Xamarin 选择器未显示列表中的日期 [英] Xamarin picker not showing the date from the list

问题描述

我有以下代码:

 <local:PisterosViewModel/></ContentPage.BindingContext><Picker x:Name="pck_Pisteros";ItemDisplayBinding="{Binding PisteroN}";ItemsSource="{Binding PisterosLista}";SelectedItem="{Binding PisterosLista}";标题=Seleccione el usuario..."/>

然后是我的模型:

使用系统；使用 System.Collections.Generic;使用 System.Collections.ObjectModel;使用 System.Diagnostics.Contracts;使用 System.Text;命名空间 ServLottery.Models{公开课 Pisteros{公共字符串 PisteroID { 获取；放;}公共字符串 PisteroN { 获取；放;}}}

和视图模型:

使用系统；使用 System.Collections.Generic;使用 System.Collections.ObjectModel;使用 System.Text;命名空间 ServLottery.Models{公共类 PisterosViewModel{公共 IList<Pisteros>PisterosLista { 得到;放;}公共 PisterosViewModel(){尝试{PisterosLista = new ObservableCollection<Pisteros>();GetPisteros();}捕获(异常前){扔前;}}私有异步 void GetPisteros(){尝试{RestClient 客户端 = new RestClient();var pist = await client.Get(https://servicentroapi.azurewebsites.net/api/Pisteros");if (pist != null){PisterosLista = pist;}}捕获(异常前){扔前;}}}}

我在 var pist 中设置了一个断点，它确实有值，然后 Pisteros 列表似乎也获得了值，并且在页面加载时执行，所以我不明白是什么问题，但选择器从来没有显示选项.

解决方案

欢迎来到 SO！

似乎Xaml中的BindingContext无法处理动态数据，例如来自Web服务器的API数据.

在 ContentPage 中使用编码动态绑定 ItemSource 有一个解决方法，也可以参考

I have the following code:

    <ContentPage.BindingContext>
        <local:PisterosViewModel/>
    </ContentPage.BindingContext>

<Picker x:Name="pck_Pisteros"
                        ItemDisplayBinding="{Binding PisteroN}"
                        ItemsSource="{Binding PisterosLista}"
                        SelectedItem="{Binding PisterosLista}"
                        Title="Seleccione el usuario..."/>

Then my Model:

using System;
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.Diagnostics.Contracts;
using System.Text;

namespace ServLottery.Models
{
    public class Pisteros
    {
        public string PisteroID { get; set; }
        public string PisteroN { get; set; }

    }

}

and the view model:

using System;
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.Text;

namespace ServLottery.Models
{
    public class PisterosViewModel
    {
        public IList<Pisteros> PisterosLista { get; set; }

        public PisterosViewModel()
        {
            try
            {
                PisterosLista = new ObservableCollection<Pisteros>();
                GetPisteros();
            }
            catch (Exception ex)
            {
                throw ex;
            }
        }

        private async void GetPisteros()
        {
            try
            {
                RestClient client = new RestClient();
                var pist = await client.Get<Models.Pisteros>("https://servicentroapi.azurewebsites.net/api/Pisteros");
                if (pist != null)
                {
                    PisterosLista = pist;
                }
            }
            catch (Exception ex)
            {
                throw ex;
            }

        }

    }
}

I set an breakpoint in var pist and it does have the values, then Pisteros list seems to get the values too, and this is executed when the page load, so I don't understand what's the problem, but the picker never shows the options.

解决方案

Welcome to SO !

It seems like BindingContext in Xaml can not deal with the dynamical data ,such API data from web server .

There is a workaround binding ItemSource dynamically by using coding in ContentPage , also can refer to this officail sample .

Therefore , adding code in Page.Xaml.cs as follow :

protected override async void OnAppearing()
{
    pck_Pisteros.ItemsSource = await GetTasksAsync();
    base.OnAppearing();
}

private async Task<List<Pisteros>> GetTasksAsync()
{
    List<Pisteros> PisterosLista = new List<Pisteros>();
    HttpClient client = new HttpClient();
    Uri uri = new Uri(string.Format("https://servicentroapi.azurewebsites.net/api/Pisteros", string.Empty));
    HttpResponseMessage response = await client.GetAsync(uri);
    if (response.IsSuccessStatusCode)
    {
        string content = await response.Content.ReadAsStringAsync();
        PisterosLista = JsonConvert.DeserializeObject<List<Pisteros>>(content);
        Console.WriteLine("content :: " + content);
        Console.WriteLine("Data :: " + PisterosLista);
    }

    return PisterosLista;
}

Now it will show:

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