添加项目文件。

TodoList/Services/IDataService.cs

@@ -0,0 +1,14 @@
+using System.Collections.Generic;
+using System.Threading.Tasks;
+using TodoList.Models;
+
+namespace TodoList.Services
+{
+    public interface IDataService
+    {
+        Task<List<TodoItem>> LoadTasksAsync();
+        Task SaveTaskAsync(TodoItem task);
+        Task SaveAllAsync(List<TodoItem> tasks);
+        Task DeleteTaskAsync(string id);
+    }
+}