private async void Email_Unfocused(object sender, FocusEventArgs e)
{
Entry email = (Entry)FindByName("email");
bool result = await model.CheckEmail(email.Text);
if (result)
{
email.TextColor = Color.Red;
await Application.Current.MainPage.DisplayAlert("Greška", "Email već postoji !", "OK");
}
else
{
email.TextColor = Color.Black;
}
}