WPF MVVM - 如何检测视图是否“脏" [英] WPF MVVM - How to detect if a View is "Dirty"

问题描述

如果视图上的任何字段已更改/更新，我目前需要通知我的应用程序用户.

I currently have a requirement to notify my application user if any fields have been changed/updated on a View.

例如，如果用户更改视图上的日期字段，然后尝试关闭视图，应用程序将显示一条消息，要求用户继续并丢失更改或取消，以便他们可以单击保存按钮.

For example, if the user changes a date field on the View and then tries to close the View, the application would display a message asking the user to Continue and lose changes or Cancel so that they can click the Save button.

问题是:如何检测视图中的任何数据字段已更改?

Problem is: How do I detect that any of the data fields changed in the View?

希望这是有道理的，而不是提前问候，

Hope this makes sense, than you in advance, regards,

推荐答案

您可以采取的一种方法是利用 IChangeTracking 和 INotifyPropertyChanged 接口.

One approach you can take is to leverage the IChangeTracking and INotifyPropertyChanged interfaces.

如果您创建一个抽象基类，您的视图模型继承自 (ViewModelBase)，它实现了 IChangeTracking 和 INotifyPropertyChanged 接口，您可以将您的视图模型基础附加到属性更改通知(实际上表明视图模型已被修改)，这将设置 IsChanged 属性为 true 表示视图模型是脏的".

If you create an abstract base class that your view models inherit from (ViewModelBase) which implements the IChangeTracking and INotifyPropertyChanged interfaces, you can have your view model base attach to notification of property changes (in effect signaling that the view model has been modified) and which will set the IsChanged property to true to indicate that the view model is 'dirty'.

使用这种方法，您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.

Using this approach, you are relying on property change notification via data binding to track changes and would reset the change tracking after any commits are made.

在您描述的情况下，您可以处理 Unloaded 或 Closing 事件以检查 DataContext;如果 DataContext 实现了 IChangeTracking，您可以使用 IsChanged 属性来确定是否进行了任何未接受的更改.

In the case you described you could handle the Unloaded or Closing event of your view to inspect the DataContext; and if the DataContext implements IChangeTracking you can use the IsChanged property to determine if any unaccepted changes have been made.

简单示例:

/// <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
}

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