stream.
ReadDateTime()	Reads a date and time value from the input stream.
ReadDouble()	Reads a floating-point value from the input stream.
ReadGuid()	Reads a GUID value from the input stream.
ReadInt16()	Reads a 16-bit integer value from the input stream.
ReadInt32()	Reads a 32-bit integer value from the input stream.
ReadInt64()	Reads a 64-bit integer value from the input stream.
ReadSingle()	Reads a floating-point value from the input stream.
ReadString(UInt32)	Reads a string value from the input stream.
ReadTimeSpan()	Reads a time-interval value from the input stream.
ReadUInt16()	Reads a 16-bit unsigned integer from the input stream.
ReadUInt32()	Reads a 32-bit unsigned integer from the input stream.
ReadUInt64()	Reads a 64-bit unsigned integer from the input stream.

See also

• DataReaderLoadOperation
• DataWriter
• Serializing and deserializing data sample (Windows 10)
• File access sample (Windows 10)
• StreamSocket sample (Windows 10)
• Custom USB device sample (Windows 10)
• DatagramSocket sample (Windows 10)