i have a button and an image view when i take image form gallery how can i save it ?

async void Button_Clicked(object sender, EventArgs e)
{
await CrossMedia.Current.Initialize();
if (!CrossMedia.Current.IsPickPhotoSupported)
{
await DisplayAlert("error", "errore", "ok");
return;
}
var mediaoption = new PickMediaOptions()
{
PhotoSize = PhotoSize.Medium
};
var selectedimagefile = await CrossMedia.Current.PickPhotoAsync(mediaoption);
if (selectedimagefile == null)
{
await DisplayAlert("error", "try agisn", "ok");
return;
}
Selectedimage.Source = ImageSource.FromStream(()=> selectedimagefile.GetStream())
}