c# - WPF 4.5 DataGrids 的 INotifyDataErrorInfo 是否损坏

Question

我在 WPF 4.5 项目中简单实现了 INotifyDataErrorInfo。这是 WPF 的新界面，但在 Silverlight 中已经可用了一段时间。

我知道 NET4.5 仍被认为是 alpha，但我正在尝试确定是我的代码还是框架有问题。

界面按预期工作，但当对象绑定(bind)到 DataGrid 时失败。

我收到的异常是:

System.NullReferenceException was unhandled by user code
Message=Object reference not set to an instance of an object.
Source=PresentationFramework StackTrace: at MS.Internal.Data.ClrBindingWorker.OnDataErrorsChanged(INotifyDataErrorInfo indei, String propName) at MS.Internal.Data.PropertyPathWorker.OnErrorsChanged(Object sender, DataErrorsChangedEventArgs e) at System.Windows.WeakEventManager.ListenerList`1.DeliverEvent(Object sender, EventArgs e, Type managerType) at System.Windows.WeakEventManager.DeliverEvent(Object sender, EventArgs args) at System.ComponentModel.ErrorsChangedEventManager.OnErrorsChanged(Object sender, DataErrorsChangedEventArgs args) at INotifyDataErrorInfoTest.Person.NotifyErrorsChanged(String property) in INotifyDataErrorInfoTest\Person.cs:line 109 at INotifyDataErrorInfoTest.Person.AddErrorForProperty(String property, String error) in INotifyDataErrorInfoTest\Person.cs:line 122 at INotifyDataErrorInfoTest.Person.Validate(String propertyName) in INotifyDataErrorInfoTest\Person.cs:line 150 at INotifyDataErrorInfoTest.Person.set_FirstName(String value) in INotifyDataErrorInfoTest\Person.cs:line 18

代码在下面或项目中 http://dl.dropbox.com/u/14740106/INotifyDataErrorInfoTest.zip

如果一致认为这是一个错误，那么我将发布到 MS Connect。

测试:有两个文本框绑定(bind)到 Person 对象的单个实例。将第一个文本框设置为 James 的值，它将验证失败并显示红色框。如果您将网格中任何用户的名字设置为 James，则会抛出异常。

PS:我知道这不是MVVM，但只是为了证明或反驳问题。

 public class Person : INotifyDataErrorInfo, INotifyPropertyChanged
    {
        string _firstName;
        public string FirstName
        {
            get { return _firstName; }
            set
            {
                _firstName = value;
                Validate("FirstName");
                OnPropertyChanged("FirstName");
            }
        }

        string _lastName;
        public string LastName
        {
            get { return _lastName; }
            set
            {
                _lastName = value;
                Validate("LastName");
                OnPropertyChanged("LastName");
            }
        }

        public Person()
        {
        }

        public Person(string first, string last)
        {
            this._firstName = first;
            this._lastName = last;
        }

        #region INotifyPropertyChanged Members

        /// <summary>
        /// Event to indicate that a property has changed.
        /// </summary>
        [field: NonSerialized]
        public event PropertyChangedEventHandler PropertyChanged;

        /// <summary>
        /// Called when a property is changed
        /// </summary>
        /// <param name="propertyName">The name of the property that has changed.</param>
        protected virtual void OnPropertyChanged(string propertyName)
        {
            OnPropertyChanged(new PropertyChangedEventArgs(propertyName));
        }

        /// <summary>
        /// Called when a property is changed
        /// </summary>
        /// <param name="e">PropertyChangedEventArgs</param>
        protected virtual void OnPropertyChanged(PropertyChangedEventArgs e)
        {

            //Validate the property
            Validate(e.PropertyName);

            if (null != PropertyChanged)
            {
                PropertyChanged(this, e);
            }

        }

        #endregion

        #region INotifyDataErrorInfo Members

        public event EventHandler<DataErrorsChangedEventArgs> ErrorsChanged;
        private Dictionary<string, List<string>> _errors = new Dictionary<string, List<string>>();

        public IEnumerable GetErrors(string propertyName)
        {
            if (string.IsNullOrEmpty(propertyName))
            {
                return (_errors.Values);
            }

            MakeOrCreatePropertyErrorList(propertyName);
            return _errors[propertyName];
        }

        public bool HasErrors
        {
            get
            {
                return (_errors.Where(c => c.Value.Count > 0).Count() > 0);
            }
        }

        void NotifyErrorsChanged(string property)
        {
            if (ErrorsChanged != null)
            {
                ErrorsChanged(this, new DataErrorsChangedEventArgs(property));
            }
        }
        public void ClearErrorFromProperty(string property)
        {
            MakeOrCreatePropertyErrorList(property);
            _errors[property].Clear();
            NotifyErrorsChanged(property);
        }
        public void AddErrorForProperty(string property, string error)
        {
            MakeOrCreatePropertyErrorList(property);
            _errors[property].Add(error);
            NotifyErrorsChanged(property);
        }

        void MakeOrCreatePropertyErrorList(string propertyName)
        {
            if (!_errors.ContainsKey(propertyName))
            {
                _errors[propertyName] = new List<string>();
            }
        }

        #endregion

        /// <summary>
        /// Force the object to validate itself using the assigned business rules.
        /// </summary>
        /// <param name="propertyName">Name of the property to validate.</param>
        public void Validate(string propertyName)
        {
            if (string.IsNullOrEmpty(propertyName))
            {
                return;
            }

            if (propertyName == "FirstName")
            {
                if (FirstName == "James")
                {
                    AddErrorForProperty(propertyName, "FirstName can't be James");
                }
                else
                {
                    ClearErrorFromProperty(propertyName);
                }
            }
        }
    }

public class NameList : ObservableCollection<Person>
    {
        public NameList()
            : base()
        {
            Add(new Person("Willa", "Cather"));
            Add(new Person("Isak", "Dinesen"));
            Add(new Person("Victor", "Hugo"));
            Add(new Person("Jules", "Verne"));
        }
    }

   public partial class MainWindow : Window
    {

        Person _person = new Person();

        public MainWindow()
        {
            InitializeComponent();
            DataContext = this;
        }

        public Person Person
        {
            get { return _person; }
        }
}

<Window x:Class="INotifyDataErrorInfoTest.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:c="clr-namespace:INotifyDataErrorInfoTest"
        Title="MainWindow" Height="350" Width="525">

    <Window.Resources>
        <c:NameList x:Key="NameListData"/>
    </Window.Resources>
    <StackPanel>
        <StackPanel.Resources>
            <Style TargetType="TextBox">
                <Setter Property="Margin" Value="5"></Setter>
            </Style>
        </StackPanel.Resources>
        <TextBox Text="{Binding Person.FirstName, Mode=TwoWay, ValidatesOnNotifyDataErrors=True}"/>
        <TextBox Text="{Binding Person.LastName, Mode=TwoWay, ValidatesOnNotifyDataErrors=True}"/>
        <TextBlock>To generate an error, set the FirstName of any row to James.
        </TextBlock>
        <DataGrid ItemsSource="{Binding Source={StaticResource NameListData}}" AutoGenerateColumns="True"></DataGrid>
    </StackPanel>
</Window>

Answer 1

答案是肯定的。我开了一个ticket with Microsoft他们已经确认代码没有问题，但它是 .NET 4.5 DataGrid 的错误。

This is our bug, not yours. When you edit a DataGrid cell, the DataGrid discards bindings for the "display" template and replaces them with bindings for the "edit" template. The discarded bindings should stop listening to the INDEI.ErrorsChanged event. They don't (that's the bug), but they are not prepared to get the event any more. When the event arrives, a null-reference crash occurs.

This will be fixed in the final release. Thanks for finding and reporting it.

相当大的错误必须等到最终版本。我们希望它在下一个版本中得到修复。