C++/CX 如何将 IRandomAccessStream^ 转换为字节并返回。 (UWP)

Question

所以我有一个流，我希望能够将它转换为 unsigned char * bytes 并返回可用流。

这个流是图片（重要的话是二进制的？）

基本上我现在的尝试是这样的：

IRandomAccessStream^ inputStream;

DataWriter^ dataWriter = ref new DataWriter(inputStream);
IBuffer^ buffer1 = dataWriter->DetachBuffer();
unsigned char * bytes = GetPointerToPixelData(buffer1);

DataWriter ^writer = ref new DataWriter();
writer->WriteBytes(Platform::ArrayReference<BYTE>(bytes, sizeof(bytes)));
task<DataWriterStoreOperation^>(writer->StoreAsync()).get();
task<Windows::Foundation::IAsyncOperation<bool>>(writer->FlushAsync()).get();

IBuffer ^buffer2 = writer->DetachBuffer();
IRandomAccessStream^ newStream;

task<Windows::Foundation::IAsyncOperationWithProgress<unsigned int, unsigned int>>(newStream->WriteAsync(buffer2)).get();
task<Windows::Foundation::IAsyncOperation<bool>>(newStream->FlushAsync()).get();
UseNewStream(newStream)

我已经添加了所有这些任务<...>，因为没有它们它就无法工作，而且我不确定如何让它工作？我在网上找到的函数 GetPointerToPixelData 如下：

byte* GetPointerToPixelData(IBuffer^ buffer)
{
    // Cast to Object^, then to its underlying IInspectable interface.

    Object^ obj = buffer;
    ComPtr<IInspectable> insp(reinterpret_cast<IInspectable*>(obj));

    // Query the IBufferByteAccess interface.
    ComPtr<IBufferByteAccess> bufferByteAccess;
    insp.As(&bufferByteAccess);

    // Retrieve the buffer data.

    byte* pixels = nullptr;
    bufferByteAccess->Buffer(&pixels);

    return pixels;
}

谢谢！ :)

Answer 1

首先，如果要将图像流转为字节，需要通过DataReader, not by DataWriter读取流，用于写数据。其次，DetachBuffer()方法是针对"Detaches the buffer that is associated with the data reader"的，不是读缓冲区。最后，DataReader可以直接用ReadBytes(Byte[])方法读取字节。例如：

uint64 length = 0; 
BYTE *extracted;
void CleanImagetobyte::MainPage::btnconverttobyte_Click(Platform::Object^ sender, Windows::UI::Xaml::RoutedEventArgs^ e)
{
    create_task(KnownFolders::GetFolderForUserAsync(nullptr /* current user */, KnownFolderId::PicturesLibrary))
        .then([this](StorageFolder^ picturesFolder)
    {
        return picturesFolder->GetFileAsync("B.jpg");
    }).then([this](task<StorageFile^> task)
    {
        try
        {
            StorageFile^ file = task.get();
            auto name = file->Name;
            return file->OpenAsync(FileAccessMode::Read);
        }
        catch (Exception^ e)
        {
            // I/O errors are reported as exceptions.
        }
    }).then([this](task<IRandomAccessStream^> task)
    {
        IRandomAccessStream^  inputStream = task.get();
        length = inputStream->Size;
        IBuffer^ buffer = ref new Buffer(inputStream->Size);
        inputStream->ReadAsync(buffer, inputStream->Size, InputStreamOptions::None);
        DataReader^ reader = DataReader::FromBuffer(buffer);
        extracted = new BYTE[buffer->Length]; 
        reader->ReadBytes(Platform::ArrayReference<BYTE>(extracted, buffer->Length)); 
    });
} 


void CleanImagetobyte::MainPage::btnconvertback_Click(Platform::Object^ sender, Windows::UI::Xaml::RoutedEventArgs^ e)
{ 
    create_task(KnownFolders::GetFolderForUserAsync(nullptr /* current user */, KnownFolderId::PicturesLibrary))
        .then([this](StorageFolder^ picturesFolder)
    {
        return picturesFolder->CreateFileAsync("newB.jpg", CreationCollisionOption::ReplaceExisting);
    }).then([this](task<StorageFile^> task)
    {
        StorageFile^ file = task.get();
        Array<byte>^ arr = ref new Array<byte>(extracted, length);
        FileIO::WriteBytesAsync(file, arr); 
    }); 
}

更详细的读写文件请参考this document。

C++/CX 如何将 IRandomAccessStream^ 转换为字节并返回。 (UWP)

C++/CX How to convert from IRandomAccessStream^ to bytes and back. (UWP)

c++

buffer

stream

c++-cx

uwp