5.3 MVVM模型

一、MVVM的基本概念

MVVM的基本概念：Model、View、ViewModel

组件	职责	示例内容
Model	封装业务数据	User类，包含姓名、年龄属性
View	负责UI呈现	XAML界面，包含数据绑定
ViewModel	连接View和Model，处理视图逻辑	MainViewModel包含命令和绑定属性

二、例子：

2.1.Model

  // Models/User.cs
  public class User : INotifyPropertyChanged
  {
      private string _name;
      private int _age;

      public string Name
      {
          get => _name;
          set
          {
              _name = value;
              OnPropertyChanged(nameof(Name));
          }
      }

      public int Age
      {
          get => _age;
          set
          {
              _age = value;
              OnPropertyChanged(nameof(Age));
          }
      }
      public event PropertyChangedEventHandler PropertyChanged;
      protected virtual void OnPropertyChanged( string propertyName  )
      {
          PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
      }
  }

2.2 ViewModel

  // ViewModels/MainViewModel.cs
  public class MainViewModel : INotifyPropertyChanged
  {
      private User _user = new User { Name = "张三", Age = 25 };

      public User User
      {
          get => _user;
          set
          {
              _user = value;
              OnPropertyChanged(nameof(User));
          }
      }
      // 命令定义
      public ICommand SaveCommand
      {
          get
          {
              return new RelayCommand(SaveUser,  CanSaveExecute);
          }
      }
     bool CanSaveExecute()
      {
          return true;
      }

      private void SaveUser()
      {
          MessageBox.Show($"保存成功：{User.Name}, {User.Age}");
      }

      public event PropertyChangedEventHandler PropertyChanged;

      protected virtual void OnPropertyChanged(string propertyName )
      {
          PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
      }
  }

2.3  ICommand （基本都是格式化的）

 public class RelayCommand : ICommand
 {
     private readonly Action _execute;
     private readonly Func<bool> _canExecute;

     public RelayCommand(Action execute, Func<bool> canExecute = null)
     {
         _execute = execute;
         _canExecute = canExecute;
     }

     public bool CanExecute(object parameter)
     {
         if (_canExecute == null)
         {
             return true;
         }
         else
             return _canExecute();
     }

     public void Execute(object parameter) => _execute();

     public event EventHandler CanExecuteChanged
     {
         add
         {
             if(_canExecute!=null)
             {
                 CommandManager.RequerySuggested += value;
             }                
         }
         remove
         {
             if (_canExecute != null)
             {
                 CommandManager.RequerySuggested -= value;
             }
         }           
     }
 }

2.4 调用

 public partial class Window1 : Window
 {
     //   public PersonViewModel m_PersonViewModel = new PersonViewModel();

     public MainViewModel model = new MainViewModel();
     public Window1()
     {
         InitializeComponent();
         DataContext = model;
     }
}

 <StackPanel Margin="15">
     <TextBox Text="{Binding User.Name,Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}"
              Margin="0,0,0,10"/>

     <TextBox Text="{Binding User.Age, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}"
              Margin="0,0,0,10"/>

     <Button Content="保存" 
             Command="{Binding SaveCommand}"
             Padding="10,5"/>
 </StackPanel>