public static Task<Stream> OpenStreamForWriteAsync(this IStorageFolder rootDirectory, string relativePath, CreationCollisionOption creationCollisionOption)
{
#if WINDOWS_UWP || WINDOWS_APP || WINDOWS_PHONE_APP || WINDOWS_PHONE
return WindowsRuntimeStorageExtensions.OpenStreamForWriteAsync((global::Windows.Storage.StorageFolder)((StorageFolder)rootDirectory), relativePath, (global::Windows.Storage.CreationCollisionOption)((int)creationCollisionOption));
#elif __ANDROID__ || __UNIFIED__ || WIN32
string newPath = Path.Combine(rootDirectory.Path, relativePath);
return Task.FromResult<Stream>(global::System.IO.File.OpenWrite(newPath));
#else
throw new PlatformNotSupportedException();
#endif
}
}