如何使用 xamarain 表单实时显示 firebase 的选取器项目并在选择项目时添加到 firebase

Question

我想显示 firebase 中的选择器项目，如何做到这一点？

<Picker x:Name="AppointmentPatientName" Title="Patient Name" >
            <Picker.Items>
                <x:String>Ahmad</x:String>
                <x:String>Ali</x:String>
                <x:String>Omar</x:String>
                <x:String>Alma</x:String>
                <x:String>Aya</x:String>
                <x:String>Ammar</x:String>
                <x:String>Noor</x:String>
            </Picker.Items>
        </Picker>
      

Answer 1

1. 当您想使用xamarin表单实时显示firebase的Picker项时，请先从firebase获取项，然后将项绑定到picker。

   型号：

   公共类 Person
   {
    公共 int PersonId { 获取；放; }
    公共字符串名称{获取;放; }
   }
   

   获取、添加、删除 Firebase 实时数据库的项目：

   公共类FirebaseHelper
    {
    FirebaseClient firebase = new FirebaseClient("https://fir-xxxxx-default-rtdb.firebaseio.com/");// 您可以从自己的 Firebase 数据库获取的链接。 https://console.firebase.google.com/
   
    公共异步任务<列表<人员>>获取所有人员()
    {
   
        返回（等待 firebase
          .Child(“人”)
          .OnceAsync()).Select(item => 新 Person
          {
              名称 = 项目.对象.名称,
              PersonId = 项目.Object.PersonId
          }).ToList();
    }
   
    公共异步任务AddPerson（int personId，字符串名称）
    {
   
        等待火力基地
          .Child(“人”)
          .PostAsync(new Person() { PersonId = personId, Name = 姓名 });
    }
   
    公共异步任务; GetPerson（int personId）
    {
        var allPersons = 等待 GetAllPersons();
        等待火力基地
          .Child(“人”)
          .OnceAsync();
        return allPersons.Where(a => a.PersonId == personId).FirstOrDefault();
    }
   
    公共异步任务UpdatePerson（int personId，字符串名称）
    {
        var toUpdatePerson =（等待 firebase
          .Child(“人”)
          .OnceAsync()).Where(a => a.Object.PersonId == personId).FirstOrDefault();
   
        等待火力基地
          .Child(“人”)
          .Child(toUpdatePerson.Key)
          .PutAsync(new Person() { PersonId = personId, Name = 姓名 });
    }
   
    公共异步任务DeletePerson(int personId)
    {
        var toDeletePerson =（等待 firebase
          .Child(“人”)
          .OnceAsync()).Where(a => a.Object.PersonId == personId).FirstOrDefault();
        等待 firebase.Child("Persons").Child(toDeletePerson.Key).DeleteAsync();
   
    }
   }
   

   绑定选择器：

2. 当您选择项目时想要将项目添加到 Firebase 时，请先获取所选项目，然后添加它。

   使用SelectedIndexChanged事件获取所选项目。然后调用 FirebaseHelper 的 Add 方法。

   void OnPickerSelectedIndexChanged（对象发送者，EventArgs e）
   {
    var picker = (Picker)发送者;
    int selectedIndex = picker.SelectedIndex;
   
    if (selectedIndex != -1)
    {
        selectedItem = (string)picker.ItemsSource[selectedIndex];
    }
   }
   

Answer 2

         MainPage.xaml 



            <Entry x:Name="TxtName" 
                   Placeholder="Name (Required)"/>
            
            <DatePicker x:Name="date"/>
            <Picker Title="Select a state"
                    x:Name="state"
                    TitleColor="Red">
                <Picker.Items>
                    <x:String>kerala</x:String>
                    <x:String>Pujab</x:String>
                </Picker.Items>
            </Picker>
            <StackLayout  HorizontalOptions="CenterAndExpand" Orientation="Horizontal">
                <Button x:Name="BtnAdd" WidthRequest="200" Text="Add" Clicked="BtnAdd_Clicked"/>
                <Button x:Name="BtnDelete" WidthRequest="200" Text="Delete" Clicked="BtnDelete_Clicked" />
            </StackLayout>

            <StackLayout HorizontalOptions="CenterAndExpand" Orientation="Horizontal">
                <Button x:Name="BtnUpdate" WidthRequest="200" Text="Update" Clicked="BtnUpdate_Clicked" />
            </StackLayout>

            <ListView x:Name="LstPersons" ItemSelected="LstPersons_OnItemSelected">
                <ListView.ItemTemplate>
                    <DataTemplate>
                        <TextCell Text="{Binding Name}"></TextCell>
                    </DataTemplate>
                </ListView.ItemTemplate>
            </ListView>

     

mainpage.xaml.cs

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

    public MainPage()
    {
        InitializeComponent();
    }


    protected override async void OnAppearing()
    {
        base.OnAppearing();

        await FetchAllPersons();
    }

    private async void BtnAdd_Clicked(object sender, EventArgs e)
    {
        if (!IsFormValid())
        {
            await DisplayAlert("Error", "All are required fields", "OK");
            return;
        }

        Person person = await firebaseHelper.GetPerson(TxtName.Text);

        if (person != null)
        {
            await DisplayAlert("Error", "A person with that name already exist", "OK");
            return;
        }

        await firebaseHelper.AddPerson(TxtName.Text,date.Date, (string)state.SelectedItem);

        TxtName.Text = string.Empty;           
        date.Date = DateTime.Now;
        state.SelectedItem = string.Empty;
       
        await DisplayAlert("Success", "Person Added Successfully", "OK");

        await FetchAllPersons();
    }

    private async void BtnUpdate_Clicked(object sender, EventArgs e)
    {
        if (SelectedPerson == null)
        {
            await DisplayAlert("Error", "A person must be selected to proceed", "OK");
            return;
        }
        
        if (!IsFormValid())
        {
            await DisplayAlert("Error", "All are required fields", "OK");
            return;
        }

        Person person = await firebaseHelper.GetPerson(TxtName.Text);

        if (person != null && person.PersonId != SelectedPerson.PersonId)
        {
            await DisplayAlert("Error", "A person with that name already exist", "OK");
            return;
        }

        await firebaseHelper.UpdatePerson(SelectedPerson.PersonId, TxtName.Text, date.Date, (string)state.SelectedItem);

        TxtName.Text = string.Empty;           
        date.Date = DateTime.Now;
        state.SelectedItem = string.Empty;
        await DisplayAlert("Success", "Person Updated Successfully", "OK");

        await FetchAllPersons();
    }

    private async void BtnDelete_Clicked(object sender, EventArgs e)
    {
        if (SelectedPerson == null)
        {
            await DisplayAlert("Error", "A person must be selected to proceed", "OK");
            return;
        }

        await firebaseHelper.DeletePerson(SelectedPerson.PersonId);

        await DisplayAlert("Success", "Person Deleted Successfully", "OK");

        await FetchAllPersons();
    }

    private async void LstPersons_OnItemSelected(object sender, SelectedItemChangedEventArgs e)
    {
        var person = await firebaseHelper.GetPerson(SelectedPerson.PersonId);

        TxtName.Text = person.Name;           
        date.Date = person.Date;
        state.SelectedItem = person.State;
    }

    private async Task FetchAllPersons()
    {
        var allPersons = await firebaseHelper.GetAllPersons();

        LstPersons.ItemsSource = allPersons;
    }

    private Person SelectedPerson => (Person)LstPersons.SelectedItem;

    private bool IsFormValid() => IsNameValid();

    private bool IsNameValid() => !string.IsNullOrWhiteSpace(TxtName.Text);
                  
}

person.cs

public class Person
{
   
    public Guid PersonId { get; set; }
    public string Name { get; set; }      
    public DateTime Date { get; set; }
    public string State { get; set; }
}

firbasehelper.cs

public class FirebaseHelper

{
    
private readonly string ChildName = "Persons";

    readonly FirebaseClient firebase = new FirebaseClient("https://XXXXXXyour__db_urlXXXXX/");

    public async Task<List<Person>> GetAllPersons()
    {
        return (await firebase
            .Child(ChildName)
            .OnceAsync<Person>()).Select(item => new Person
            {
                PersonId = item.Object.PersonId,
                Name = item.Object.Name,                    
                Date = item.Object.Date,
                State = item.Object.State
            }).ToList();
    }

    public async Task AddPerson(string name,DateTime date, string state)
    {
        await firebase
            .Child(ChildName)
            .PostAsync(new Person() { PersonId = Guid.NewGuid(), Name = name, Date = date,State=state });
    }

    public async Task<Person> GetPerson(Guid personId)
    {
        var allPersons = await GetAllPersons();
        await firebase
            .Child(ChildName)
            .OnceAsync<Person>();
        return allPersons.FirstOrDefault(a => a.PersonId == personId);
    }

    public async Task<Person> GetPerson(string name)
    {
        var allPersons = await GetAllPersons();
        await firebase
            .Child(ChildName)
            .OnceAsync<Person>();
        return allPersons.FirstOrDefault(a => a.Name== name);
    }

    public async Task UpdatePerson(Guid personId, string name,DateTime date, string state)
    {
        var toUpdatePerson = (await firebase
            .Child(ChildName)
            .OnceAsync<Person>()).FirstOrDefault(a => a.Object.PersonId == personId);

        await firebase
            .Child(ChildName)
            .Child(toUpdatePerson.Key)
            .PutAsync(new Person() { PersonId = personId, Name = name,Date = date, State = state });
    }

    public async Task DeletePerson(Guid personId)
    {
        var toDeletePerson = (await firebase
            .Child(ChildName)
            .OnceAsync<Person>()).FirstOrDefault(a => a.Object.PersonId == personId);
        await firebase.Child(ChildName).Child(toDeletePerson.Key).DeleteAsync();
    }
}