如何检测视图是否“肮脏”

您可以采用的一种方法是利用IChangeTracking和INotifyPropertyChanged接口。

如果你创建一个抽象基类，你的视图模型继承自(ViewModelBase)实现IChangeTracking和INotifyPropertyChanged接口，你可以有你的视图模型基附加到通知的属性更改(实际上表明视图模型已被修改)，这将设置IsChanged属性为真，以表明视图模型是"脏"。

使用这种方法，您将依赖于通过数据绑定的属性更改通知来跟踪更改，并在进行任何提交后重置更改跟踪。

在你描述的情况下，你可以处理Unloaded或Closing事件的视图来检查DataContext;如果DataContext实现了IChangeTracking，你可以使用IsChanged属性来确定是否有任何不可接受的更改。

简单的例子:

/// <summary>
/// Provides a base class for objects that support property change notification 
/// and querying for changes and resetting of the changed status.
/// </summary>
public abstract class ViewModelBase : IChangeTracking, INotifyPropertyChanged
{
    //========================================================
    //  Constructors
    //========================================================
    #region ViewModelBase()
    /// <summary>
    /// Initializes a new instance of the <see cref="ViewModelBase"/> class.
    /// </summary>
    protected ViewModelBase()
    {
        this.PropertyChanged += new PropertyChangedEventHandler(OnNotifiedOfPropertyChanged);
    }
    #endregion
    //========================================================
    //  Private Methods
    //========================================================
    #region OnNotifiedOfPropertyChanged(object sender, PropertyChangedEventArgs e)
    /// <summary>
    /// Handles the <see cref="INotifyPropertyChanged.PropertyChanged"/> event for this object.
    /// </summary>
    /// <param name="sender">The source of the event.</param>
    /// <param name="e">A <see cref="PropertyChangedEventArgs"/> that contains the event data.</param>
    private void OnNotifiedOfPropertyChanged(object sender, PropertyChangedEventArgs e)
    {
        if (e != null && !String.Equals(e.PropertyName, "IsChanged", StringComparison.Ordinal))
        {
            this.IsChanged = true;
        }
    }
    #endregion
    //========================================================
    //  IChangeTracking Implementation
    //========================================================
    #region IsChanged
    /// <summary>
    /// Gets the object's changed status.
    /// </summary>
    /// <value>
    /// <see langword="true"/> if the object’s content has changed since the last call to <see cref="AcceptChanges()"/>; otherwise, <see langword="false"/>. 
    /// The initial value is <see langword="false"/>.
    /// </value>
    public bool IsChanged
    {
        get
        {
            lock (_notifyingObjectIsChangedSyncRoot)
            {
                return _notifyingObjectIsChanged;
            }
        }
        protected set
        {
            lock (_notifyingObjectIsChangedSyncRoot)
            {
                if (!Boolean.Equals(_notifyingObjectIsChanged, value))
                {
                    _notifyingObjectIsChanged = value;
                    this.OnPropertyChanged("IsChanged");
                }
            }
        }
    }
    private bool _notifyingObjectIsChanged;
    private readonly object _notifyingObjectIsChangedSyncRoot = new Object();
    #endregion
    #region AcceptChanges()
    /// <summary>
    /// Resets the object’s state to unchanged by accepting the modifications.
    /// </summary>
    public void AcceptChanges()
    {
        this.IsChanged = false;
    }
    #endregion
    //========================================================
    //  INotifyPropertyChanged Implementation
    //========================================================
    #region PropertyChanged
    /// <summary>
    /// Occurs when a property value changes.
    /// </summary>
    public event PropertyChangedEventHandler PropertyChanged;
    #endregion
    #region OnPropertyChanged(PropertyChangedEventArgs e)
    /// <summary>
    /// Raises the <see cref="INotifyPropertyChanged.PropertyChanged"/> event.
    /// </summary>
    /// <param name="e">A <see cref="PropertyChangedEventArgs"/> that provides data for the event.</param>
    protected void OnPropertyChanged(PropertyChangedEventArgs e)
    {
        var handler = this.PropertyChanged;
        if (handler != null)
        {
            handler(this, e);
        }
    }
    #endregion
    #region OnPropertyChanged(string propertyName)
    /// <summary>
    /// Raises the <see cref="INotifyPropertyChanged.PropertyChanged"/> event for the specified <paramref name="propertyName"/>.
    /// </summary>
    /// <param name="propertyName">The <see cref="MemberInfo.Name"/> of the property whose value has changed.</param>
    protected void OnPropertyChanged(string propertyName)
    {
        this.OnPropertyChanged(new PropertyChangedEventArgs(propertyName));
    }
    #endregion
    #region OnPropertyChanged(params string[] propertyNames)
    /// <summary>
    /// Raises the <see cref="INotifyPropertyChanged.PropertyChanged"/> event for the specified <paramref name="propertyNames"/>.
    /// </summary>
    /// <param name="propertyNames">An <see cref="Array"/> of <see cref="String"/> objects that contains the names of the properties whose values have changed.</param>
    /// <exception cref="ArgumentNullException">The <paramref name="propertyNames"/> is a <see langword="null"/> reference (Nothing in Visual Basic).</exception>
    protected void OnPropertyChanged(params string[] propertyNames)
    {
        if (propertyNames == null)
        {
            throw new ArgumentNullException("propertyNames");
        }
        foreach (var propertyName in propertyNames)
        {
            this.OnPropertyChanged(propertyName);
        }
    }
    #endregion
}

在MVVM中，View被绑定到View-Model, View-Model又被绑定到Model。

视图不能是脏的，因为它的变化会立即反映到视图模型。

如果您希望更改仅在"OK"或"Accept"时应用于Model，
将视图绑定到不应用更改到模型的视图模型，
直到ApplyCommand或AcceptCommand(您定义和实现的)被执行。

(View绑定到的命令由View- model实现)

示例—VM:

public class MyVM : INotifyPropertyChanged
{
    public string MyText
    {
        get
        {
            return _MyText;
        }
        set
        {
            if (value == _MyText)
                return;
            _MyText = value;
            NotifyPropertyChanged("MyText");
        }
    }
    private string _MyText;
    public string MyTextTemp
    {
        get
        {
            return _MyTextTemp;
        }
        set
        {
            if (value == _MyTextTemp)
                return;
            _MyTextTemp = value;
            NotifyPropertyChanged("MyTextTemp");
            NotifyPropertyChanged("IsTextDirty");
        }
    }
    private string _MyTextTemp;
    public bool IsTextDirty
    {
        get
        {
            return MyText != MyTextTemp;
        }
    }
    public bool IsMyTextBeingEdited
    {
        get
        {
            return _IsMyTextBeingEdited;
        }
        set
        {
            if (value == _IsMyTextBeingEdited)
                return;
            _IsMyTextBeingEdited = value;
            if (!value)
            {
                MyText = MyTextTemp;
            }
            NotifyPropertyChanged("IsMyTextBeingEdited");
        }
    }
    private bool _IsMyTextBeingEdited;

    public event PropertyChangedEventHandler PropertyChanged;
    protected void NotifyPropertyChanged(string propertyName)
    {
        if (PropertyChanged != null)
            PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
    }
}

示例-视图:

    <Label Content="{Binding MyText}" />
    <!-- You can translate the events to commands by using a suitable framework -->
    <!-- or use code behind to update a new dependency property as in this example -->
    <TextBox
        LostFocus="TextBox_LostFocus"
        GotFocus="TextBox_GotFocus"
        Text="{Binding Path=MyTextTemp, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}"
        />

示例-视图-背后代码:

    public MainWindow()
    {
        InitializeComponent();
        SetBinding(IsTextBoxFocusedProperty,
            new Binding
            {
                Path = new PropertyPath("IsMyTextBeingEdited"),
                Mode = BindingMode.OneWayToSource,
            });
    }
    private void TextBox_LostFocus(object sender, RoutedEventArgs e)
    {
        IsTextBoxFocused = false;
    }
    private void TextBox_GotFocus(object sender, RoutedEventArgs e)
    {
        IsTextBoxFocused = true;
    }
    #region IsTextBoxFocused
    /// <summary>
    /// Gets or Sets IsTextBoxFocused
    /// </summary>
    public bool IsTextBoxFocused
    {
        get
        {
            return (bool)this.GetValue(IsTextBoxFocusedProperty);
        }
        set
        {
            this.SetValue(IsTextBoxFocusedProperty, value);
        }
    }
    /// <summary>
    /// The backing DependencyProperty behind IsTextBoxFocused
    /// </summary>
    public static readonly DependencyProperty IsTextBoxFocusedProperty = DependencyProperty.Register(
      "IsTextBoxFocused", typeof(bool), typeof(MainWindow), new PropertyMetadata(default(bool)));
    #endregion

创意:check entitystate:

问题是这指的是整个VIEW，所以当在任何编辑之前选择一个新的参与者(刷新表单)时，该值也是"Modified"。保存后，如果没有其他变化，我们也没有切换参与者，则值为"Unchanged"