c# – 对于WPF 4.5 DataGrids,INotifyDataErrorInfo是否已损坏
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我在WPF 4.5项目中做了一个简单的INotifyDataErrorInfo实现.这是WPF的新界面,但已在Silverlight中使用了一段时间.
我知道NET4.5仍然被认为是alpha,但我正在尝试解决它是我的代码还是错误的框架.
接口按预期工作,但在将对象绑定到DataGrid时失败.
我收到的例外是：
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http://dl.dropbox.com/u/14740106/INotifyDataErrorInfoTest.zip以下或项目中
如果共识是这是一个错误,那么我将发布到MS Connect.
测试：
有两个文本框绑定到Person对象的单个实例.将第一个文本框设置为具有值的James,它将无法通过验证并显示红色框.如果将网格中任何用户的名字设置为James,则会抛出异常.
PS：我知道它不是MVVM,但它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>
解决方法:
答案是肯定的.我打开了一个ticket with Microsoft,他们已经确认代码很好,这是.NET 4.5 DataGrid的一个错误.
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.
非常大的bug必须等到最终版本.我们希望它能在下一个版本中得到解决.
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