添加xamarinFormApp例子,安卓,iOS,WPF

Examples/xamarinFormApp/xamarinFormApp/ViewModels/AboutViewModel.cs

@@ -0,0 +1,18 @@
+using System;
+using System.Windows.Input;
+using Xamarin.Essentials;
+using Xamarin.Forms;
+
+namespace xamarinFormApp.ViewModels
+{
+    public class AboutViewModel : BaseViewModel
+    {
+        public AboutViewModel()
+        {
+            Title = "About";
+            OpenWebCommand = new Command(async () => await Browser.OpenAsync("https://aka.ms/xamarin-quickstart"));
+        }
+
+        public ICommand OpenWebCommand { get; }
+    }
+}

Examples/xamarinFormApp/xamarinFormApp/ViewModels/BaseViewModel.cs

@@ -0,0 +1,56 @@
+using System;
+using System.Collections.Generic;
+using System.ComponentModel;
+using System.Runtime.CompilerServices;
+
+using Xamarin.Forms;
+
+using xamarinFormApp.Models;
+using xamarinFormApp.Services;
+
+namespace xamarinFormApp.ViewModels
+{
+    public class BaseViewModel : INotifyPropertyChanged
+    {
+        public IDataStore<Item> DataStore => DependencyService.Get<IDataStore<Item>>();
+
+        bool isBusy = false;
+        public bool IsBusy
+        {
+            get { return isBusy; }
+            set { SetProperty(ref isBusy, value); }
+        }
+
+        string title = string.Empty;
+        public string Title
+        {
+            get { return title; }
+            set { SetProperty(ref title, value); }
+        }
+
+        protected bool SetProperty<T>(ref T backingStore, T value,
+            [CallerMemberName] string propertyName = "",
+            Action onChanged = null)
+        {
+            if (EqualityComparer<T>.Default.Equals(backingStore, value))
+                return false;
+
+            backingStore = value;
+            onChanged?.Invoke();
+            OnPropertyChanged(propertyName);
+            return true;
+        }
+
+        #region INotifyPropertyChanged
+        public event PropertyChangedEventHandler PropertyChanged;
+        protected void OnPropertyChanged([CallerMemberName] string propertyName = "")
+        {
+            var changed = PropertyChanged;
+            if (changed == null)
+                return;
+
+            changed.Invoke(this, new PropertyChangedEventArgs(propertyName));
+        }
+        #endregion
+    }
+}

Examples/xamarinFormApp/xamarinFormApp/ViewModels/ItemDetailViewModel.cs

@@ -0,0 +1,57 @@
+using System;
+using System.Diagnostics;
+using System.Threading.Tasks;
+using Xamarin.Forms;
+using xamarinFormApp.Models;
+
+namespace xamarinFormApp.ViewModels
+{
+    [QueryProperty(nameof(ItemId), nameof(ItemId))]
+    public class ItemDetailViewModel : BaseViewModel
+    {
+        private string itemId;
+        private string text;
+        private string description;
+        public string Id { get; set; }
+
+        public string Text
+        {
+            get => text;
+            set => SetProperty(ref text, value);
+        }
+
+        public string Description
+        {
+            get => description;
+            set => SetProperty(ref description, value);
+        }
+
+        public string ItemId
+        {
+            get
+            {
+                return itemId;
+            }
+            set
+            {
+                itemId = value;
+                LoadItemId(value);
+            }
+        }
+
+        public async void LoadItemId(string itemId)
+        {
+            try
+            {
+                var item = await DataStore.GetItemAsync(itemId);
+                Id = item.Id;
+                Text = item.Text;
+                Description = item.Description;
+            }
+            catch (Exception)
+            {
+                Debug.WriteLine("Failed to Load Item");
+            }
+        }
+    }
+}

Examples/xamarinFormApp/xamarinFormApp/ViewModels/ItemsViewModel.cs

@@ -0,0 +1,86 @@
+using System;
+using System.Collections.ObjectModel;
+using System.Diagnostics;
+using System.Threading.Tasks;
+
+using Xamarin.Forms;
+
+using xamarinFormApp.Models;
+using xamarinFormApp.Views;
+
+namespace xamarinFormApp.ViewModels
+{
+    public class ItemsViewModel : BaseViewModel
+    {
+        private Item _selectedItem;
+
+        public ObservableCollection<Item> Items { get; }
+        public Command LoadItemsCommand { get; }
+        public Command AddItemCommand { get; }
+        public Command<Item> ItemTapped { get; }
+
+        public ItemsViewModel()
+        {
+            Title = "Browse";
+            Items = new ObservableCollection<Item>();
+            LoadItemsCommand = new Command(async () => await ExecuteLoadItemsCommand());
+
+            ItemTapped = new Command<Item>(OnItemSelected);
+
+            AddItemCommand = new Command(OnAddItem);
+        }
+
+        async Task ExecuteLoadItemsCommand()
+        {
+            IsBusy = true;
+
+            try
+            {
+                Items.Clear();
+                var items = await DataStore.GetItemsAsync(true);
+                foreach (var item in items)
+                {
+                    Items.Add(item);
+                }
+            }
+            catch (Exception ex)
+            {
+                Debug.WriteLine(ex);
+            }
+            finally
+            {
+                IsBusy = false;
+            }
+        }
+
+        public void OnAppearing()
+        {
+            IsBusy = true;
+            SelectedItem = null;
+        }
+
+        public Item SelectedItem
+        {
+            get => _selectedItem;
+            set
+            {
+                SetProperty(ref _selectedItem, value);
+                OnItemSelected(value);
+            }
+        }
+
+        private async void OnAddItem(object obj)
+        {
+            await Shell.Current.GoToAsync(nameof(NewItemPage));
+        }
+
+        async void OnItemSelected(Item item)
+        {
+            if (item == null)
+                return;
+
+            // This will push the ItemDetailPage onto the navigation stack
+            await Shell.Current.GoToAsync($"{nameof(ItemDetailPage)}?{nameof(ItemDetailViewModel.ItemId)}={item.Id}");
+        }
+    }
+}

Examples/xamarinFormApp/xamarinFormApp/ViewModels/LoginViewModel.cs

@@ -0,0 +1,24 @@
+using System;
+using System.Collections.Generic;
+using System.Text;
+using Xamarin.Forms;
+using xamarinFormApp.Views;
+
+namespace xamarinFormApp.ViewModels
+{
+    public class LoginViewModel : BaseViewModel
+    {
+        public Command LoginCommand { get; }
+
+        public LoginViewModel()
+        {
+            LoginCommand = new Command(OnLoginClicked);
+        }
+
+        private async void OnLoginClicked(object obj)
+        {
+            // Prefixing with `//` switches to a different navigation stack instead of pushing to the active one
+            await Shell.Current.GoToAsync($"//{nameof(AboutPage)}");
+        }
+    }
+}

Examples/xamarinFormApp/xamarinFormApp/ViewModels/NewItemViewModel.cs

@@ -0,0 +1,65 @@
+using System;
+using System.Collections.Generic;
+using System.Text;
+using System.Windows.Input;
+using Xamarin.Forms;
+using xamarinFormApp.Models;
+
+namespace xamarinFormApp.ViewModels
+{
+    public class NewItemViewModel : BaseViewModel
+    {
+        private string text;
+        private string description;
+
+        public NewItemViewModel()
+        {
+            SaveCommand = new Command(OnSave, ValidateSave);
+            CancelCommand = new Command(OnCancel);
+            this.PropertyChanged +=
+                (_, __) => SaveCommand.ChangeCanExecute();
+        }
+
+        private bool ValidateSave()
+        {
+            return !String.IsNullOrWhiteSpace(text)
+                && !String.IsNullOrWhiteSpace(description);
+        }
+
+        public string Text
+        {
+            get => text;
+            set => SetProperty(ref text, value);
+        }
+
+        public string Description
+        {
+            get => description;
+            set => SetProperty(ref description, value);
+        }
+
+        public Command SaveCommand { get; }
+        public Command CancelCommand { get; }
+
+        private async void OnCancel()
+        {
+            // This will pop the current page off the navigation stack
+            await Shell.Current.GoToAsync("..");
+        }
+
+        private async void OnSave()
+        {
+            Item newItem = new Item()
+            {
+                Id = Guid.NewGuid().ToString(),
+                Text = Text,
+                Description = Description
+            };
+
+            await DataStore.AddItemAsync(newItem);
+
+            // This will pop the current page off the navigation stack
+            await Shell.Current.GoToAsync("..");
+        }
+    }
+}