事件是一种编程结构,它对状态的变化作出反应,通知任何已注册通知的端点.主要地,事件用于通过鼠标和键盘通知用户输入,但是它们的用途不限于此.每当检测到状态更改时,可能在加载或初始化对象时,可以触发事件以提醒任何感兴趣的第三方.
在使用MVVM(Model-View-ViewModel)设计模式的WPF应用程序中,视图模型是负责处理应用程序的表示逻辑和状态的组件.
视图的代码隐藏文件不应包含任何代码来处理从任何用户界面(UI)元素(如Button或ComboBox)引发的事件,也不应包含任何特定于域的逻辑./p>
理想情况下,View的代码隐藏只包含一个调用InitializeComponent方法的构造函数,也许还有一些额外的代码来控制或与视图层交互在XAML中表达困难或低效,例如复杂的动画.
让我们看看我们的应用程序中按钮点击事件的一个简单示例.以下是MainWindow.xaml文件的XAML代码,您将在其中看到两个按钮.
<Window x:Class = "MVVMHierarchiesDemo.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:MVVMHierarchiesDemo" xmlns:views = "clr-namespace:MVVMHierarchiesDemo.Views" xmlns:viewModels = "clr-namespace:MVVMHierarchiesDemo.ViewModel" mc:Ignorable = "d" Title = "MainWindow" Height = "350" Width = "525"> <Window.DataContext> <local:MainWindowViewModel/> </Window.DataContext> <Window.Resources> <DataTemplate DataType = "{x:Type viewModels:CustomerListViewModel}"> <views:CustomerListView/> </DataTemplate> <DataTemplate DataType = "{x:Type viewModels:OrderViewModel}"> <views:OrderView/> </DataTemplate> </Window.Resources> <Grid> <Grid.RowDefinitions> <RowDefinition Height = "Auto" /> <RowDefinition Height = "*" /> </Grid.RowDefinitions> <Grid x:Name = "NavBar"> <Grid.ColumnDefinitions> <ColumnDefinition Width = "*" /> <ColumnDefinition Width = "*" /> <ColumnDefinition Width = "*" /> </Grid.ColumnDefinitions> <Button Content = "Customers" Command = "{Binding NavCommand}" CommandParameter = "customers" Grid.Column = "0" /> <Button Content = "Order" Command = "{Binding NavCommand}" CommandParameter = "orders" Grid.Column = "2" /> </Grid> <Grid x:Name = "MainContent" Grid.Row = "1"> <ContentControl Content = "{Binding CurrentViewModel}" /> </Grid> </Grid> </Window>
您可以看到上面的XAML文件中没有使用按钮Click属性,但按下按钮时Command和CommandParameter属性用于加载不同的视图.现在,您需要在MainWindowViewModel.cs文件中定义命令实现,但不要在View文件中定义.以下是完整的MainWindowViewModel实现.
using MVVMHierarchiesDemo.ViewModel; using MVVMHierarchiesDemo.Views; using System; using System.Collections.Generic; using System.Linq; using System.Text; using System.Threading.Tasks; namespace MVVMHierarchiesDemo { class MainWindowViewModel : BindableBase { public MainWindowViewModel() { NavCommand = new MyICommand<string>(OnNav); } private CustomerListViewModel custListViewModel = new CustomerListViewModel(); private OrderViewModel orderViewModelModel = new OrderViewModel(); private BindableBase _CurrentViewModel; public BindableBase CurrentViewModel { get { return _CurrentViewModel; } set { SetProperty(ref _CurrentViewModel, value); } } public MyICommand<string> NavCommand { get; private set; } private void OnNav(string destination) { switch (destination) { case "orders": CurrentViewModel = orderViewModelModel; break; case "customers": default: CurrentViewModel = custListViewModel; break; } } } }
从BindableBase类派生所有ViewModel.编译并执行上面的代码时,您将看到以下输出.
如您所见,我们在MainWindow上只添加了两个按钮和一个CurrentViewModel.现在,如果您单击任何按钮,它将导航到该特定视图.让我们点击Customers按钮,你会看到显示了CustomerListView.
我们建议您逐步执行上述示例,以便更好地理解.