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

Question

So I have a stream, what I want to be able is to transfer it into unsigned char * bytes and back to usable stream.
This stream is image (it is binary if it is important?)
Basically what I am trying now is as follows:
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)
I have added all of these task<...> because it is not working without them, and I am not sure how to make it work?
Function GetPointerToPixelData I found online and is following:
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;
}
Thanks! :)

Answer 1

Firstly, if you want to transfer the image stream to bytes, you need to read the stream by DataReader, not by DataWriter which is for write data. Secondly, the DetachBuffer() method is for "Detaches the buffer that is associated with the data reader", not read the buffer. Lastly, DataReader can directly read bytes by ReadBytes(Byte[]) method. For example:
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);
});
}
More details for read and write a file please reference this document.