iot/projects/XamarinApp/XamarinApp/MainPage.xaml.cs

using System;
using System.ComponentModel;
using System.Threading.Tasks;
using Xamarin.Forms;

namespace XamarinApp
{
    [DesignTimeVisible(false)]
    public partial class MainPage : ContentPage
    {
        private const string baseUrlKey = "baseUrl";
        private string _baseUrl;

        public MainPage()
        {
            InitializeComponent();
            this.option.Source = ImageSource.FromResource($"{this.GetType().Assembly.GetName().Name}.Images.options.png");
            if (!Application.Current.Properties.ContainsKey(baseUrlKey))
            {
                Application.Current.Properties[baseUrlKey] = "http://49.4.92.112";
            }
            this._baseUrl = Application.Current.Properties[baseUrlKey] as string;
            this.webView.Source = this._baseUrl;
            this.Appearing += MainPage_Appearing;
        }

        private async void MainPage_Appearing(object sender, EventArgs e)
        {
            if (string.IsNullOrEmpty(this._baseUrl))
            {
                await SetBaseUrl();
            }
            else
            {
                this.webView.Source = this._baseUrl;
            }
        }

        private async void ImageButton_Clicked(object sender, EventArgs e)
        {
            await SetBaseUrl();
        }

        private async Task SetBaseUrl()
        {
            var input = await DisplayPromptAsync("服务器", "配置服务器地址", "确定", "取消", this._baseUrl, keyboard: Keyboard.Url, initialValue: this._baseUrl);
            if (!string.IsNullOrEmpty(input))
            {
                Application.Current.Properties[baseUrlKey] = input;
                this._baseUrl = input;
                this.webView.Source = this._baseUrl;
            }
        }
    }
}