视图：我有usercontrol，它具有文本框和标签。当“ Enter”键关闭时，我希望标签使用文本框的值表单更新。为了这个示例，我创建了一个CaruserControl。我将在MainWindow的ItemScontrol中托管这些列表。

模型：我有班车，这将是模型。

ViewModel：我没有Carusercontrol和汽车的ViewModel。我为MainWindow提供了一个 - 我们将其称为MainViewModel。

我可以从各个usercontrols到MainViewModel传播命令，但是我不确定从MainViewModel中的文本框中获取值吗？

以下是我从我在线阅读的有关MVVM的内容中做出的一些假设（当然有一些来源说假设是错误的）。

1] USERCONTROL不应具有ViewModel。

2] USERCONTROL只能揭示依赖性属性，而不应具有InotifyChanged或事件的公共属性。

因此，问题是，如何更新标签，并在MainViewModel中访问文本框值。

这是测试代码：

----- carusercontrol.xaml ----

<UserControl x:Class="TestMVVM.CarUserControl"             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"              xmlns:d="http://schemas.microsoft.com/expression/blend/2008"              xmlns:local="clr-namespace:TestMVVM"             mc:Ignorable="d"              d:DesignHeight="50" d:DesignWidth="300" x:Name="thisUC">    <Grid>        <Grid.ColumnDefinitions>            <ColumnDefinition Width="*"/>            <ColumnDefinition Width="*"/>        </Grid.ColumnDefinitions>        <Label Grid.Column="0">--</Label>        <TextBox Grid.Column="1" Background="#FFE8D3D3" BorderThickness="0">            <TextBox.InputBindings>                <KeyBinding Key="Enter"                                 Command="{Binding KeyDownCommand, ElementName=thisUC}"                                 CommandParameter="{Binding}"/>            </TextBox.InputBindings>        </TextBox>    </Grid></UserControl>

----- carusercontrol.cs -----------------

using System;using System.Collections.Generic;using System.Linq;using System.Text;using System.Threading.Tasks;using System.Windows;using System.Windows.Controls;using System.Windows.Data;using System.Windows.Documents;using System.Windows.Input;using System.Windows.Media;using System.Windows.Media.Imaging;using System.Windows.Navigation;using System.Windows.Shapes;namespace TestMVVM{    /// <summary>    /// Interaction logic for CarUserControl.xaml    /// The Usercontrol    /// </summary>    public partial class CarUserControl : UserControl    {        private static readonly DependencyProperty StrValueProperty = DependencyProperty.Register("StrValue", typeof(float), typeof(CarUserControl), new PropertyMetadata(null));        private static readonly DependencyProperty KeyDownCommandProperty = DependencyProperty.Register("KeyDownCommand", typeof(ICommand), typeof(CarUserControl), new PropertyMetadata(null)); //Enter key down in the text box        public CarUserControl()        {            InitializeComponent();        }        public string StrValue        {            get { return (string)GetValue(StrValueProperty); }            set { SetValue(StrValueProperty, value); }        }        /// <summary>        /// "Enter" key down        /// </summary>        public ICommand KeyDownCommand        {            get { return (ICommand)GetValue(KeyDownCommandProperty); }            set { SetValue(KeyDownCommandProperty, value); }        }    }}

// ---型号 - car.cs

using System;using System.Collections.Generic;using System.ComponentModel;using System.Linq;using System.Text;using System.Threading.Tasks;namespace TestMVVM{    /// <summary>    /// A simple model    /// </summary>    class Car : INotifyPropertyChanged    {        public Car(string name) {            this.name = name;        }        private string name;        public event PropertyChangedEventHandler PropertyChanged;        public string Name        {            get { return name; }            set            {                name = value;                OnPropertyChanged("Name");            }        }        public void OnPropertyChanged(string name)        {            PropertyChangedEventHandler handler = PropertyChanged;            if (handler != null)            {                handler(this, new PropertyChangedEventArgs(name));            }        }    }}

-----主视图模型---

using System;using System.Collections.Generic;using System.Collections.ObjectModel;using System.ComponentModel;using System.Linq;using System.Text;using System.Threading.Tasks;using System.Windows.Input;namespace TestMVVM{    /// <summary>    /// The Main View Model    /// </summary>    class MainViewModel : INotifyPropertyChanged    {        /// <summary>        /// The main view model        /// </summary>        public MainViewModel()        {            //Create some test data            cars = new ObservableCollection<Car>();            cars.Add(new Car("Audi"));            cars.Add(new Car("Toyota"));            cars.Add(new Car("Subaru"));            cars.Add(new Car("Volvo"));        }        public event PropertyChangedEventHandler PropertyChanged;        private ObservableCollection<Car> cars; //List of tensioner spools        private ICommand enterDownCommand;        public ObservableCollection<Car> Cars        {            get { return cars; }            set            {                cars = value;                OnPropertyChanged("Cars");            }        }        public ICommand EnterDownCommand        {            get            {                if (enterDownCommand == null)                {                    enterDownCommand = new RelayMCommand<Car>(OnEnterDownCommand);                }                return enterDownCommand;            }        }        /// <summary>        /// Called when "Enter" key is down.         /// </summary>        /// <param name="obj"></param>        private void OnEnterDownCommand(Car obj)        {            //How do I get the text box value here?            Console.Write(">>"+obj.Name);        }        public void OnPropertyChanged(string name)        {            PropertyChangedEventHandler handler = PropertyChanged;            if (handler != null)            {                handler(this, new PropertyChangedEventArgs(name));            }        }    }}

----- Mainwindow ---

  <Window x:Class="TestMVVM.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:TestMVVM"        mc:Ignorable="d"        Title="MainWindow" Height="350" Width="525">    <Window.DataContext>        <local:MainViewModel x:Name ="MainVM"/>    </Window.DataContext>    <Grid>        <Grid.RowDefinitions>            <RowDefinition Height="*"/>            <RowDefinition Height="*"/>        </Grid.RowDefinitions>        <Grid Grid.Row="0">            <Viewbox>                <ItemsControl ItemsSource="{Binding Cars}" Margin="5" Width="200">                    <ItemsControl.ItemTemplate>                        <DataTemplate>                            <local:CarUserControl Margin="5"                                                  KeyDownCommand="{Binding Path=DataContext.EnterDownCommand, RelativeSource={RelativeSource AncestorType=ItemsControl}}"/>                        </DataTemplate>                    </ItemsControl.ItemTemplate>                    <ItemsControl.ItemsPanel>                        <ItemsPanelTemplate>                            <StackPanel Orientation="Vertical" IsItemsHost="True" />                        </ItemsPanelTemplate>                    </ItemsControl.ItemsPanel>                </ItemsControl>            </Viewbox>        </Grid>    </Grid></Window>

---继电器命令---

   using System;using System.Threading;using System.Windows.Input;namespace TestMVVM{    /// <summary>    /// Same as the Relay Command, except this handles an array of generic type <T>    /// </summary>    /// <typeparam name="T">Generic type parameter</typeparam>    public class RelayMCommand<T> : ICommand    {        private Predicate<T> _canExecute;        private Action<T> _execute;        public RelayMCommand(Action<T> execute, Predicate<T> canExecute = null)        {            _execute = execute;            _canExecute = canExecute;        }        private void Execute(T parameter)        {            _execute(parameter);        }        private bool CanExecute(T parameter)        {            return _canExecute == null ? true : _canExecute(parameter);        }        public bool CanExecute(object parameter)        {            return parameter == null ? false : CanExecute((T)parameter);        }        public void Execute(object parameter)        {            _execute((T)parameter);        }        public event EventHandler CanExecuteChanged;        public void RaiseCanExecuteChanged()        {            var temp = Volatile.Read(ref CanExecuteChanged);            if (temp != null)            {                temp(this, new EventArgs());            }        }    }}

看答案

<TextBox Text="{Binding Name}"             Grid.Column="1" Background="#FFE8D3D3" BorderThickness="0">    <TextBox.InputBindings>        <KeyBinding Key="Enter"                     Command="{Binding KeyDownCommand, ElementName=thisUC}"                     CommandParameter="{Binding}"/>    </TextBox.InputBindings></TextBox>