3

一 学习前提:

(1)Data Binding
(2)Dependency Property
(3)委托、事件、命令ICommand
上面三点内容,在学习MVVM之前要求简单了解并掌握使用。

MVVM介绍

MVC,Model - View - Controller的模式,页面和代码分离的写法,MVVM:Model - View - ViewModel,和WPF很好的进行结合,View负责界面,主要是写.xaml的文件,Model是一些实体类;ViewModel是联系两者的关键,并分离两者;
View需要什么,ViewModel就提供什么,如果将View理解为界面,Model和ViewModel以及Service等理解为后台的话,那么界面和后台是没有任何关系的,界面开发人员只要告诉后台人员需要哪些对象/属性,就可以进行开发了,二者之间的结合通过Binding操作进行绑定,解耦效果优于MVC,架构图如下:

clipboard.png
几个重要的概念:
1、属性
1)数据绑定源:CLR对象、动态对象、ADO.NET 对象、XML对象、DependencyObject对象
2)命令属性:ICommand、
3) 集合对象绑定:ObservableCollection<T>;
2、NotificationObject类
3、ICommand接口

    MVVM的难点和重点在于View以及MiewModel之间的绑定。

三 项目实战

效果如下:
按照上述架构图新建目录如下:

clipboard.png

按照从底层到显示层的策略:
(1)Data

<?xml version="1.0" encoding="utf-8" ?>
<Dishes>
  <Dish>
    <Name>土豆泥底披萨</Name>
    <Category>披萨</Category>
    <Comment>本店特色</Comment>
    <Score>4.5</Score>
  </Dish>
  <Dish>
    <Name>烤囊底披萨</Name>
    <Category>披萨</Category>
    <Comment>本店特色</Comment>
    <Score>5</Score>
  </Dish>
  <Dish>
    <Name>水果披萨</Name>
    <Category>披萨</Category>
    <Comment></Comment>
    <Score>4</Score>
  </Dish>
  <Dish>
    <Name>牛肉披萨</Name>
    <Category>披萨</Category>
    <Comment></Comment>
    <Score>5</Score>
  </Dish>
</Dishes>

(2)Model

//定义Model,用于和xml文档中的节点属性匹配 
class Dish
{
    public string Name { get; set; }
    public string Category { get; set; }
    public string Comment { get; set; }
    public double Score { get; set; }
}
class Restaurant 
{
    public string Name { get; set; }
    public string Address { get; set; }
    public string PhoneNumber { get; set; }
}

(3)Service
接口:

interface IDataService
{
    List<Dish> GetAllDishes();
}
interface IOrderService
{
    void PlaceOrder(List<string> dishes);
}

实现:

class XmlDataService:IDataService
{        
    public List<Dish> GetAllDishes()
    {
        //读取Dish集合,用于接收数据并返回值
        List<Dish> dishList = new List<Dish>();
        //读取XML文件路径
        string xmlFileName = System.IO.Path.Combine(Environment.CurrentDirectory, @"Data\Data.xml");
        //加载xml文件
        XDocument xDoc = XDocument.Load(xmlFileName);
        //按照顺序返回<Dishes>集合下<Dish>标签里的所有内容
        var dishes = xDoc.Descendants("Dish");
        //将xml筛选的集合里的属性与Model对象绑定
        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);
            //添加到List集合
            dishList.Add(dish);
        }
        return dishList;
    }
}
class MockOrderService:IOrderService
{
    public void PlaceOrder(List<string> dishes)
    {
        System.IO.File.WriteAllLines(@"C:\order.txt", dishes.ToArray());
    }
}

至此,静态的代码编写完毕,无论是使用什么类型的框架,这部分东西大同小异。
(4)ViewModels

class DishMenuItemViewModel:NotificationObject
{
    public Dish Dish { get; set; }
    //将IsSelected属性和Dish中的属性一起作为DishMenuItemViewModel里的属性
    private bool isSelected;
    public bool IsSelected
    {
        get { return isSelected; }
        set
        {
            //RaisePropertyChanged方法,源于引入属性更改通知类
            isSelected = value;
            this.RaisePropertyChanged("IsSeleted");//"IsSelected"属性值变化之后,自动通知使用该属性的方法,有点观察者模式的意思
        }
    }
}
class MainWindowViewModel : NotificationObject
{
    public DelegateCommand PlaceOrderCommand { get; set; }
    public DelegateCommand SelectMenuItemCommand { get; set; }
    public DelegateCommand RemoveItemCommand { get; set; }
    private double count;
    //数据属性-Count
    public double Count
    {
        get { return count; }
        set
        {
            count = value;
            this.RaisePropertyChanged("Count");
        }
    }

    private Restaurant restaurant;
    //数据属性-Restaurant
    public Restaurant Restaurant
    {
        get { return restaurant; }
        set
        {
            restaurant = value;
            this.RaisePropertyChanged("Restaurant");
        }
    }

    private ObservableCollection<DishMenuItemViewModel> dishMenu;

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

    public MainWindowViewModel()
    {
        this.LoadRestaurant();
        this.LoadDishMenu();
        //单向"命令属性"的加载过程,通过实例化委托的形式
        this.PlaceOrderCommand = new DelegateCommand();
        this.PlaceOrderCommand.ExecuteAction = new Action<object>(this.PlaceOrderCommandExecute);
        this.SelectMenuItemCommand = new DelegateCommand();
        this.SelectMenuItemCommand.ExecuteAction = new Action<object>(this.SelectMenuItemExecute);
        this.RemoveItemCommand = new DelegateCommand();
        this.RemoveItemCommand.ExecuteAction = new Action<object>(this.RemoveItem);
    }


    private void LoadRestaurant()
    {
        this.Restaurant = new Restaurant();
        this.Restaurant.Name = "茶馆餐厅";
        this.restaurant.Address = "北京市乐客灵境科技有限公司";
        this.Restaurant.PhoneNumber = "12345678900";
    }

    private void LoadDishMenu()
    {
        IDataService ds = new XmlDataService();
        var dishes = ds.GetAllDishes();
        //为数据属性赋值
        this.DishMenu = new ObservableCollection<DishMenuItemViewModel>();
        foreach (var dish in dishes)
        {
            DishMenuItemViewModel item = new DishMenuItemViewModel();
            item.Dish = dish;
            item.IsSelected = false;
            this.DishMenu.Add(item);
        }
    }

    private void PlaceOrderCommandExecute(object parameter)
    {
        //lamad表达式的形式来选取所需要的数据
        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(object parameter)
    {
        this.Count = this.DishMenu.Count(i => i.IsSelected == true);
    }     

    private void RemoveItem(object parameter)
    {            
        this.DishMenu.RemoveAt(0);//移除第一项
        SelectMenuItemExecute(parameter);//更新Count值
    }        
}

其中DelegateCommand就是继承ICommand而来,包括二个方法和一个事件:

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; }
}

其实会发现,在ViewModel当中并没有很强的业务逻辑,业务逻辑更多的是放到Service当中的,在ViewModel当中所存放的内容,更多的会是一些属性,包括命令属性、数据属性,这些用于和View进行绑定,通过Binding,发现,后台的数据改变了,直接就会在前台页面上更新,这就是MVVM + WPF的魅力之一。同时也要知道,View和ViewModel之间的绑定,也是使用这个框架的难点之一。
(5)View
通过对控件的属性、样式进行设置.
通过Binding和后台数据进行绑定.

 <Grid>        
        <Border Grid.Row="0" BorderBrush="Orange" BorderThickness="3" CornerRadius="6" Background="Yellow">
            <Grid>
                <Grid.RowDefinitions>
                    <RowDefinition Height="auto"/>
                    <RowDefinition Height="*"/>
                    <RowDefinition Height="auto"/>
                </Grid.RowDefinitions>
                <TextBlock FontSize="18"  FontFamily="Bolt">订餐系统:</TextBlock>
                <DataGrid AutoGenerateColumns="False" GridLinesVisibility="None" CanUserDeleteRows="False"
                        CanUserAddRows="False" Margin="0,4" Grid.Row="1" FontSize="16" 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}"
                                            VerticalAlignment="Center" HorizontalAlignment="Center"
                                            Command="{Binding Path=DataContext.SelectMenuItemCommand, RelativeSource={RelativeSource Mode=FindAncestor, AncestorType={x:Type DataGrid}}}" />
                                </DataTemplate>
                            </DataGridTemplateColumn.CellTemplate>
                        </DataGridTemplateColumn>
                    </DataGrid.Columns>
                </DataGrid>
                <Grid   Grid.Row="2" >
                    <!--<StackPanel  HorizontalAlignment="Left" Orientation="Horizontal" VerticalAlignment="Center">
                        <TextBlock>不能选取的菜名:</TextBlock>
                        <CheckBox Name="_cbNo1">牛肉披萨</CheckBox>
                        <CheckBox Name="_cbNo2">水果披萨</CheckBox>
                    </StackPanel>-->                    
                    <StackPanel  HorizontalAlignment="Right" Orientation="Horizontal">
                        
                        <TextBlock Text="共计" VerticalAlignment="Center" />
                        <TextBox IsReadOnly="True" TextAlignment="Center" Width="120" Text="{Binding Count}" Margin="4,0" />
                        <Button Content="Order" Height="24" Width="120" Command="{Binding PlaceOrderCommand}" />
                    </StackPanel>
                </Grid>                
            </Grid>            
        </Border>
    </Grid>

此时会发现,在View的.cs代码里,没有类似于onClick(),这样的方法,都通过绑定实现自动更新了。
(6)设置View的数据来源

public MainWindow()
{
    InitializeComponent();
    this.DataContext = new MainWindowViewModel();
}

在View的.cs文件中,通过this.DataContext = new MainWindowViewModel();的方式,绑定该View的数据来自于哪个ViewModel。
ps:另外,主要参考文章http://blog.csdn.net/zzh92062...
我做了代码演示并进行一些扩展,主要在于把List<T>绑定更改为ObservableCollection<T>。就不会出现在List中移除一项,界面不自动更新的bug,各位可尝试,还可进行CanExecuteChanged的尝试。

  至此,MVVM框架的简单实用,就通过这个例子实现了。
  That's all.

李志玮
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求索~~