如何从选定的选取器更新 Label 元素？ （Xamarin 形式）

Question

我目前正在开展一个向您显示实时股票价格的项目。 我想使用选择器系统获取任何符号的价格，该系统通过将所选项目添加到下载字符串请求的链接中来显示选择器中所选项目的价格。 我遇到的问题是，当我更改选择器时，什么也没有发生。

C# 代码：

using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Net;

using Xamarin.Forms;
using Xamarin.Forms.Xaml;

namespace Stock_WatchList
{
    [XamlCompilation(XamlCompilationOptions.Compile)]
    public partial class sybmolSelector : ContentPage
    {
        public string price { get; set; }
        public sybmolSelector()
        {
            InitializeComponent();

            BindingContext = this;
        }

        private void SymbolSelector_SelectedIndexChanged(object sender, EventArgs e)
        {
            Picker picker = sender as Picker;
            var selectedItem = picker.SelectedItem;

            var link = "https://sandbox.iexapis.com/stable/stock/" + selectedItem + "/price?token=Tsk_57bebc1d051340dbaad8656ab0027e90";

            var client1 = new WebClient();
            string a = client1.DownloadString(link);
            price = "$" + a;
        }
    }
}

这是 Xamarin.Forms 代码：

<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
             x:Class="Stock_WatchList.sybmolSelector"
             BackgroundColor="Black"
             NavigationPage.IconColor="LimeGreen">
    <ContentPage.Content>
        <StackLayout>
            <Label TextColor="LimeGreen" BackgroundColor="Black" Text="----------------------- Select A Symbol -------------------------" FontSize="19" LineBreakMode="TailTruncation"></Label>
            <Picker x:Name="Picker" SelectedIndexChanged="SymbolSelector_SelectedIndexChanged" TextColor="LimeGreen" BackgroundColor="#111111">
                <Picker.Items>
                    <x:String>AAPL</x:String>
                    <x:String>NIO</x:String>
                    <x:String>AAPL</x:String>
                    <x:String>NIO</x:String>
                    <x:String>AAPL</x:String>
                    <x:String>NIO</x:String>
                    <x:String>AAPL</x:String>
                    <x:String>NIO</x:String>
                    <x:String>AAPL</x:String>
                    <x:String>NIO</x:String>
                    <x:String>AAPL</x:String>
                    <x:String>NIO</x:String>
                    <x:String>AAPL</x:String>
                    <x:String>NIO</x:String>
                    <x:String>AAPL</x:String>
                    <x:String>NIO</x:String>
                </Picker.Items>
            </Picker>
            <Label Margin="5" Text="{Binding selectedItem}" HorizontalOptions="Start" TextColor="White" FontSize="40"/>
            <Label Margin="5,0,5,5" Text="{Binding price}" HorizontalOptions="Start" TextColor="White" FontSize="50"/>
        </StackLayout>
    </ContentPage.Content>
</ContentPage>

在此先感谢，内森 T。

Answer 1

为您的 label 命名：

<Label x:Name="lblPicker" TextColor="LimeGreen" BackgroundColor="Black" Text="----------------------- Select A Symbol -------------------------" FontSize="19" LineBreakMode="TailTruncation"></Label>

然后，您可以在后面的代码中访问此 label 并将选择器值分配给 label：

private void SymbolSelector_SelectedIndexChanged(object sender, EventArgs e)
        {
            Picker picker = sender as Picker;
            var selectedItem = picker.SelectedItem;

            var link = "https://sandbox.iexapis.com/stable/stock/" + selectedItem + "/price?token=Tsk_57bebc1d051340dbaad8656ab0027e90";

            var client1 = new WebClient();
            string a = client1.DownloadString(link);
            lblPicker.Text = "$" + a;
        }

您也可以在 viewmodel 中执行此操作，但为此您需要将选择器的 ItemSource 属性与 ViewModel 的属性绑定，但在此之前您可以通过这种方式获取代码