Question

我在绑定我的Xamarin Picker方面遇到了一些困难，所以当我更改所选项目时，它会触发我表单中的刷新。我正在使用XAML代码隐藏。

这是XAML。您可以看到Picker已定义。数据被很好地绑定，它正在从我的List中加载Name属性。

上面有一个Id“Entry”字段，这是无效的部分。我想要做的是当选择器被“挑选”时，从列表/选择列表项中显示Id字段。

我在网上找到的一些示例代码也可以使用 - Surname和Forename在输入数据时都会更新相应的标签。所以它必须与picker和SelectedItem绑定或我尝试使用OnPropertyChanged的方式有关。

<ContentPage xmlns="http://xamarin.com/schemas/2014/forms" xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml" x:Class="TechsportiseApp.MainUI.Races">
  <StackLayout Padding="0,20,0,0">
    <Label Text="Race ID" />
    <Entry Text="{Binding Id}" />
    <Picker ItemsSource="{Binding RaceList}" ItemDisplayBinding="{Binding Name}" SelectedItem="{Binding RacesIndex, Mode=TwoWay}" />
    <Label Text="Data Binding 101 Demo" FontAttributes="Bold" HorizontalOptions="Center" />
    <Label Text="Forename:" />
    <Entry Text="{Binding Forename, Mode=TwoWay}" />
    <Label Text="Surname:" />
    <Entry Text="{Binding Surname, Mode=TwoWay}" />
    <Label Text="Your forename is:" />
    <Label Text="{Binding Forename}" />
    <Label Text="Your surname is:" />
    <Label Text="{Binding Surname}" />
  </StackLayout>
</ContentPage>

我正在使用的ViewModel如下所示。

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Threading.Tasks;
using Newtonsoft.Json;
using RestSharp;
using TechsportiseApp.API.Models;
using Xamarin.Forms;
using TechsportiseApp.API;

namespace TechsportiseApp.MainUI.Models
{
public class RacesViewModel : INotifyPropertyChanged
{
    int _id;
    public int Id
    {
        get
        {
            return _id;
        }
        set
        {
            if (_id != value)
            {
                _id = value;
                OnPropertyChanged("Id");
            }
        }
    }
    string _name;
    public string Name
    {
        get
        {
            return _name;
        }
        set
        {
            if (_name != value)
            {
                _name = value;
                OnPropertyChanged("Name");
            }
        }
    }

    public List<Race> RaceList
    {
        get
        {
            var racelist = RacesAPI.GetRaces();
            return racelist;
        }
    }

    int _racesIndex;
    public int RacesIndex
    {
        get
        {
            return _racesIndex;
        }
        set
        {
            if (_racesIndex != value)
            {
                _racesIndex = value;

                // trigger some action to take such as updating other labels or fields
                OnPropertyChanged("RacesIndex");
            }
        }
    }

    string forename, surname;

    public string Forename
    {
        get
        {
            return forename;
        }
        set
        {
            if (forename != value)
            {
                forename = value;
                OnPropertyChanged("Forename");
            }
        }
    }

    public string Surname
    {
        get
        {
            return surname;
        }
        set
        {
            if (surname != value)
            {
                surname = value;
                OnPropertyChanged("Surname");
            }
        }
    }

    public event PropertyChangedEventHandler PropertyChanged;

    protected virtual void OnPropertyChanged(string propertyName)
    {
        var changed = PropertyChanged;
        if (changed != null)
            {
                PropertyChanged(this, new PropertyChangedEventArgs(propertyName));               
            }
    }       
 }

如果需要，这里是我用来填充列表数据的代码，我从API的JSON响应中获取。

using Newtonsoft.Json;
using RestSharp;
using System;
using System.Collections.Generic;
using System.Text;
using TechsportiseApp.API.Models;
using TechsportiseApp.MainUI;
using Xamarin.Forms;

namespace TechsportiseApp.API
{
    public class RacesAPI
    {
        public static List<Race> GetRaces()
        {
            var raceList = new List<Race>();
            string APIServer = Application.Current.Properties["APIServer"].ToString();
            string Token = Application.Current.Properties["Token"].ToString();
            var client = new RestClient(APIServer);
            var request = new RestRequest("api/race", Method.GET);
            request.AddHeader("Content-type", "application/json");
            request.AddHeader("Authorization", "Bearer " + Token);
            var response = client.Execute(request) as RestResponse;
            raceList = JsonConvert.DeserializeObject<List<Race>>(response.Content);
            return raceList;
        }
    }
}

有什么想法吗？我一直试图破解这几天，但似乎无法让它发挥作用。

Answer 1

从我所看到的，你决不设置Id的值。可能你想把它放在RacesIndex的setter中。 RacesIndex也应绑定到SelectedIndex，而不是SelectedItem。我假设Race类有一个Id属性，它是一个int，所以请看下面的内容。如果要绑定到selectedItem，则绑定到的属性应与列表中的属性相同

 int _racesIndex;
public int RacesIndex
{
    get
    {
        return _racesIndex;
    }
    set
    {
        if (_racesIndex != value)
        {
            _racesIndex = value;

            // trigger some action to take such as updating other labels or fields
            Id = racelist[value].RaceId;
            OnPropertyChanged("RacesIndex");
        }
    }
}

绑定到XAML中的Xamarin Picker SelectedItem而不是重新加载表单

1 个答案: