Xamrin.Forms尝试使用Firebase实时数据库创建电子邮件检查

根据您的描述，您想要创建项目，使用电子邮件帐户注册帐户，并注册以浏览另一个内容页面。

但是我发现您的代码有点混乱，我做了一个简单的示例，您可以看一下：

 <StackLayout>
    <!--  Place new controls here  -->
    <Entry x:Name="txtemail" Placeholder="Email" />
    <Entry x:Name="txtpassword" Placeholder="Enter Password" />
    <Entry x:Name="txtstudentId" Placeholder="Enter Student Id" />
    <StackLayout HorizontalOptions="CenterAndExpand" Orientation="Horizontal">
        <Button
            x:Name="btnSign"
            Clicked="BtnSign_Clicked"
            Text="Sign up"
            WidthRequest="200" />
        <Button
            x:Name="btnRegister"
            Clicked="BtnRegister_Clicked"
            Text="Retrive"
            WidthRequest="200" />
    </StackLayout>
</StackLayout>

 public partial class MainPage : ContentPage
{
    FirebaseHelper firebaseHelper = new FirebaseHelper();
    public MainPage()
    {
        InitializeComponent();
    }

    private async void BtnSign_Clicked(object sender, EventArgs e)
    {
        var person = await firebaseHelper.GetPerson(txtemail.Text);
        if (person != null)
        {
            if(person.Email==txtpassword.Text)
            {
                await Navigation.PushAsync(new Page1());
            }
            else
            {
                await DisplayAlert("Fail", "Password is not correct!", "OK");
            }              
        }
        else
        {
            await DisplayAlert("Fail", "No email Available!", "OK");
        }
    }

    private async void BtnRegister_Clicked(object sender, EventArgs e)
    {
        if(await RegisterAccount())
        {
            await firebaseHelper.AddPerson(txtemail.Text, txtpassword.Text, txtstudentId.Text);
            txtemail.Text = string.Empty;
            txtpassword.Text = string.Empty;
            txtstudentId.Text = string.Empty;
            await DisplayAlert("Success", "Person Added Successfully", "OK");
        }
        else
        {
            await DisplayAlert("Fail", "Person Added Fail", "OK");
        }


    }

    private async Task<bool> RegisterAccount()
    {
        var hasSymbols = new Regex(@"[!@#$%^&*()_+=\[{\]};:<>|./?,-]");

        //null or empty field validation, check weather email and password is null or empty
        if (string.IsNullOrEmpty(txtemail.Text) || string.IsNullOrEmpty(txtpassword.Text))
        {
          await  DisplayAlert("Empty Values", "Please enter Email and Password", "OK");

            return false;
        }
        else if (!txtemail.Text.Contains("@"))
        {
            await DisplayAlert("", "Email Address is Invalid", "OK");
            return false;
        }
        else if (txtpassword.Text.Length < 8)
        {
            await DisplayAlert("", "Password is less than 8 characters", "OK");
            return false;
        }
        else if (!txtpassword.Text.Any(char.IsUpper))
        {
            await DisplayAlert("", "Password Must Contain at Least 1 Uppcase Letter", "OK");
            return false;
        }
        else if (!hasSymbols.IsMatch(txtpassword.Text))
        {
            await DisplayAlert("", "Password should contain At least one special case characters", "OK");
            return false;
        }

        else if (string.IsNullOrEmpty(txtstudentId.Text))
        {
            await DisplayAlert("Empty Values", "Please enter Student ID", "OK");
            return false;
        }

        else
        {
            var person = await firebaseHelper.GetPerson(txtemail.Text);
            if (person != null)
            {
                await DisplayAlert("fail", "Email already exist", "OK");
                return false;

            }
        }

        return true;

    }
}

public class Register
{
    public string Email { get; set; }
    public string Password { get; set; }
    public string StudentId { get; set; }
}

 public class FirebaseHelper
{
    FirebaseClient firebase = new FirebaseClient("https://testapp1-ebb27-6e5ba.firebaseio.com/");

    public async Task<List<Register>> GetAllPersons()
    {

        return (await firebase
          .Child("Persons")
          .OnceAsync<Register>()).Select(item => new Register
          {
              Email = item.Object.Email,
              Password = item.Object.Password,
              StudentId=item.Object.StudentId

          }).ToList();
    }

    public async Task AddPerson(string email, string password, string studentid)
    {

        await firebase
          .Child("Persons")
          .PostAsync(new Register() { Email = email, Password = password, StudentId = studentid });

    }

    public async Task<Register> GetPerson(string email)
    {
        var allPersons = await GetAllPersons();
        await firebase
          .Child("Persons")
          .OnceAsync<Register>();
        return allPersons.Where(a => a.Email == email).FirstOrDefault();
    }


}

这是我在github上的示例：

https://github.com/CherryBu/RegisterApp