Question

在我的应用程序中，我已连接Firebase并尝试填充列表视图，但是一开始，我没有看到任何记录。它只是显示一个空白页，列表视图中没有任何内容。

这是我的firebasehelper.cs

{
class FirebaseHelper
{
    FirebaseClient firebase = new FirebaseClient("https://mylimo-b2029.firebaseio.com/");


    public async Task<List<users>> GetAllUsers()
    {

        try
        {
          return (await firebase
         .Child("Users")
         .OnceAsync<users>()).Select(item => new users
         {
             //,

             first_name = item.Object.first_name,
             last_name = item.Object.last_name,
             password = item.Object.password,
             user_id = item.Object.user_id,
         }).ToList();
        }
        catch (Exception ex)
        {
            throw new Exception("GetUsers  Additional information..." + ex, ex);
        }
    }    


    public async Task<users> GetUsers(string usr_id)
    {
        try
        {
            var allUsers = await GetAllUsers();
            await firebase
              .Child("users")
              .OnceAsync<users>();
            return allUsers.Where(a => a.user_id == usr_id).FirstOrDefault();
        }


        catch (Exception ex)
        {
            throw new Exception("GetUsers  Additional information..." + ex, ex);
        }
    }
}

下面是MainPage.xaml.cs

 public partial class MainPage : ContentPage
{
    FirebaseHelper firebaseHelper = new FirebaseHelper();
    public MainPage()
    {
        try
        {
            InitializeComponent();
        }
        catch (Exception ex)
        {
            throw new Exception("InitializeComponent  Additional information..." + ex, ex);
        }
    }

    protected async override void OnAppearing()
    {
        try
        {
            base.OnAppearing();
            var allUsers = await firebaseHelper.GetAllUsers();
            lstPersons.ItemsSource = allUsers;
        }

        catch (Exception ex)
        {
            throw new Exception("OnAppearing  Additional information..." + ex, ex);
        }




    }

在应用程序启动时，它将仅显示一个空白列表视图控件，没有任何记录，

。

我的firebase数据库如下] 1

Answer 1

您编写的代码是正常的。但是您可以减少一些步骤。

请参考以下使用Firebase数据库的方法。

首先，请打开firebase数据库控制台，将读/写身份验证规则设置为null，如以下屏幕截图所示。

然后创建一个模块user。

public class User
{
    public string first_name { get; set; }
    public string last_name { get; set; }

    public string password { get; set; }

    public int userid { get; set; }
}

有我的firebasehelper。

   public class Firebasehelper
{
    FirebaseClient firebase;
    public Firebasehelper()
    {
        firebase = new FirebaseClient("https://fir-databasedemo-62a72.firebaseio.com/");

    }

    public async Task AddUser(int userid, string first_name, string last_name, string password)
    {

        await firebase
          .Child("Users")
          .PostAsync(new User() { userid = userid, first_name = first_name, last_name= last_name, password= password });
    }
    public async Task<List<User>> GetAllUsers()
    {

        return (await firebase
          .Child("Users")
          .OnceAsync<User>()).Select(item => new User
          {

              userid = item.Object.userid,
              first_name = item.Object.first_name,
              last_name = item.Object.last_name,
              password = item.Object.password
          }).ToList();
    }
}

请不要直接在Firebase中创建记录。我们应该按代码添加这些记录。成功添加这些记录后，您可以在firebase控制台中查看这些记录。

与以下代码一起使用。

  private async void BtnAdd_Clicked(object sender, EventArgs e)
    {
        // AddUser(int userid, string first_name, string last_name, string password)
        await firebaseHelper.AddUser(Convert.ToInt32(1), "Jon","hard","123.com");
        await firebaseHelper.AddUser(Convert.ToInt32(1), "Leon", "esay", "1234.com");
        await firebaseHelper.AddUser(Convert.ToInt32(1), "Rebecca", "middlue", "12345.com");
        await DisplayAlert("Success", "Person Added Successfully", "OK");
       var allPersons = await firebaseHelper.GetAllUsers();
       lstPersons.ItemsSource = allPersons;
    }

有我的MainPage.xaml。

 <ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
         xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
         xmlns:local="clr-namespace:RetireveRecordDemo"
         x:Class="RetireveRecordDemo.MainPage">
  <StackLayout>
    <Button x:Name="BtnAdd" Text="add" />

    <ListView x:Name="lstPersons">
        <ListView.ItemTemplate>
            <DataTemplate>
                <ViewCell>
                    <StackLayout>

                        <Label Text="{Binding first_name}"  > 
                 </Label>
                        <Label Text="{Binding last_name}" > 
                 </Label>

                    </StackLayout>
                </ViewCell>
            </DataTemplate>
        </ListView.ItemTemplate>
    </ListView>
</StackLayout>
</ContentPage>

MainPage.xml.cs

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

        BtnAdd.Clicked += BtnAdd_Clicked;
    }

    private async void BtnAdd_Clicked(object sender, EventArgs e)
    {
        // AddUser(int userid, string first_name, string last_name, string password)
        await firebaseHelper.AddUser(Convert.ToInt32(1), "Jon","hard","123.com");
        await firebaseHelper.AddUser(Convert.ToInt32(1), "Leon", "esay", "1234.com");
        await firebaseHelper.AddUser(Convert.ToInt32(1), "Rebecca", "middlue", "12345.com");
        await DisplayAlert("Success", "Person Added Successfully", "OK");
       var allPersons = await firebaseHelper.GetAllUsers();
       lstPersons.ItemsSource = allPersons;
    }

    protected async override void OnAppearing()
    {

        base.OnAppearing();


        try
        {
            base.OnAppearing();
            var allUsers = await firebaseHelper.GetAllUsers();
            lstPersons.ItemsSource = allUsers;
        }

        catch (Exception ex)
        {
            throw new Exception("OnAppearing  Additional information..." + ex, ex);
        }
    }
}

有正在运行的屏幕截图。

有我的演示。 https://github.com/851265601/RetireveRecordDemo

在Firebase数据库中有一篇关于CRUD的有用文章。 https://www.c-sharpcorner.com/article/xamarin-forms-working-with-firebase-realtime-database-crud-operations/

无法在Xamarin C＃中从Firebase检索记录

1 个答案: