WPF MVVM

WPF MVVM

MVVM=Model+View+ViewModel

• Model:现实世界中对象抽象的结果，也就是实体模型
• View:UI界面
• ViewModel:为UI界面服务的模型，可以理解为数据传输对象（DTO）
  ViewModel和View的沟通有两个方面：数据和操作
• 传递数据–使用数据属性
• 传递操作–使用命令属性
  很多人不理解MVVM和MVC的区别，我个人的理解是，MVC中的C可控范围更大，不仅可以控制View也能控制Model。而MVVM中，View是主动从ViewModel中获取数据，如果获取不到也不会导致程序崩溃，虽然VIewModel也可以去操作View，但是原则是View层主动获取数据，ViewModel是被动的提供数据。
  

案例1：

关注点：NotificationObject与数据属性
DelegateCommand与命令属性

命令的传递（单向）

class DelegateCommand : ICommand
{
    public bool CanExecute(object parameter)
    {
        if (this.CanExecuteFunc == null)
        {
            return true;
        }

        return this.CanExecuteFunc(parameter);
    }

    public event EventHandler CanExecuteChanged;

    public void Execute(object parameter)
    {
        if (this.ExecuteAction == null)
        {
            return;
        }
        this.ExecuteAction(parameter);
    }

    public Action<object> ExecuteAction { get; set; }
    public Func<object, bool> CanExecuteFunc { get; set; }
}

ViewModels

//通知Binding属性更新,供ViewModels使用的类
class NotificationObject : INotifyPropertyChanged
{
    public event PropertyChangedEventHandler PropertyChanged;
   
    public void RaisePropertyChanged(string propertyName)
    {
        //也可以这样声明，自动获取方法调用方的方法名称或属性名称
        //public void RaiseChanged([CallerMemberName]string proName=null)
        if (this.PropertyChanged != null)
        {
            this.PropertyChanged.Invoke(this, new PropertyChangedEventArgs(propertyName));
        }
    }
}

该案例只有一个MainWindow，所以创建一个MainWindowViewModel类

class MainWindowViewModel : NotificationObject
{
    private double input1;

    public double Input1
    {
        get { return input1; }
        set
        {
            input1 = value;
            this.RaisePropertyChanged("Input1");
        }
    }

    private double input2;

    public double Input2
    {
        get { return input2; }
        set
        {
            input2 = value;
            this.RaisePropertyChanged("Input2");
        }
    }

    private double result;

    public double Result
    {
        get { return result; }
        set
        {
            result = value;
            this.RaisePropertyChanged("Result");
        }
    }

    public DelegateCommand AddCommand { get; set; }
    public DelegateCommand SaveCommand { get; set; }

    private void Add(object parameter)
    {
        this.Result = this.Input1 + this.Input2;
    }

    private void Save(object parameter)
    {
        SaveFileDialog dlg = new SaveFileDialog();
        dlg.ShowDialog();
    }

    public MainWindowViewModel()
    {
        this.AddCommand = new DelegateCommand();
        this.AddCommand.ExecuteAction = new Action<object>(this.Add);

        this.SaveCommand = new DelegateCommand();
        this.SaveCommand.ExecuteAction = new Action<object>(this.Save);
    }
}

主界面

<Window x:Class="SimpleMvvmDemo.Client.MainWindow" xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" Title="MainWindow" Height="350" Width="525">
    <Grid>
        <Grid.RowDefinitions>
            <RowDefinition Height="Auto" />
            <RowDefinition Height="*" />
        Grid.RowDefinitions>
        <Menu>
            <MenuItem Header="_File">
                <MenuItem Header="_Save" Command="{Binding SaveCommand}" />
            MenuItem>
        Menu>
        <Grid Grid.Row="1">
            <Grid.RowDefinitions>
                <RowDefinition Height="Auto" />
                <RowDefinition Height="Auto" />
                <RowDefinition Height="Auto" />
                <RowDefinition Height="*" />
            Grid.RowDefinitions>
            <Slider x:Name="slider1" Grid.Row="0" Background="LightBlue" Minimum="-100" Maximum="100" Margin="4"  Value="{Binding Input1}" />
            <Slider x:Name="slider2" Grid.Row="1" Background="LightBlue" Minimum="-100" Maximum="100" Margin="4"  Value="{Binding Input2}" />
            <Slider x:Name="slider3" Grid.Row="2" Background="LightBlue" Minimum="-100" Maximum="100" Margin="4" Value="{Binding Result}" />
            <Button x:Name="addButton" Grid.Row="3" Content="Add" Width="120" Height="80" Command="{Binding AddCommand}"/>
        Grid>
    Grid>
Window>

由于Binding不指定Source默认使用了控件的DataContext，所以只需要在MainWindow中增加DataContext，子代控件便可以共享这个DataContext。

public partial class MainWindow : Window
{
    public MainWindow()
    {
        InitializeComponent();
        this.DataContext = new MainWindowViewModel();
    }
}

案例2：

项目使用了Microsoft.Practices.Prism，需要提前引用

• Models

要显示单品和饭店信息，所以定义Dish和Restaurant两个类

public class Dish : NotificationObject
{
    public string Name { get; set; }
    public string Category { get; set; }
    public string Comment { get; set; }
    public double Score { get; set; }
}
class Restaurant : NotificationObject
{
    public string Name { get; set; }
    public string Address { get; set; }
    public string PhoneNumber { get; set; }
}

• Services

具有获得菜单和点单服务，先定义相关接口，再实现类

public interface IDataService
{
    List<Dish> GetAllDishes();
}
class XmlDataService : IDataService
{
    public List<Dish> GetAllDishes()
    {
        List<Dish> dishList = new List<Dish>();
        string xmlFileName = System.IO.Path.Combine(Environment.CurrentDirectory, @"Data\Data.xml");
        XDocument xDoc = XDocument.Load(xmlFileName);
        var dishes = xDoc.Descendants("Dish");
        foreach (var d in dishes)
        {
            Dish dish = new Dish();
            dish.Name = d.Element("Name").Value;
            dish.Category = d.Element("Category").Value;
            dish.Comment = d.Element("Comment").Value;
            dish.Score = double.Parse(d.Element("Score").Value);
            dishList.Add(dish);
        }

        return dishList;
    }
}

interface IOrderService
{
    void PlaceOrder(List<string> dishes);
}
class MockOrderService : IOrderService
{
    public void PlaceOrder(List<string> dishes)
    {
        System.IO.File.WriteAllLines(@"C:\Users\cni23287938\Desktop\orders.txt", dishes.ToArray());
    }
}

• ViewModels

因为菜单后面需要具有一个是否选择项，所以要新定义一个DishMenuItemViewModel类

class DishMenuItemViewModel : NotificationObject
{
    public Dish Dish { get; set; }

    private bool isSelected;

    public bool IsSelected
    {
        get { return isSelected; }
        set
        {
            isSelected = value;
            this.RaisePropertyChanged("IsSelected");
        }
    }
}

MainWindowViewModel

class MainWindowViewModel : NotificationObject
{
    private int count;

    public int Count
    {
        get { return count; }
        set { count = value; this.RaisePropertyChanged("Count"); }
    }

    private Restaurant restaurant;

    public Restaurant Restaurant
    {
        get { return restaurant; }
        set { restaurant = value; this.RaisePropertyChanged("restaurant"); }
    }
    private List<DishMenuItemViewModel> dishMenu;

    public List<DishMenuItemViewModel> DishMenu
    {
        get { return dishMenu; }
        set { dishMenu = value; this.RaisePropertyChanged("DishMenu"); }
    }
    public DelegateCommand PlaceOrderCommand { get; set; }
    public DelegateCommand SelectMenuItemCommand { get; set; }


    public MainWindowViewModel()
    {
        LoadRestaurant();
        LoadDishMenu();
        PlaceOrderCommand = new DelegateCommand(this.PlaceOrderCommandExecute);
        SelectMenuItemCommand = new DelegateCommand(this.SelectMenuItemExecute);
    }


    private void LoadRestaurant()
    {
        this.Restaurant = new Restaurant();
        this.Restaurant.Name = "Crazy";
        this.restaurant.Address = "北京";
        this.restaurant.PhoneNumber = "1";
    }

    private void LoadDishMenu()
    {
        IDataService ds = new XmlDataService();
        var dishes = ds.GetAllDishes();
        this.dishMenu = new List<DishMenuItemViewModel>();
        foreach (var dish in dishes)
        {
            DishMenuItemViewModel item = new DishMenuItemViewModel();
            item.Dish = dish;
            this.dishMenu.Add(item);
        }
    }
    private void PlaceOrderCommandExecute()
    {
        var selectedDishes = this.dishMenu.Where(i => i.IsSelected == true).Select(i => i.Dish.Name).ToList();
        IOrderService orderService = new MockOrderService();
        orderService.PlaceOrder(selectedDishes);
        MessageBox.Show("订餐成功");
    }
    private void SelectMenuItemExecute()
    {
        Count = DishMenu.Count(i => i.IsSelected == true);
    }
}

xaml

<Window x:Class="WpfApp8.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:WpfApp8"
        mc:Ignorable="d"
        Title="{Binding Restaurant.Name}" Height="600" Width="800" WindowStartupLocation="CenterScreen">

    <Grid x:Name="Root" Margin="4">
        <Grid.RowDefinitions>
            <RowDefinition Height="Auto"/>
            <RowDefinition Height="*"/>
            <RowDefinition Height="Auto"/>
        Grid.RowDefinitions>
        <StackPanel>
            <StackPanel Orientation="Horizontal" >
                <TextBlock Text="欢迎"/>
                <TextBlock Text="{Binding Restaurant.Name}"/>
            StackPanel>
            <StackPanel Orientation="Horizontal">
                <TextBlock Text="电话"/>
                <TextBlock Text="{Binding Restaurant.PhoneNumber}"/>
            StackPanel>
            <StackPanel Orientation="Horizontal">
                <TextBlock Text="地址"/>
                <TextBlock Text="{Binding Restaurant.Address}"/>
            StackPanel>
        StackPanel>
        <DataGrid AutoGenerateColumns="False" CanUserDeleteRows="False" CanUserAddRows="False" Grid.Row="1" ItemsSource="{Binding DishMenu}">
            <DataGrid.Columns>
                <DataGridTextColumn Header="菜品" Binding="{Binding Dish.Name}" Width="120"/>
                <DataGridTextColumn Header="种类" Binding="{Binding Dish.Category}" Width="120"/>
                <DataGridTextColumn Header="点评" Binding="{Binding Dish.Comment}" Width="120"/>
                <DataGridTextColumn Header="推荐分数" Binding="{Binding Dish.Score}" Width="120"/>
                <DataGridTemplateColumn Header="选中" SortMemberPath="IsSelected" Width="120">
                    <DataGridTemplateColumn.CellTemplate>
                        
                        <DataTemplate>
                            <CheckBox IsChecked="{Binding Path=IsSelected,UpdateSourceTrigger=PropertyChanged}" Command="{Binding Path=DataContext.SelectMenuItemCommand,RelativeSource={RelativeSource Mode=FindAncestor,AncestorType={x:Type DataGrid}}}"/>
                        DataTemplate>
                    DataGridTemplateColumn.CellTemplate>
                DataGridTemplateColumn>
            DataGrid.Columns>
        DataGrid>
        <StackPanel Grid.Row="2">
            <TextBlock Text="共计："/>
            <TextBox IsReadOnly="True" Text="{Binding Count}"/>
            <Button Content="Order" Command="{Binding PlaceOrderCommand}"/>
        StackPanel>
    Grid>
Window>