一篇文章，带你玩转MVVM，Dapper，AutoMapper

一、背景

由于现在做的项目都是采用WPF来进行UI设计，开发过程中都是基于MVVM来进行开发，但是项目中的MVVM并不是真正的把实体和视图进行解耦，而是将实体和视图完全融合起来，ViewModel只是用来实现View和Model的数据同步，违背了MVVM设计的数据双向绑定的初衷，完全没有发挥出MVVM的优势。

二、MVVM基本概念

1.M:表示Model，也就是一个实体对象。

2.V:表示VIew，也就是UI界面展示，即人机交互界面。

3.ViewModel：可以理解为搭建View和Model的一个业务逻辑桥梁。

三、Demo来说明

首先建立解决方案，方案框架如下：

在Models中创建一个Model实体对象Contacts

public class Contacts
    {
        public int ID { get; set; }

        public string FirstName { get; set; }
        public string LastName { get; set; }
        public string Email { get; set; }
        public string Company { get; set; }
        public string Title { get; set; }
    }

接下来我们在ViewModel中实现V和M的完全解耦，在ViewModels中添加ContractsViewModels

 public class ContractsViewModels : BaseViewModels
    {
       public  Contacts contracts = null;
        public ContractsViewModels(Contacts contracts)
        {
            this.contracts = contracts;
        }
        public ContractsViewModels()
        {
            contracts = new Contacts();
        }

        public int ID { get { return contracts.ID; } set { contracts.ID = value; OnPropertyChanged(this, nameof(ID)); } }
       
        public string FirstName { get { return contracts.FirstName; } set { contracts.FirstName = value; OnPropertyChanged(this, nameof(FirstName)); } }
       
        public string LastName { get { return contracts.LastName; } set { contracts.LastName = value; OnPropertyChanged(this, nameof(LastName)); } }
      

        public string Email { get { return contracts.Email; } set { contracts.Email = value; OnPropertyChanged(this, nameof(Email)); } }
      
        public string Company { get { return contracts.Company; } set { contracts.Company = value; OnPropertyChanged(this, nameof(Company)); } }

      
        public string Title { get { return contracts.Title; } set { contracts.Title = value; OnPropertyChanged(this, nameof(Title)); } }


    }

当数据双向绑定时，视图知道自己绑定了那个实体，为了让实体的属性改变中，能够通知绑定的View，我们需要实现INotifyPropertyChanged这个接口，具体实现如下

 public class BaseViewModels : INotifyPropertyChanged
    {
        public event PropertyChangedEventHandler PropertyChanged;
        protected void OnPropertyChanged(object sender, string name)
        {
            if (PropertyChanged != null)
            {
                PropertyChanged(sender ?? this, new PropertyChangedEventArgs(name));
            }
        }
    }

以上实现，在ViewModel中改变属性，便可以轻松的通知到绑定时View控件，真正意义上实现了双向数据绑定。

接下来在ViewModel中添加ContractsVMServices来方便View的数据操作

 代码如下：

  /// <summary>
    /// ContractsViewModels服务类
    /// </summary>
    public class ContractsVMServices
    {
        /// <summary>
        /// 加载所有数据的事件
        /// </summary>
        public event EventHandler OnLoadAllContracts;
        /// <summary>
        /// 数据集合对象
        /// </summary>
        public ObservableCollection<ContractsViewModels> ContractsViewModels { get; private set; }
        /// <summary>
        /// 单个实体的事件
        /// </summary>
        public event EventHandler OnLoadContracts;
        /// <summary>
        /// 单个实体
        /// </summary>
        public ContractsViewModels ContractsViewModel { get; private set; }
        
        private ContractsVMServices() { }

        public static ContractsVMServices Instances = new ContractsVMServices();
        /// <summary>
        /// 初始化
        /// </summary>
        public void Init()
        {
            ContractsViewModels = new ObservableCollection<ContractsViewModels>();
            ContractsViewModel = new ContractsViewModels(new Contacts());
            OnLoadAllContracts?.Invoke(this, EventArgs.Empty);
            OnLoadContracts?.Invoke(this, EventArgs.Empty);
            AutoMapperWrapper.Start();
            LoadAllContracts();
        }
        /// <summary>
        /// 定时模拟数据改变
        /// </summary>
        /// <param name="afterSecond"></param>
        /// <param name="freSecond"></param>
        public void ChangeByTime(int afterSecond = 5, int freSecond = 2)
        {
            Task.Run(async () =>
            {
                await Task.Delay(afterSecond * 1000);
                while (true)
                {
                    try
                    {
                        foreach (var item in ContractsViewModels)
                        {
                            item.Title = "Change" + DateTime.Now.ToString();
                            string update = "Update contacts set Title=@Title where ID=@ID";
                            List<KeyValuePair<string, object>> ls = new List<KeyValuePair<string, object>>();
                            ls.Add(new KeyValuePair<string, object>(nameof(item.Title), item.Title));
                            ls.Add(new KeyValuePair<string, object>(nameof(item.ID), item.ID));

                            DapperHelper.Update(update, ls);

                        }
                        //string insert = @"Update into contacts (Id,FirstName,LastName,Email,Company,Title) values(@Id,@FirstName,@LastName,@Email,@Company,@Title)";

                    }
                    catch (Exception ex)
                    {
                    }
                    finally
                    {
                        await Task.Delay(freSecond * 1000);
                    }
                }

            });
        }
        /// <summary>
        /// 从数据库中加载所有数据
        /// </summary>
        private void LoadAllContracts()
        {
            try
            {
                //Task.Run(() =>
                //{
                ContractsViewModels.Clear();
                List<Contacts> contracts = DBDapper.DapperHelper.Query<Contacts>("Contacts");


                // ContractsViewModels = AutoMapperWrapper.Map<List<Contacts>, ObservableCollection<ContractsViewModels>>(contracts);
                foreach (var item in contracts)
                {
                    //ContractsViewModels models= AutoMapperWrapper.Map<Contacts, ContractsViewModels>(item);

                    ContractsViewModels.Add(new ViewModels.ContractsViewModels(item));
                }
                //});
            }
            catch (Exception ex)
            {
                Console.WriteLine(  ex.ToString());
             
            }
        }
        /// <summary>
        /// 根据ID来加载指定数据
        /// </summary>
        /// <param name="id"></param>
        public void LoadOnContracts(int id)
        {
            ContractsViewModel = ContractsViewModels.Where(obj => obj.ID == id).FirstOrDefault();
        }
        /// <summary>
        /// 创建一个新的对象
        /// </summary>
        public void Add()
        {
            try
            {
                int id = ContractsViewModels.Count > 0 ? ContractsViewModels[ContractsViewModels.Count - 1].ID + 1 : 0;
                string insert = @"insert into contacts (Id,FirstName,LastName,Email,Company,Title) values(@Id,@FirstName,@LastName,@Email,@Company,@Title)";
                int res = DapperHelper.Insert<Contacts>(insert, new List<Contacts>() { new Contacts() { ID =id, FirstName = "123", LastName = "456", Email = "123", Company = "1324", Title = "444" } });
                if (res > 0)
                {
                    LoadAllContracts();
                }
            }
            catch (Exception ex)
            {

                Console.WriteLine(ex.ToString());
            }
        }
        /// <summary>
        /// 删除对象
        /// 为了方便演示我只删除数据集合中的第一个对象
        /// </summary>
        public void Delete()
        {
            try
            {
                if (ContractsViewModels.Count > 0)
                {
                    string delete = "delete from Contacts where ID= @ID";
                    int res = DapperHelper.Delete(delete, new { ID = ContractsViewModels[0].ID });
                    if (res > 0)
                    {
                        LoadAllContracts();
                    }
                }
            }
            catch (Exception ex)
            {

                Console.WriteLine(ex.ToString());

            }
        }


        
    }

实现数据库的CRUD操作，我这里主要用到半自动化的ORM----Dapper。

老生常谈，首先需要从Nuget中安装Dapper，安装到DBDapper项目中。

或者在控制台中输入： Install -Package Dapper 完成Dapper下载安装。

创建一个DapperHelper帮助类

  public class DapperHelper
    {
        //三部曲
        //第一步：使用连接字符串创建一个IDBConnection对象；
        static IDbConnection conn = new SqlConnection(System.Configuration.ConfigurationManager.ConnectionStrings["SqlServerConnString"].ToString());
        //第二步：编写一个查询并将其存储在一个普通的字符串变量中；
        public static  void test()
        {
            string query = "SELECT * from contacts;";
            List<Contacts> contracts=(List<Contacts>)conn.Query<Contacts>(query);
            Console.WriteLine( contracts.Count);
        }

        public static  List<T> Query<T>(string typeofName)
        {
            string query = $"SELECT * from {typeofName};";
            List<T> contracts = (List<T>)conn.Query<T>(query);
            return contracts;
        }

        public static  int Insert<T>(string sql,IEnumerable<T> ls)
        {
            try
            {
              return   conn.Execute(sql, ls);
            }
            catch (Exception ex)
            {

                throw new Exception(ex.ToString());
            }
               
        }
        public static int Update(string sql, IEnumerable<KeyValuePair<string,object>> ls)
        {
            try
            {
                return conn.Execute(sql, ls);
            }
            catch (Exception ex)
            {

                throw new Exception(ex.ToString());
            }

        }


        public static int Delete(string sql, object obj)
        {
            try
            {
                return conn.Execute(sql, obj);
            }
            catch (Exception ex)
            {

                throw new Exception(ex.ToString());
            }
        }
        //public static int Update<T>(string sql, List<T> ls)
        //{

        //}
        //第三步：调用db.execute()并传递查询，完成。
    }

看上面的三步曲，和ADO.net大同小异，不过我们再也不用将数据库表的数据转换成实体了，采用Dapper便傻瓜式的转换了。

看我们的代码，我们会发现，Model跟View完全独立，不过这个时候，ViewModel会多出跟Model一样的一个实体出来，为了实现Model到ViewModel的一个完美映射，我这里采用了AutoMapper来实现映射。

老套路，我们从Nuget中下载AutoMapper，安装到ViewModels。

 或者在控制台中输入： Install -Package AutoMapper完成AutoMapper下载安装。

在ViewModels中建立AutoMapper的一个包装类AutoMapperWrapper，AutoMapper需要初始化应映射规则，因此我们需要先创建一个映射

public class SourceProfile : MapperConfigurationExpression
    {
        public SourceProfile()
        {
            base.CreateMap<ContractsViewModels, Contacts>();
            base.CreateMap<Contacts, ContractsViewModels>();
            //base.CreateMap<ContractsViewModels,Models.Contracts>();
        }
    }

AutoMapperWrapper如下：

public class AutoMapperWrapper
    {
        //protected DTOObject Result { get; set; }

        //protected IEnumerable<DTOObject> Results { get; set; }
        static   Mapper mapper = null;
        public static void Start()
        {
            MapperConfiguration configuration = new MapperConfiguration(new SourceProfile());
            mapper =  new Mapper(configuration);
           // mapper.Map<,>
          //  Mapper
            //new SourceProfile();
        }
        public static T Map<S, T>(S soure)
        {
            T to = mapper.Map<S, T>(soure);

            return to;
        }

    }

以上我们便实现了一个ViewModel,DB的后台管理。接下来我们来看一个View怎么实现数据的绑定

先看一下代码

<Window x:Class="View.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:local="clr-namespace:View"
        mc:Ignorable="d"
        Title="MainWindow" Height="450" Width="800" Loaded="Window_Loaded">
    <Grid>
        <DataGrid x:Name="datagrid" ItemsSource="{Binding ContractsViewModels}" AutoGenerateColumns="False" HorizontalAlignment="Left" Height="273" Margin="72,70,0,0" VerticalAlignment="Top" Width="415">
            <DataGrid.Columns>
                <DataGridTextColumn Header="ID" Binding="{Binding ID}"></DataGridTextColumn>
                <DataGridTextColumn Header="FirstName" Binding="{Binding FirstName}"></DataGridTextColumn>
                <DataGridTextColumn Header="LastName" Binding="{Binding LastName}"></DataGridTextColumn>
                <DataGridTextColumn Header="Email" Binding="{Binding Email}"></DataGridTextColumn>
                <DataGridTextColumn Header="Company" Binding="{Binding Company}"></DataGridTextColumn>
                <DataGridTextColumn Header="Title" Binding="{Binding Title}"></DataGridTextColumn>
                
            </DataGrid.Columns>
        </DataGrid>
        <Button x:Name="btn_LoadAll" Content="加载所有Contract数据" HorizontalAlignment="Left" Margin="97,372,0,0" VerticalAlignment="Top" Click="btn_LoadAll_Click"/>
        <Button x:Name="btn_ChangeByTime" Content="定时改变" HorizontalAlignment="Left" VerticalAlignment="Top" Width="75" Margin="284,372,0,0" Click="btn_ChangeByTime_Click"/>
        <Button x:Name="btn_Delete" Content="删除" HorizontalAlignment="Left" Margin="417,372,0,0" VerticalAlignment="Top" Width="75" Click="btn_Delete_Click"/>
        <TextBox x:Name="textBox" HorizontalAlignment="Left" Height="23" Margin="591,144,0,0" TextWrapping="Wrap" Text="{Binding ContractsViewModel.FirstName,Mode=TwoWay,UpdateSourceTrigger=PropertyChanged}" VerticalAlignment="Top" Width="120"/>
        <Label Content="FirstName" HorizontalAlignment="Left" Margin="506,141,0,0" VerticalAlignment="Top"/>

    </Grid>
</Window>

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Navigation;
using System.Windows.Shapes;

namespace View
{
    /// <summary>
    /// MainWindow.xaml 的交互逻辑
    /// </summary>
    public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();
        }

        private void Window_Loaded(object sender, RoutedEventArgs e)
        {
            try
            {
                ViewModels.ContractsVMServices.Instances.OnLoadAllContracts += (s, es) => {
                    this.Dispatcher.InvokeAsync(() => datagrid.DataContext = s);
                };
                ViewModels.ContractsVMServices.Instances.OnLoadContracts += (s, es) => {
                    this.Dispatcher.InvokeAsync(() => textBox.DataContext = s);
                };
                ViewModels.ContractsVMServices.Instances.Init();
                ViewModels.ContractsVMServices.Instances.LoadOnContracts(0);
            }
            catch (Exception ex)
            {

               
            }
        }

        private void btn_LoadAll_Click(object sender, RoutedEventArgs e)
        {
            ViewModels.ContractsVMServices.Instances.Add();
        }

        private void btn_ChangeByTime_Click(object sender, RoutedEventArgs e)
        {
            ViewModels.ContractsVMServices.Instances.ChangeByTime();
        }

        private void btn_Delete_Click(object sender, RoutedEventArgs e)
        {
            ViewModels.ContractsVMServices.Instances.Delete();

        }
    }
}

以上我们看到DataGrid的ItemsSource必须要先绑定一个源，这个源的名称跟我们ViewModel中的数据集合是一致的。修改TextBox中的数据的时候我们发现DataGrid的数据也跟着改变。以上就是实现V与M的一个解耦。