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 [email protected] where [email protected]";
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。
原文地址：https://www.cnblogs.com/hglSV/p/11706420.html
时间： 2024-10-14 12:20:20