How to write IntPtr to a file in UWP

Question

I'm trying to report a bug of a MP3 decoder and the developer asked me to generate the PCM file for him to identify the problem.

So this is the code I used to generate the PCM file

private async Task NewMethod()
    {
        var file = await SelectPlaybackFile();
        await Task.Run(() =>
        {
            _handle = Bass.BASS_StreamCreateFile(file.Path, 0,0,BASSFlag.BASS_STREAM_AUTOFREE | BASSFlag.BASS_SAMPLE_FLOAT);
            var _myDSPProc = new DSPPROC(Dsp1);
            int dspHandle = Bass.BASS_ChannelSetDSP(_handle, _myDSPProc, IntPtr.Zero, 0);

            Bass.BASS_ChannelPlay(_handle, false);
        });

    }

    unsafe void Dsp1(int handle, int channel, IntPtr buffer, int length, IntPtr user)
    {
    }

I notice the buffer is a unmanaged memory and I never dealt with it before. So I started doing some research and found a answer here and this is the code from that answer

private void callback(IntPtr buffer, int length)
{
    FileStream file = new FileStream(filename, FileMode.Create, FileAccess.Write);
    int written;
    WriteFile(file.Handle, buffer, length, out written, IntPtr.Zero);
    file.Close();
}

 [DllImport("kernel32.dll")]
 private static extern bool WriteFile(IntPtr hFile, IntPtr lpBuffer, int NumberOfBytesToWrite, out int lpNumberOfBytesWritten, IntPtr lpOverlapped);

However, the code above might not be working on UWP since the app is running in a sandbox and dev cannot access to path.

Is there any other way to help write a IntPtr to a file in UWP?

Answer 1

In UWP app you can access certain file system locations by default see the File access permissions document.

You can try the following code.

private async void Method(IntPtr buffer, int length)
{
    StorageFile file = await ApplicationData.Current.LocalFolder.CreateFileAsync("MyFile.txt", CreationCollisionOption.ReplaceExisting);
    var stream = await file.OpenAsync(FileAccessMode.ReadWrite, StorageOpenOptions.AllowReadersAndWriters);
    unsafe
    {
        UnmanagedMemoryStream ustream = new UnmanagedMemoryStream((byte*)buffer, length);
        ustream.CopyTo(stream.AsStream());
        ustream.Dispose();
        stream.Dispose();
    }
}

Note: in Visual Studio, you should select the Allow unsafe code configuration.(Right click your project=>Select Build tab=>Select Allow unsafe code).