添加项目文件。

XXCpzs/ViewModels/BaseViewModel.cs

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+using System;
+using System.Collections.Generic;
+using System.ComponentModel;
+using System.Runtime.CompilerServices;
+
+using Xamarin.Forms;
+
+using XXCpzs.Models;
+using XXCpzs.Services;
+
+namespace XXCpzs.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
+
+        protected void RaisePropertyChanged([CallerMemberName] string propertyName = "")
+        {
+            PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
+        }
+    }
+}