metro c++中各种流怎么转换啊？

Question

IBuffer^ 怎么转换为IRandomAccessStream，， IRandomAccessStream 怎么转换为IBuffer^？？？

Answer 1

File Access Sample C++ 版本有例子代码： http://code.msdn.microsoft.com/windowsapps/File-access-sample-d723e597  通过DataWriter 和 DataReader就可以做到：

IBuffer^ --> IRandomAccessStream

IBuffer^ buffer = ...;

task<IRandomAccessStream^>(file->OpenAsync(FileAccessMode::ReadWrite)).then([this, buffer](IRandomAccessStream^ stream)
{
    IOutputStream^ outputStream = stream->GetOutputStreamAt(0);			
    DataWriter^ dataWriter = ref new DataWriter(outputStream);
    dataWriter->WriteBuffer(buffer);
    ......
});

IRandomAccessStream --> IBuffer^

已删除错误代码.

modify to correct code:

	create_task(KnownFolders::DocumentsLibrary->GetFileAsync("test.txt")).then([this](IStorageFile^ file)
	{
		create_task(file->OpenAsync(FileAccessMode::Read)).then([this](IRandomAccessStream^ stream)
		{
			IInputStream^ inputStream = stream->GetInputStreamAt(0);
			DataReader^ dataReader = ref new DataReader(inputStream);
			create_task(dataReader->LoadAsync((unsigned int)stream->Size)).then([this,dataReader](unsigned int result)
			{
				IBuffer^ buffer = dataReader->DetachBuffer();
        ...
			});
		});
	});

论坛中还有一模一样问题的帖子：

• http://social.msdn.microsoft.com/Forums/zh-CN/metroappzhcn/thread/b26bb1fe-7671-41be-a49e-c223569d282f
• http://social.msdn.microsoft.com/Forums/zh-CN/metroappzhcn/thread/5242b502-9ed7-44c0-85f4-ca754c18ff1f
• http://social.msdn.microsoft.com/Forums/zh-CN/metroappzhcn/thread/4a28d90f-904e-437a-a930-501d2c83d2fb

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Bob Bao [MSFT]
MSDN Community Support | Feedback to us

Answer 2

IRandomAccessStream --> IBuffer^这个转换是不是有错啊。

    IInputStream^ inputStream = stream->GetInputStreamAt(0);
      DataReader^ dataReader = ref new DataReader(readStream);
      IBuffer^ buffer = dataReader->DetachBuffer();

inputStream 怎么都没用到呢？

Answer 3

reference to: http://social.msdn.microsoft.com/Forums/zh-CN/metroappzhcn/thread/8fa034b2-3149-4cff-a7ef-9c02235238b0

---

Bob Bao [MSFT]
MSDN Community Support | Feedback to us

Answer 4

又发现了一个问题，IBuffer^ --> IRandomAccessStream转换成功了,然后我让图片控件显示出来， 这时候，我想保持图片，保持不了。 如果不让图片显示出来，就是去掉以下代码：

      BitmapImage^ bitmapImage = ref new BitmapImage();
      bitmapImage->SetSource(randomAccessStream);this->image_Show->Source = bitmapImage;));

就可以保存成功了。请问一下，是不是因为让bitmapImage->SetSource（）。所以IRandomAccessStream就不能再用了？如果这时候，想通过IRandomAccessStream保存文件，有办法？谢谢

task<IRandomAccessStream^>(file->OpenAsync(FileAccessMode::ReadWrite)).then([this, buffer](IRandomAccessStream^ stream)
{
    IOutputStream^ outputStream = stream->GetOutputStreamAt(0);
    DataWriter^ dataWriter = ref new DataWriter(outputStream);
    dataWriter->WriteBuffer(buffer);

    task<unsigned int>(datawriter->StoreAsync()).then([this, randomAccessStream,_file,datawriter](unsigned int i){
       datawriter->FlushAsync();
      BitmapImage^ bitmapImage = ref new BitmapImage();
      bitmapImage->SetSource(randomAccessStream);
      this->image_Show->Source = bitmapImage;));

//用DataReader 把 IRandomAccessStream读取出来，然后保存。

DataReader^ dataReader = ref new DataReader(randomAccessStream);

.......
    ......
});