电子邮件验证得到 System.ArgumentNullException：'值不能为空

Question

当输入框为空且我按下按钮时。我收到此错误消息 System.ArgumentNullException：'Value cannot be null. Parameter name: input' 我尝试了很多方法来弄清楚

        public MainPage()
    {
        InitializeComponent();
    }
    protected override async void OnAppearing()
    {
        base.OnAppearing();
        listmembers.ItemsSource = await App.Database.GetMemberAsync();
    }

    private async void Button_Clicked(object sender, EventArgs e)
    {

        var email = loginEmail.Text;
        var emailpattern = @"^([\w\.\-]+)@([\w\-]+)((\.(\w){2,3})+)$";


        if (Regex.IsMatch(email, emailpattern))
        {
            await App.Database.SaveMemberAsync(new Member
            {
                Name = loginEmail.Text,
            });
            loginEmail.Text =  string.Empty;
            listmembers.ItemsSource = await 
                App.Database.GetMemberAsync();
        }

        else
        {
            await DisplayAlert("Error", "Invaild Email", "ok");
        }
    }
}

Answer 1

您需要测试 null

if (!string.IsNullOrEmpty(email) && Regex.IsMatch(email, emailpattern))

电子邮件验证得到 System.ArgumentNullException：'值不能为空

Email validation getting System.ArgumentNullException: 'Value cannot be null

c#

xamarin.forms