【WPF】MVVM极其简单的例子

目的：通过例子了解、理解MVVM的基本结构。

Model

namespace WpfStudy.Model
{
    public class UserModel
    {
        public string Name { get; set; }
    }
}

ViewModel

namespace WpfStudy.ViewModel
{
    public class MainVM : NotifyPropBase
    {
        public MainVM(MainWindow view)
        {
            View = view;
        }
        private MainWindow View { get; set; }

        private UserModel _userModel;

        public UserModel User
        {
            get
            {
                if (_userModel == null)
                {
                    _userModel = new UserModel();
                }
                return _userModel;
            }
            set { _userModel = value; Notify(); }
        }

        public RelayCmd ClickCmd => new RelayCmd((a) =>
        {
            MessageBox.Show(User.Name);
            User.Name = null;
            User = User;//或者使用Notify("User");
        });

        public RelayCmd CloseCmd => new RelayCmd((a) =>
        {
            View.Close();
        });
    }
}

View

xaml

    <Window.Resources>
        <Style TargetType="Button">
            <Setter Property="Width" Value="100"/>
            <Setter Property="Height" Value="30"/>
            <Setter Property="Margin" Value="0,30,0,0"/>
        </Style>
    </Window.Resources>
    <StackPanel Margin="20">
        <TextBox Text="{Binding User.Name}" Width="100" Height="40" Margin="0,0,0,20" FontSize="30"/>
        <Button Content="清空" Command="{Binding ClickCmd}"/>
        <Button Content="关闭窗口" Command="{Binding CloseCmd}"/>
    </StackPanel>

cs

namespace WpfStudy
{
    /// <summary>
    /// MainWindow.xaml 的交互逻辑
    /// </summary>
    public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();
            this.DataContext = new MainVM(this);
        }
    }
}

两个工具类

监听属性变化

    public class NotifyPropBase : INotifyPropertyChanged
    {
        public event PropertyChangedEventHandler PropertyChanged;

        public void Notify([CallerMemberName] string propertyName = "")
        {
            PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
        }
    }

监听命令

    public class RelayCmd : ICommand
    {
        public RelayCmd(Action<object> execute)
        {
            _execute = execute;
        }

        readonly Action<object> _execute;

        public event EventHandler CanExecuteChanged;

        public bool CanExecute(object parameter) => true;

        public void Execute(object parameter)
        {
            _execute?.Invoke(parameter);
        }
    }

思考

1. Model里面就写CLR属性，不搞属性值变化的监听。

2. View的cs代码也要简洁，只显式留一个构造函数，不留其他属性和方法。

3. 业务交互功能集中在ViewModel中。

4. 是在ViewModel中对Model进行监听设置，所以Model内的属性修改后，需要显式重新赋值一下Model，本质上是在ViewModel中调用Notify()并传递Model类型的属性名。

5. 还可以再VM中增加常用的Model属性，给View提供绑定，实际用的还是Model中的数据。