C++ task开启线程怎么做同步

Question

void DirectXPage::Init(Platform::String^ strType)
{
	OpenFile^ fopen = ref new  OpenFile();
	fopen->metro_fopen();

	fopen->localFile->Path; //异常,因为 fopen->metro_fopen() 里面是异步操作
}

我需要等待 StorageFile^ s2 =fopen->metro_fopen(); 执行完成，如果异步它会继续执行到 s2->Path; 导致异常

求助该怎么做同步，代码呈上，求指教。

fopen->metro_fopen() 

是个打开文件的操作：

StorageFile^ OpenFile::metro_fopen()
{

			FileOpenPicker^ picker = ref new FileOpenPicker();
			picker->SuggestedStartLocation = PickerLocationId::VideosLibrary;
			picker->FileTypeFilter->Append(".wmv");
			picker->FileTypeFilter->Append(".mp4");

			create_task(picker->PickSingleFileAsync()).then(
				[this](StorageFile^ inputFile)
			{
				
					localFile = inputFile; //取打开文件的 StorageFile 对象

					if(localFile != nullptr)
					{
						return inputFile->OpenAsync(FileAccessMode::Read);
					}
			}).then(
				[this](IRandomAccessStream^ inputStream)
			{
				
				}
			});
		}
	}
}