Panduan: Koneksi Menggunakan Tugas dan Permintaan HTTP XML

  • Artikel

Contoh ini memperlihatkan cara menggunakan antarmuka IXMLHTTPRequest2 dan IXMLHTTPRequest2Callback bersama dengan tugas untuk mengirim permintaan HTTP GET dan POST ke layanan web di aplikasi Platform Windows Universal (UWP). Dengan menggabungkan IXMLHTTPRequest2 bersama dengan tugas, Anda dapat menulis kode yang menyusun dengan tugas lain. Misalnya, Anda dapat menggunakan tugas unduhan sebagai bagian dari rantai tugas. Tugas pengunduhan juga dapat merespons saat pekerjaan dibatalkan.

Tip

Anda juga dapat menggunakan C++ REST SDK untuk melakukan permintaan HTTP dari aplikasi UWP menggunakan aplikasi C++ atau dari aplikasi C++ desktop. Untuk informasi selengkapnya, lihat C++ REST SDK (Codename "Casablanca").

Untuk informasi selengkapnya tentang tugas, lihat Paralelisme Tugas. Untuk informasi selengkapnya tentang cara menggunakan tugas di aplikasi UWP, lihat Pemrograman asinkron di C++ dan Membuat Operasi Asinkron di C++ untuk Aplikasi UWP.

Dokumen ini pertama-tama menunjukkan cara membuat HttpRequest dan kelas pendukungnya. Kemudian menunjukkan cara menggunakan kelas ini dari aplikasi UWP yang menggunakan C++ dan XAML.

Untuk contoh yang menggunakan IXMLHTTPRequest2 tetapi tidak menggunakan tugas, lihat Mulai Cepat: Koneksi menggunakan Permintaan HTTP XML (IXMLHTTPRequest2).

Tip

IXMLHTTPRequest2 dan IXMLHTTPRequest2Callback adalah antarmuka yang kami rekomendasikan untuk digunakan dalam aplikasi UWP. Anda juga dapat menyesuaikan contoh ini untuk digunakan di aplikasi desktop.

Prasyarat

Dukungan UWP bersifat opsional di Visual Studio 2017 dan yang lebih baru. Untuk menginstalnya, buka Penginstal Visual Studio dari Windows menu Mulai dan pilih versi Visual Studio yang Anda gunakan. Klik tombol Ubah dan pastikan petak peta Pengembangan UWP dicentang. Di bawah Komponen Opsional pastikan bahwa Alat UWP C++ dicentang. Gunakan v141 untuk Visual Studio 2017 atau v142 untuk Visual Studio 2019.

Menentukan Kelas HttpRequest, HttpRequestBuffersCallback, dan HttpRequestStringCallback

Saat Anda menggunakan IXMLHTTPRequest2 antarmuka untuk membuat permintaan web melalui HTTP, Anda menerapkan IXMLHTTPRequest2Callback antarmuka untuk menerima respons server dan bereaksi terhadap peristiwa lain. Contoh ini mendefinisikan HttpRequest kelas untuk membuat permintaan web, dan HttpRequestBuffersCallback kelas dan HttpRequestStringCallback untuk memproses respons. Kelas HttpRequestBuffersCallback dan HttpRequestStringCallback mendukung HttpRequest kelas; Anda hanya bekerja dengan HttpRequest kelas dari kode aplikasi.

Metode GetAsync, PostAsync kelas HttpRequest memungkinkan Anda untuk memulai operasi HTTP GET dan POST, masing-masing. Metode ini menggunakan HttpRequestStringCallback kelas untuk membaca respons server sebagai string. Metode SendAsync dan ReadAsync memungkinkan Anda mengalirkan konten besar dalam gugus. Metode ini setiap mengembalikan konkurensi::task untuk mewakili operasi. Metode GetAsync dan PostAsync menghasilkan task<std::wstring> nilai, di wstring mana bagian mewakili respons server. Metode SendAsync dan ReadAsync menghasilkan task<void> nilai; tugas-tugas ini selesai ketika operasi kirim dan baca selesai.

IXMLHTTPRequest2 Karena antarmuka bertindak secara asinkron, contoh ini menggunakan konkurensi::task_completion_event untuk membuat tugas yang selesai setelah objek panggilan balik selesai atau membatalkan operasi pengunduhan. Kelas HttpRequest membuat kelanjutan berbasis tugas dari tugas ini untuk mengatur hasil akhir. Kelas HttpRequest menggunakan kelanjutan berbasis tugas untuk memastikan bahwa tugas kelanjutan berjalan meskipun tugas sebelumnya menghasilkan kesalahan atau dibatalkan. Untuk informasi selengkapnya tentang kelanjutan berbasis tugas, lihat Paralelisme Tugas

Untuk mendukung pembatalan, HttpRequestkelas , HttpRequestBuffersCallback, dan HttpRequestStringCallback menggunakan token pembatalan. Kelas HttpRequestBuffersCallback dan HttpRequestStringCallback menggunakan metode konkurensi::cancellation_token::register_callback untuk mengaktifkan peristiwa penyelesaian tugas untuk merespons pembatalan. Panggilan balik pembatalan ini membatalkan unduhan. Untuk informasi selengkapnya tentang pembatalan, lihat Pembatalan.

Untuk Menentukan Kelas HttpRequest

  1. Dari menu utama, pilih File>Proyek Baru.>

  2. Gunakan templat Aplikasi Kosong C++ (Universal Windows) untuk membuat proyek aplikasi XAML kosong. Contoh ini menamai proyek UsingIXMLHTTPRequest2.

  3. Tambahkan ke proyek file header yang diberi nama HttpRequest.h dan file sumber yang bernama HttpRequest.cpp.

  4. Di pch.h, tambahkan kode ini:

    #include <ppltasks.h>
#include <string>
#include <sstream>
#include <wrl.h>
#include <msxml6.h>

  5. Di HttpRequest.h, tambahkan kode ini:

    #pragma once
#include "pch.h"

inline void CheckHResult(HRESULT hResult)
{
    if (hResult == E_ABORT)
    {
        concurrency::cancel_current_task();
    }
    else if (FAILED(hResult))
    {
        throw Platform::Exception::CreateException(hResult);
    }
}

namespace Web
{

namespace Details
{

// Implementation of IXMLHTTPRequest2Callback used when partial buffers are needed from the response.
// When only the complete response is needed, use HttpRequestStringCallback instead.
class HttpRequestBuffersCallback 
    : public Microsoft::WRL::RuntimeClass<
        Microsoft::WRL::RuntimeClassFlags<Microsoft::WRL::ClassicCom>,
        IXMLHTTPRequest2Callback,
        Microsoft::WRL::FtmBase>
{
public:
    HttpRequestBuffersCallback(IXMLHTTPRequest2* httpRequest, 
        concurrency::cancellation_token ct = concurrency::cancellation_token::none()) :
        request(httpRequest), cancellationToken(ct), responseReceived(false), dataHResult(S_OK), statusCode(200)
    {
        // Register a callback function that aborts the HTTP operation when 
        // the cancellation token is canceled.
        if (cancellationToken != concurrency::cancellation_token::none())
        {
            registrationToken = cancellationToken.register_callback([this]() 
            {
                if (request != nullptr) 
                {
                    request->Abort();
                }
            });
        }

        dataEvent = concurrency::task_completion_event<void>();
    }

    // Called when the HTTP request is being redirected to a new URL.
    IFACEMETHODIMP OnRedirect(IXMLHTTPRequest2*, PCWSTR) 
    {
        return S_OK;
    }

    // Called when HTTP headers have been received and processed.
    IFACEMETHODIMP OnHeadersAvailable(IXMLHTTPRequest2*, DWORD statusCode, PCWSTR reasonPhrase)
    {
        HRESULT hr = S_OK;

        // We must not propagate exceptions back to IXHR2.
        try
        {
            this->statusCode = statusCode;
            this->reasonPhrase = reasonPhrase;

            concurrency::critical_section::scoped_lock lock(dataEventLock);
            dataEvent.set();
        }
        catch (std::bad_alloc&)
        {
            hr = E_OUTOFMEMORY;
        }
        return hr;
    }

    // Called when a portion of the entity body has been received.
    IFACEMETHODIMP OnDataAvailable(IXMLHTTPRequest2*, ISequentialStream* stream)
    {
        HRESULT hr = S_OK;

        // We must not propagate exceptions back to IXHR2.
        try
        {
            // Store a reference on the stream so it can be accessed by the task.
            dataStream = stream;

            // The work must be done as fast as possible, and must not block this thread,
            // for example, waiting on another event object.  Here we simply set an event
            // that can be processed by another thread.
            concurrency::critical_section::scoped_lock lock(dataEventLock);
            dataEvent.set();
        }
        catch (std::bad_alloc&)
        {
            hr = E_OUTOFMEMORY;
        }
        return hr;
    }
        
    // Called when the entire entity response has been received.
    IFACEMETHODIMP OnResponseReceived(IXMLHTTPRequest2* xhr, ISequentialStream* responseStream)
    {
        responseReceived = true;
        return OnDataAvailable(xhr, responseStream);
    }
        
    // Called when an error occurs during the HTTP request.
    IFACEMETHODIMP OnError(IXMLHTTPRequest2*, HRESULT hrError) 
    {
        HRESULT hr = S_OK;

        // We must not propagate exceptions back to IXHR2.
        try
        {
            concurrency::critical_section::scoped_lock lock(dataEventLock);
            dataHResult = hrError;
            dataEvent.set();
        }
        catch (std::bad_alloc&)
        {
            hr = E_OUTOFMEMORY;
        }

        return hr;
    }

    // Create a task that completes when data is available, in an exception-safe way.
    concurrency::task<void> CreateDataTask();

    HRESULT GetError() const
    {
        return dataHResult;
    }

    int GetStatusCode() const
    {
        return statusCode;
    }

    std::wstring const& GetReasonPhrase() const
    {
        return reasonPhrase;
    }

    bool IsResponseReceived() const
    {
        return responseReceived;
    }

    // Copy bytes from the sequential stream into the buffer provided until
    // we reach the end of one or the other.
    unsigned int ReadData(
        _Out_writes_(outputBufferSize) byte* outputBuffer,
        unsigned int outputBufferSize);

private:
    ~HttpRequestBuffersCallback()
    {
        // Unregister the callback.
        if (cancellationToken != concurrency::cancellation_token::none())
        {
            cancellationToken.deregister_callback(registrationToken);
        }
    }

    // Signals that the download operation was canceled.
    concurrency::cancellation_token cancellationToken;

    // Used to unregister the cancellation token callback.
    concurrency::cancellation_token_registration registrationToken;

    // The IXMLHTTPRequest2 that processes the HTTP request.
    Microsoft::WRL::ComPtr<IXMLHTTPRequest2> request;
    
    // Task completion event that is set when data is available or error is triggered.
    concurrency::task_completion_event<void> dataEvent;
    concurrency::critical_section dataEventLock;

    // We cannot store the error obtained from IXHR2 in the dataEvent since any value there is first-writer-wins,
    // whereas we want a subsequent error to override an initial success.
    HRESULT dataHResult;

    // Referenced pointer to the data stream.
    Microsoft::WRL::ComPtr<ISequentialStream> dataStream;

    // HTTP status code and reason returned by the server.
    int statusCode;
    std::wstring reasonPhrase;

    // Whether the response has been completely received.
    bool responseReceived;
};

};

// Utility class for performing asynchronous HTTP requests.
// This class only supports one outstanding request at a time.
class HttpRequest
{
public:
    HttpRequest();

    int GetStatusCode() const
    {
        return statusCode;
    }

    std::wstring const& GetReasonPhrase() const
    {
        return reasonPhrase;
    }

    // Whether the response has been completely received, if using ReadAsync().
    bool IsResponseComplete() const
    {
        return responseComplete;
    }

    // Start an HTTP GET on the specified URI.  The returned task completes once the entire response
    // has been received, and the task produces the HTTP response text.  The status code and reason
    // can be read with GetStatusCode() and GetReasonPhrase().
    concurrency::task<std::wstring> GetAsync(
        Windows::Foundation::Uri^ uri, 
        concurrency::cancellation_token cancellationToken = concurrency::cancellation_token::none());

    // Start an HTTP POST on the specified URI, using a string body.  The returned task produces the 
    // HTTP response text.  The status code and reason can be read with GetStatusCode() and GetReasonPhrase().
    concurrency::task<std::wstring> PostAsync(
        Windows::Foundation::Uri^ uri,
        PCWSTR contentType,
        IStream* postStream,
        uint64 postStreamSizeToSend,
        concurrency::cancellation_token cancellationToken = concurrency::cancellation_token::none());

    // Start an HTTP POST on the specified URI, using a stream body.  The returned task produces the
    // HTTP response text.  The status code and reason can be read with GetStatusCode() and GetReasonPhrase().
    concurrency::task<std::wstring> PostAsync(
        Windows::Foundation::Uri^ uri,
        const std::wstring& str,
        concurrency::cancellation_token cancellationToken = concurrency::cancellation_token::none());

    // Send a request but don't return the response.  Instead, let the caller read it with ReadAsync().
    concurrency::task<void> SendAsync(
        const std::wstring& httpMethod,
        Windows::Foundation::Uri^ uri,
        concurrency::cancellation_token cancellationToken = concurrency::cancellation_token::none());

    // Read a chunk of data from the HTTP response, up to a specified length or until we reach the end
    // of the response, and store the value in the provided buffer.  This is useful for large content,
    // enabling the streaming of the result.
    concurrency::task<void> ReadAsync(
        Windows::Storage::Streams::IBuffer^ readBuffer,
        unsigned int offsetInBuffer,
        unsigned int requestedBytesToRead);

    static void CreateMemoryStream(IStream **stream);

private:
    // Start a download of the specified URI using the specified method.  The returned task produces the
    // HTTP response text.  The status code and reason can be read with GetStatusCode() and GetReasonPhrase().
    concurrency::task<std::wstring> DownloadAsync(
        PCWSTR httpMethod,
        PCWSTR uri, 
        concurrency::cancellation_token cancellationToken,
        PCWSTR contentType,
        IStream* postStream,
        uint64 postStreamBytesToSend);

    // Referenced pointer to the callback, if using SendAsync/ReadAsync.
    Microsoft::WRL::ComPtr<Details::HttpRequestBuffersCallback> buffersCallback;

    int statusCode;
    std::wstring reasonPhrase;

    // Whether the response has been completely received, if using ReadAsync().
    bool responseComplete;
};

};

  6. Di HttpRequest.cpp, tambahkan kode ini:

    #include "pch.h"
#include "HttpRequest.h"
#include <robuffer.h>
#include <shcore.h>

using namespace concurrency;
using namespace Microsoft::WRL;
using namespace Platform;
using namespace std;
using namespace Web;
using namespace Windows::Foundation;
using namespace Windows::Storage::Streams;

// Implementation of IXMLHTTPRequest2Callback used when only the complete response is needed.
// When processing chunks of response data as they are received, use HttpRequestBuffersCallback instead.
class HttpRequestStringCallback 
    : public RuntimeClass<RuntimeClassFlags<ClassicCom>, IXMLHTTPRequest2Callback, FtmBase>
{
public:
    HttpRequestStringCallback(IXMLHTTPRequest2* httpRequest, 
        cancellation_token ct = concurrency::cancellation_token::none()) :
        request(httpRequest), cancellationToken(ct)
    {
        // Register a callback function that aborts the HTTP operation when 
        // the cancellation token is canceled.
        if (cancellationToken != cancellation_token::none())
        {
            registrationToken = cancellationToken.register_callback([this]() 
            {
                if (request != nullptr) 
                {
                    request->Abort();
                }
            });
        }
    }

    // Called when the HTTP request is being redirected to a new URL.
    IFACEMETHODIMP OnRedirect(IXMLHTTPRequest2*, PCWSTR) 
    {
        return S_OK;
    }

    // Called when HTTP headers have been received and processed.
    IFACEMETHODIMP OnHeadersAvailable(IXMLHTTPRequest2*, DWORD statusCode, PCWSTR reasonPhrase)
    {
        HRESULT hr = S_OK;

        // We must not propagate exceptions back to IXHR2.
        try
        {
            this->statusCode = statusCode;
            this->reasonPhrase = reasonPhrase;
        }
        catch (std::bad_alloc&)
        {
            hr = E_OUTOFMEMORY;
        }

        return hr;
    }

    // Called when a portion of the entity body has been received.
    IFACEMETHODIMP OnDataAvailable(IXMLHTTPRequest2*, ISequentialStream*)
    {
        return S_OK;
    }
        
    // Called when the entire entity response has been received.
    IFACEMETHODIMP OnResponseReceived(IXMLHTTPRequest2*, ISequentialStream* responseStream)
    {
        wstring wstr;
        HRESULT hr = ReadUtf8StringFromSequentialStream(responseStream, wstr);

        // We must not propagate exceptions back to IXHR2.
        try
        {
            completionEvent.set(make_tuple<HRESULT, wstring>(move(hr), move(wstr)));
        }
        catch (std::bad_alloc&)
        {
            hr = E_OUTOFMEMORY;
        }

        return hr;
    }

    // Simulate the functionality of DataReader.ReadString().
    // This is needed because DataReader requires IRandomAccessStream and this
    // code has an ISequentialStream that does not have a conversion to IRandomAccessStream like IStream does.
    HRESULT ReadUtf8StringFromSequentialStream(ISequentialStream* readStream, wstring& str)
    {
        // Convert the response to Unicode wstring.
        HRESULT hr;

        // Holds the response as a Unicode string.
        wstringstream ss;

        while (true)
        {
            ULONG cb;
            char buffer[4096];

            // Read the response as a UTF-8 string.  Since UTF-8 characters are 1-4 bytes long,
            // we need to make sure we only read an integral number of characters.  So we'll
            // start with 4093 bytes.
            hr = readStream->Read(buffer, sizeof(buffer) - 3, &cb);
            if (FAILED(hr) || (cb == 0))
            {
                break; // Error or no more data to process, exit loop.
            }

            if (cb == sizeof(buffer) - 3)
            {
                ULONG subsequentBytesRead;
                unsigned int i, cl;

                // Find the first byte of the last UTF-8 character in the buffer.
                for (i = cb - 1; (i >= 0) && ((buffer[i] & 0xC0) == 0x80); i--);

                // Calculate the number of subsequent bytes in the UTF-8 character.
                if (((unsigned char)buffer[i]) < 0x80)
                {
                    cl = 1;
                }
                else if (((unsigned char)buffer[i]) < 0xE0)
                {
                    cl = 2;
                }
                else if (((unsigned char)buffer[i]) < 0xF0)
                {
                    cl = 3;
                }
                else
                {
                    cl = 4;
                }

                // Read any remaining bytes.
                if (cb < i + cl)
                {
                    hr = readStream->Read(buffer + cb, i + cl - cb, &subsequentBytesRead);
                    if (FAILED(hr))
                    {
                        break; // Error, exit loop.
                    }
                    cb += subsequentBytesRead;
                }
            }

            // First determine the size required to store the Unicode string.
            int const sizeRequired = MultiByteToWideChar(CP_UTF8, 0, buffer, cb, nullptr, 0);
            if (sizeRequired == 0)
            {
                // Invalid UTF-8.
                hr = HRESULT_FROM_WIN32(GetLastError());
                break;
            }
            unique_ptr<char16[]> wstr(new(std::nothrow) char16[sizeRequired + 1]);
            if (wstr.get() == nullptr)
            {
                hr = E_OUTOFMEMORY;
                break;
            }

            // Convert the string from UTF-8 to UTF-16LE.  This can never fail, since
            // the previous call above succeeded.
            MultiByteToWideChar(CP_UTF8, 0, buffer, cb, wstr.get(), sizeRequired);
            wstr[sizeRequired] = L'\0'; // Terminate the string.
            ss << wstr.get(); // Write the string to the stream.
        }

        str = SUCCEEDED(hr) ? ss.str() : wstring();
        return (SUCCEEDED(hr)) ? S_OK : hr; // Don't return S_FALSE.
    }
        
    // Called when an error occurs during the HTTP request.
    IFACEMETHODIMP OnError(IXMLHTTPRequest2*, HRESULT hrError) 
    {
        HRESULT hr = S_OK;

        // We must not propagate exceptions back to IXHR2.
        try
        {
            completionEvent.set(make_tuple<HRESULT, wstring>(move(hrError), wstring()));
        }
        catch (std::bad_alloc&)
        {
            hr = E_OUTOFMEMORY;
        }

        return hr;
    }

    // Retrieves the completion event for the HTTP operation.
    task_completion_event<tuple<HRESULT, wstring>> const& GetCompletionEvent() const
    {
        return completionEvent; 
    }

    int GetStatusCode() const
    {
        return statusCode;
    }

    wstring GetReasonPhrase() const
    {
        return reasonPhrase;
    }

private:
    ~HttpRequestStringCallback()
    {
        // Unregister the callback.
        if (cancellationToken != cancellation_token::none())
        {
            cancellationToken.deregister_callback(registrationToken);
        }
    }

    // Signals that the download operation was canceled.
    cancellation_token cancellationToken;

    // Used to unregister the cancellation token callback.
    cancellation_token_registration registrationToken;

    // The IXMLHTTPRequest2 that processes the HTTP request.
    ComPtr<IXMLHTTPRequest2> request;

    // Task completion event that is set when the 
    // download operation completes.
    task_completion_event<tuple<HRESULT, wstring>> completionEvent;

    int statusCode;
    wstring reasonPhrase;
};

// Copy bytes from the sequential stream into the buffer provided until
// we reach the end of one or the other.
unsigned int Web::Details::HttpRequestBuffersCallback::ReadData(
    _Out_writes_(outputBufferSize) byte* outputBuffer,
    unsigned int outputBufferSize)
{
    // Lock the data event while doing the read, to ensure that any bytes we don't read will
    // result in the correct event getting triggered.
    concurrency::critical_section::scoped_lock lock(dataEventLock);

    ULONG bytesRead;
    CheckHResult(dataStream.Get()->Read(outputBuffer, outputBufferSize, &bytesRead));
    if (bytesRead < outputBufferSize)
    {
        // We need to reset the data event, which we can only do by creating a new one.
        dataEvent = task_completion_event<void>();
    }

    return bytesRead;
}

// Create a task that completes when data is available, in an exception-safe way.
task<void> Web::Details::HttpRequestBuffersCallback::CreateDataTask()
{
    concurrency::critical_section::scoped_lock lock(dataEventLock);
    return create_task(dataEvent, cancellationToken);
}

HttpRequest::HttpRequest() : responseComplete(true), statusCode(200)
{
}

// Start a download of the specified URI using the specified method.  The returned task produces the
// HTTP response text.  The status code and reason can be read with GetStatusCode() and GetReasonPhrase().
task<wstring> HttpRequest::DownloadAsync(PCWSTR httpMethod, PCWSTR uri, cancellation_token cancellationToken,
    PCWSTR contentType, IStream* postStream, uint64 postStreamSizeToSend)
{
    // Create an IXMLHTTPRequest2 object.
    ComPtr<IXMLHTTPRequest2> xhr;
    CheckHResult(CoCreateInstance(CLSID_XmlHttpRequest, nullptr, CLSCTX_INPROC, IID_PPV_ARGS(&xhr)));

    // Create callback.
    auto stringCallback = Make<HttpRequestStringCallback>(xhr.Get(), cancellationToken);
    CheckHResult(stringCallback ? S_OK : E_OUTOFMEMORY);

    auto completionTask = create_task(stringCallback->GetCompletionEvent());

    // Create a request.
    CheckHResult(xhr->Open(httpMethod, uri, stringCallback.Get(), nullptr, nullptr, nullptr, nullptr));

    if (postStream != nullptr && contentType != nullptr)
    {
        CheckHResult(xhr->SetRequestHeader(L"Content-Type", contentType));
    }

    // Send the request.
    CheckHResult(xhr->Send(postStream, postStreamSizeToSend));

    // Return a task that completes when the HTTP operation completes. 
    // We pass the callback to the continuation because the lifetime of the 
    // callback must exceed the operation to ensure that cancellation 
    // works correctly.
    return completionTask.then([this, stringCallback](tuple<HRESULT, wstring> resultTuple)
    {
        // If the GET operation failed, throw an Exception.
        CheckHResult(std::get<0>(resultTuple));

        statusCode = stringCallback->GetStatusCode();
        reasonPhrase = stringCallback->GetReasonPhrase();

        return std::get<1>(resultTuple);
    });
}

// Start an HTTP GET on the specified URI.  The returned task completes once the entire response
// has been received, and the task produces the HTTP response text.  The status code and reason
// can be read with GetStatusCode() and GetReasonPhrase().
task<wstring> HttpRequest::GetAsync(Uri^ uri, cancellation_token cancellationToken)
{
    return DownloadAsync(L"GET",
                         uri->AbsoluteUri->Data(),
                         cancellationToken,
                         nullptr,
                         nullptr,
                         0);
}

void HttpRequest::CreateMemoryStream(IStream **stream)
{
    auto randomAccessStream = ref new Windows::Storage::Streams::InMemoryRandomAccessStream();
    CheckHResult(CreateStreamOverRandomAccessStream(randomAccessStream, IID_PPV_ARGS(stream)));
}

// Start an HTTP POST on the specified URI, using a string body.  The returned task produces the
// HTTP response text.  The status code and reason can be read with GetStatusCode() and GetReasonPhrase().
task<wstring> HttpRequest::PostAsync(Uri^ uri, const wstring& body, cancellation_token cancellationToken)
{
    int length = 0;
    ComPtr<IStream> postStream;
    CreateMemoryStream(&postStream);

    if (body.length() > 0)
    {
        // Get the required buffer size.
        int size = WideCharToMultiByte(CP_UTF8,                         // UTF-8
                                       0,                               // Conversion type
                                       body.c_str(),                    // Unicode string to convert
                                       static_cast<int>(body.length()), // Size
                                       nullptr,                         // Output buffer
                                       0,                               // Output buffer size
                                       nullptr,
                                       nullptr);
        CheckHResult((size != 0) ? S_OK : HRESULT_FROM_WIN32(GetLastError()));

        std::unique_ptr<char[]> tempData(new char[size]);
        length = WideCharToMultiByte(CP_UTF8,                         // UTF-8
                                     0,                               // Conversion type
                                     body.c_str(),                    // Unicode string to convert
                                     static_cast<int>(body.length()), // Size
                                     tempData.get(),                  // Output buffer
                                     size,                            // Output buffer size
                                     nullptr,
                                     nullptr);
        CheckHResult((length != 0) ? S_OK : HRESULT_FROM_WIN32(GetLastError()));
        CheckHResult(postStream->Write(tempData.get(), length, nullptr));
    }

    return DownloadAsync(L"POST",
                         uri->AbsoluteUri->Data(),
                         cancellationToken,
                         L"text/plain;charset=utf-8",
                         postStream.Get(),
                         length);
}

// Start an HTTP POST on the specified URI, using a stream body.  The returned task produces the
// HTTP response text.  The status code and reason can be read with GetStatusCode() and GetReasonPhrase().
task<wstring> HttpRequest::PostAsync(Uri^ uri, PCWSTR contentType, IStream* postStream,
    uint64 postStreamSizeToSend, cancellation_token cancellationToken)
{
    return DownloadAsync(L"POST",
                         uri->AbsoluteUri->Data(),
                         cancellationToken,
                         contentType,
                         postStream,
                         postStreamSizeToSend);
}

// Send a request but don't return the response.  Instead, let the caller read it with ReadAsync().
task<void> HttpRequest::SendAsync(const wstring& httpMethod, Uri^ uri, cancellation_token cancellationToken)
{
    // Create an IXMLHTTPRequest2 object.
    ComPtr<IXMLHTTPRequest2> xhr;
    CheckHResult(CoCreateInstance(CLSID_XmlHttpRequest, nullptr, CLSCTX_INPROC, IID_PPV_ARGS(&xhr)));

    // Create callback.
    buffersCallback = Make<Web::Details::HttpRequestBuffersCallback>(xhr.Get(), cancellationToken);
    CheckHResult(buffersCallback ? S_OK : E_OUTOFMEMORY);

    ComPtr<IXMLHTTPRequest2Callback> xhrCallback;
    CheckHResult(buffersCallback.As(&xhrCallback));

    // Open and send the request.
    CheckHResult(xhr->Open(httpMethod.c_str(),
                           uri->AbsoluteUri->Data(),
                           xhrCallback.Get(),
                           nullptr,
                           nullptr,
                           nullptr,
                           nullptr));

    responseComplete = false;

    CheckHResult(xhr->Send(nullptr, 0));

    // Return a task that completes when the HTTP operation completes.
    // Since buffersCallback holds a reference on the callback, the lifetime of the callback will exceed
    // the operation and ensure that cancellation works correctly.
    return buffersCallback->CreateDataTask().then([this]()
    {
        CheckHResult(buffersCallback->GetError());

        statusCode = buffersCallback->GetStatusCode();
        reasonPhrase = buffersCallback->GetReasonPhrase();
    });
}

// Read a chunk of data from the HTTP response, up to a specified length or until we reach the end
// of the response, and store the value in the provided buffer.  This is useful for large content,
// enabling the streaming of the result.
task<void> HttpRequest::ReadAsync(Windows::Storage::Streams::IBuffer^ readBuffer, unsigned int offsetInBuffer,
    unsigned int requestedBytesToRead)
{
    if (offsetInBuffer + requestedBytesToRead > readBuffer->Capacity)
    {
        throw ref new InvalidArgumentException();
    }

    // Return a task that completes when a read completes. 
    // We pass the callback to the continuation because the lifetime of the 
    // callback must exceed the operation to ensure that cancellation 
    // works correctly.
    return buffersCallback->CreateDataTask().then([this, readBuffer, offsetInBuffer, requestedBytesToRead]()
    {
        CheckHResult(buffersCallback->GetError());

        // Get a pointer to the location to copy data into.
        ComPtr<IBufferByteAccess> bufferByteAccess;
        CheckHResult(reinterpret_cast<IUnknown*>(readBuffer)->QueryInterface(IID_PPV_ARGS(&bufferByteAccess)));
        byte* outputBuffer; // Returned internal pointer, do not free this value.
        CheckHResult(bufferByteAccess->Buffer(&outputBuffer));

        // Copy bytes from the sequential stream into the buffer provided until
        // we reach the end of one or the other.
        readBuffer->Length = buffersCallback->ReadData(outputBuffer + offsetInBuffer, requestedBytesToRead);
        if (buffersCallback->IsResponseReceived() && (readBuffer->Length < requestedBytesToRead))
        {
            responseComplete = true;
        }
    });
}

Menggunakan Kelas HttpRequest di Aplikasi UWP

Bagian ini menunjukkan cara menggunakan HttpRequest kelas di aplikasi UWP. Aplikasi ini menyediakan kotak input yang menentukan sumber daya URL, dan perintah tombol yang melakukan operasi GET dan POST, dan perintah tombol yang membatalkan operasi saat ini.

Untuk Menggunakan Kelas HttpRequest

  1. Di MainPage.xaml, tentukan elemen StackPanel sebagai berikut.

    <StackPanel HorizontalAlignment="Left" Width="440"
            Background="{StaticResource ApplicationPageBackgroundThemeBrush}">
    <TextBox x:Name="InputTextBox" TextWrapping="Wrap" 
             Text="http://www.fourthcoffee.com/"/>
    <StackPanel Orientation="Horizontal">
        <Button x:Name="GetButton" Content="Get" Background="Green" 
            Click="GetButton_Click"/>
        <Button x:Name="PostButton" Content="Post" Background="Blue" 
            Click="PostButton_Click"/>
        <Button x:Name="CancelButton" Content="Cancel" Background="Red"
            IsEnabled="False" Click="CancelButton_Click"/>
        <ProgressRing x:Name="ResponseProgressRing" />
    </StackPanel>
    <TextBlock x:Name="ResponseTextBlock" TextWrapping="Wrap"/>
</StackPanel>

  2. Di MainPage.xaml.h, tambahkan direktif ini #include :

    #include "HttpRequest.h"

  3. Di MainPage.xaml.h, tambahkan variabel anggota ini private ke MainPage kelas :

    // Produces HTTP requets.
Web::HttpRequest m_httpRequest;
// Enables us to cancel the active HTTP request.
concurrency::cancellation_token_source m_cancelHttpRequestSource;

  4. Dalam MainPage.xaml.h, deklarasikan private metode ProcessHttpRequest:

    // Displays the result of the provided HTTP request on the UI.
void ProcessHttpRequest(concurrency::task<std::wstring> httpRequest);

  5. Di MainPage.xaml.cpp, tambahkan pernyataan ini using :

    using namespace concurrency;
using namespace std;
using namespace Web;

  6. Di MainPage.xaml.cpp, terapkan GetButton_Clickmetode , PostButton_Click, dan CancelButton_Click kelas MainPage .

    void MainPage::GetButton_Click(Object^ sender, RoutedEventArgs^ e)
{
    // Create a new cancellation token source for the web request.
    m_cancelHttpRequestSource = cancellation_token_source();

    // Set up the GET request parameters.
    auto uri = ref new Uri(InputTextBox->Text);
    auto token = m_cancelHttpRequestSource.get_token();

    // Send the request and then update the UI.
    ProcessHttpRequest(m_httpRequest.GetAsync(uri, token));
}

void MainPage::PostButton_Click(Object^ sender, RoutedEventArgs^ e)
{
    // Create a new cancellation token source for the web request.
    m_cancelHttpRequestSource = cancellation_token_source();

    // Set up the POST request parameters.
    auto uri = ref new Uri(InputTextBox->Text);
    wstring postData(L"This is sample POST data.");
    auto token = m_cancelHttpRequestSource.get_token();

    // Send the request and then update the UI.
    ProcessHttpRequest(m_httpRequest.PostAsync(uri, postData, token));
}

void MainPage::CancelButton_Click(Object^ sender, RoutedEventArgs^ e)
{
    // Disable the Cancel button.
    // It will be re-enabled during the next web request.
    CancelButton->IsEnabled = false;

    // Initiate cancellation.
    m_cancelHttpRequestSource.cancel();
}

    Tip

    Jika aplikasi Anda tidak memerlukan dukungan untuk pembatalan, berikan konkurensi::cancellation_token::none ke HttpRequest::GetAsync metode dan HttpRequest::PostAsync .

  7. Di MainPage.xaml.cpp, terapkan metode .MainPage::ProcessHttpRequest

    // Displays the result of the provided HTTP request on the UI.
void MainPage::ProcessHttpRequest(task<wstring> httpRequest)
{
    // Enable only the Cancel button.
    GetButton->IsEnabled = false;
    PostButton->IsEnabled = false;
    CancelButton->IsEnabled = true;

    // Clear the previous response and start the progress ring.
    ResponseTextBlock->Text = "";
    ResponseProgressRing->IsActive = true;

    // Create a continuation that shows the results on the UI.
    // The UI must be updated on the ASTA thread. 
    // Therefore, schedule the continuation to run on the current context.
    httpRequest.then([this](task<wstring> previousTask)
    {
        try
        {
            //
            // Show the result on the UI.

            wstring response = previousTask.get();
            if (m_httpRequest.GetStatusCode() == 200)
            {
                // The request succeeded. Show the response.
                ResponseTextBlock->Text = ref new String(response.c_str());
            }
            else
            {
                // The request failed. Show the status code and reason.
                wstringstream ss;
                ss << L"The server returned "
                   << m_httpRequest.GetStatusCode()
                   << L" ("
                   << m_httpRequest.GetReasonPhrase()
                   << L')';
                ResponseTextBlock->Text = ref new String(ss.str().c_str());
            }
        }
        catch (const task_canceled&)
        {
            // Indicate that the operation was canceled.
            ResponseTextBlock->Text = "The operation was canceled";
        }
        catch (Exception^ e)
        {
            // Indicate that the operation failed.
            ResponseTextBlock->Text = "The operation failed";

            // TODO: Handle the error further.
            (void)e;
        }

        // Enable the Get and Post buttons.
        GetButton->IsEnabled = true;
        PostButton->IsEnabled = true;
        CancelButton->IsEnabled = false;

        // Stop the progress ring.
        ResponseProgressRing->IsActive = false;

    }, task_continuation_context::use_current());
}

  8. Di properti proyek, di bawah Linker, Input, tentukan shcore.lib dan msxml6.lib.

Berikut adalah aplikasi yang sedang berjalan:

The running Windows Runtime app.

Langkah berikutnya

Panduan Runtime Konkurensi

Baca juga

Paralelisme Tugas
Pembatalan di PPL
Pemrograman asinkron di C++
Membuat Operasi Asinkron di C++ untuk Aplikasi UWP
Mulai cepat: Koneksi menggunakan Xml HTTP Request (IXMLHTTPRequest2)task Class (Concurrency Runtime)
Kelas task_completion_event