一、概述
在MVVM Light框架中，主要通过命令绑定来进行事件的处理。
WPF中，命令是通过实现 ICommand 接口创建的。 ICommand 公开了两个方法（Execute 及 CanExecute）和一个事件（CanExecuteChanged）。
在MVVM Light框架中，RelayCommand类实现了ICommand 接口，用于完成命令绑定。
通过RelayCommand类的构造函数传入Action类型的Execute委托和Func<bool>类型的CanExecute委托，CanExecute委托用于表示当前命令是否可以执行，Execute委托则表示执行当前命令对应的方法。
通过命令绑定，解耦了View和ViewModel的行为交互，将视图的显示和业务逻辑分开。比如我们对界面上的某个按钮进行命令绑定，当点击按钮的时候，实际上进行操作是在对应的ViewModel下的所绑定的方法中执行的。
二、Demo
我们模拟以下场景：
界面上有一个添加用户的按钮，一个输入用户信息的TextBox，一个用于显示添加后结果Label，一个CheckBox。
按钮使用RelayCommand进行绑定，CheckBox用于控制命令的可用性。
1 using GalaSoft.MvvmLight;
2
3 namespace MvvmLightDemo1.Model
4 {
5 public class WelcomeModel : ObservableObject
6 {
7 private string welcomeMsg;
8 public string WelcomeMsg
9 {
10 get { return welcomeMsg; }
11 set { welcomeMsg = value; RaisePropertyChanged(() => WelcomeMsg); }
12 }
13 }
14
15 }
1 using CommonServiceLocator;
2 using GalaSoft.MvvmLight.Ioc;
3
4 namespace MvvmLightDemo1.ViewModel
5 {
6 /// <summary>
7 /// This class contains static references to all the view models in the
8 /// application and provides an entry point for the bindings.
9 /// </summary>
10 public class ViewModelLocator
11 {
12 /// <summary>
13 /// Initializes a new instance of the ViewModelLocator class.
14 /// </summary>
15 public ViewModelLocator()
16 {
17 ServiceLocator.SetLocatorProvider(() => SimpleIoc.Default);
18 SimpleIoc.Default.Register<MainViewModel>();
19 }
20
21 public MainViewModel Main
22 {
23 get
24 {
25 return ServiceLocator.Current.GetInstance<MainViewModel>();
26 }
27 }
28
29 public static void Cleanup()
30 {
31 // TODO Clear the ViewModels
32 }
33 }
34 }
1 using GalaSoft.MvvmLight;
2 using GalaSoft.MvvmLight.CommandWpf;
3 using MvvmLightDemo1.Model;
4 using System.Windows.Input;
5
6 namespace MvvmLightDemo1.ViewModel
7 {
8 public class MainViewModel : ViewModelBase
9 {
10 private WelcomeModel welcomeModel;
11 public WelcomeModel WelcomeModel
12 {
13 get { return welcomeModel; }
14 set { welcomeModel = value; RaisePropertyChanged(() => WelcomeModel); }
15 }
16 /// <summary>
17 /// Initializes a new instance of the MainViewModel class.
18 /// </summary>
19 public MainViewModel()
20 {
21 WelcomeModel = new WelcomeModel() { WelcomeMsg = "Welcome to MVVMLight World!" };
22 }
23
24 private string userList = "Mary";
25
26 public string UserList
27 {
28 get { return userList; }
29 set
30 {
31 userList = value;
32 RaisePropertyChanged();
33 }
34 }
35 private string user = "";
36
37 public string User
38 {
39 get { return user; }
40 set { user = value; }
41 }
42 private bool isCanAddUser;
43
44 public bool IsCanAddUser
45 {
46 get { return isCanAddUser; }
47 set { isCanAddUser = value; }
48 }
49
50 #region Command
51 private RelayCommand addUserCommand;
52
53 public RelayCommand AddUserCommand
54 {
55 get
56 {
57 if (addUserCommand == null)
58 {
59 addUserCommand = new RelayCommand(AddUser, () => { return IsCanAddUser; });
60 }
61 return addUserCommand;
62 }
63 set { addUserCommand = value; }
64 }
65 private void AddUser()
66 {
67 UserList = UserList + " " + User;
68 }
69 #endregion
70
71 }
72 }
1 <Window x:Class="MvvmLightDemo1.MainWindow"
2 xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
3 xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
4 xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
5 xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
6 xmlns:local="clr-namespace:MvvmLightDemo1"
7 mc:Ignorable="d"
8 Title="MVVMLIghtDemo1" Height="350" Width="525" Background="#FF699DC1">
9 <Window.DataContext>
10 <Binding Path="Main" Source="{StaticResource Locator}"></Binding>
11 </Window.DataContext>
12 <Grid>
13 <StackPanel >
14 <TextBlock Text="{Binding WelcomeModel.WelcomeMsg}" FontSize="28" Foreground="#FFBB4913" HorizontalAlignment="Center"/>
15 <StackPanel Orientation="Horizontal" Visibility="Collapsed">
16 <Label Content="修改信息：" VerticalContentAlignment="Center" FontSize="20" Foreground="#FFC55D21"></Label>
17 <TextBox Text="{Binding Path=WelcomeModel.WelcomeMsg,Mode=TwoWay,UpdateSourceTrigger=PropertyChanged}" FontSize="20" Foreground="#FFBB4913"/>
18 <Button Content="LostFocus" Background="#FF22A658"></Button>
19 </StackPanel>
20
21 <StackPanel Orientation="Horizontal">
22 <Label Content="UserList：" VerticalContentAlignment="Center" FontSize="20" Foreground="#FFC55D21"></Label>
23 <Label Content="{Binding Path=UserList,Mode=TwoWay,UpdateSourceTrigger=PropertyChanged}" FontSize="20" Foreground="#FFBB4913"/>
24 </StackPanel>
25 <StackPanel Orientation="Horizontal">
26 <Label Content="UserName：" VerticalContentAlignment="Center" FontSize="20" Foreground="#FFC55D21"></Label>
27 <TextBox Width="200" Text="{Binding User, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}"></TextBox>
28 <Button Content="AddUser" Command="{Binding AddUserCommand}"></Button>
29 <CheckBox Content="IsCanAdd" VerticalAlignment="Center" FontSize="16" IsChecked="{Binding IsCanAddUser, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}"></CheckBox>
30 </StackPanel>
31
32 </StackPanel>
33 <StackPanel VerticalAlignment="Top" HorizontalAlignment="Center" >
34
35 </StackPanel>
36 </Grid>
37 </Window>
运行结果如下：