WPF DataGrid 验证/绑定模式错误

Question

我创建了一个非常简单的新项目，仅测试 Microsoft WPF DataGrid 行为。不涉及其他，我只使用标准的DataGrid：

<Window x:Class="MainWindow"
         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" 
         mc:Ignorable="d" 
         d:DesignHeight="300" d:DesignWidth="300">

    <DataGrid ItemsSource="{Binding Employees, Mode=TwoWay}"
              x:Name="tlv"
              AutoGenerateColumns="False"
              SelectionMode="Extended"
              CanUserAddRows="true"
              SelectionUnit="CellOrRowHeader">
        <DataGrid.Columns>
            <DataGridTextColumn Header="First Name" Binding="{Binding FirstName, Mode=TwoWay}"/>
            <DataGridTextColumn Header="Last Name" Binding="{Binding LastName, Mode=TwoWay}"/>
            <DataGridTextColumn Header="Salary" Binding="{Binding Salary, Mode=TwoWay, ValidatesOnDataErrors=True, UpdateSourceTrigger=LostFocus}"/>
        </DataGrid.Columns>
    </DataGrid>
</Window>

后面的代码：

Imports System.Collections.ObjectModel
Imports DataGridTest.Data

Class MainWindow
Sub New()

    ' This call is required by the designer.
    InitializeComponent()

    ' Add any initialization after the InitializeComponent() call.
    Me.DataContext = Me
    Employees = New ObservableCollection(Of Employee)(EmployeeRepository.GetFlatListData())
    BindableSelectedItems = New ObservableCollection(Of Object)
End Sub


Private _employees As ObservableCollection(Of Employee)

Public Property Employees() As ObservableCollection(Of Employee)
    Get
        Return _employees
    End Get
    Set(ByVal value As ObservableCollection(Of Employee))
        _employees = value
    End Set
End Property


Private _bindableSelectedItems As ObservableCollection(Of Object)
Public Property BindableSelectedItems() As ObservableCollection(Of Object)
    Get
        Return _bindableSelectedItems
    End Get
    Set(value As ObservableCollection(Of Object))
        'Set the new value of BindableSelectedItems
        _bindableSelectedItems = value
    End Set
End Property


Private _selectedEmployeeForSelectedItemsSimulation As Employee
Public Property SelectedEmployeeForSelectedItemsSimulation() As Employee
    Get
        Return _selectedEmployeeForSelectedItemsSimulation
    End Get
    Set(value As Employee)
        'Set the new value of SelectedEmployeeForSelectedItemsSimulation
        _selectedEmployeeForSelectedItemsSimulation = value

        If _selectedEmployeeForSelectedItemsSimulation IsNot Nothing AndAlso BindableSelectedItems IsNot Nothing Then
            BindableSelectedItems.Clear()
            BindableSelectedItems.Add(value)
        End If
    End Set
End Property
End Class

Employee 类，它实现了 IDataErrorInfo：

Imports Microsoft.Practices.Prism.ViewModel
Imports System.Collections.ObjectModel
Imports System.ComponentModel

Namespace Data
Public Class Employee
    Inherits NotificationObject
    Implements IDataErrorInfo

    Public Sub New()

    End Sub

    Public Sub New(ByVal fName As String, ByVal lName As String, ByVal salary As Double)
        FirstName = fName
        LastName = lName
        Me.Salary = salary
    End Sub


    Private _firstName As String
    Public Property FirstName() As String
        Get
            Return _firstName
        End Get
        Set(value As String)
            'Set the new value of FirstName
            _firstName = value

            'Warn any Observers that the FirstName have changed.
            RaisePropertyChanged(Function() Me.FirstName)
        End Set
    End Property


    Private _lastName As String
    Public Property LastName() As String
        Get
            Return _lastName
        End Get
        Set(value As String)
            'Set the new value of LastName
            _lastName = value

            'Warn any Observers that the LastName have changed.
            RaisePropertyChanged(Function() Me.LastName)
        End Set
    End Property


    Private _isSelected As Boolean
    Public Property IsSelected() As Boolean
        Get
            Return _isSelected
        End Get
        Set(value As Boolean)
            'Set the new value of IsSelected
            _isSelected = value

            'Warn any Observers that the IsSelected have changed.
            RaisePropertyChanged(Function() Me.IsSelected)
        End Set
    End Property

    Private _salary As Double
    Public Property Salary() As Double
        Get
            Return _salary
        End Get
        Set(value As Double)
            'Set the new value of Salary
            _salary = value

            'Warn any Observers that the Salary have changed.
            RaisePropertyChanged(Function() Me.Salary)
        End Set
    End Property



    Public ReadOnly Property [Error] As String Implements IDataErrorInfo.Error
        Get
            Return String.Empty
        End Get
    End Property

    Default Public ReadOnly Property Item(columnName As String) As String Implements IDataErrorInfo.Item
        Get

            If Me.Salary <= 0 Then
                Return "The salary must be positive."
            End If

            Return String.Empty
        End Get
    End Property
End Class
End Namespace

到目前为止，一切都很好。然后，当我在添加新行后尝试更新工资值时会发生以下情况：

值重置为0！

1. 为什么要这样做？我使用 DataGrid 的方式有问题吗？
2. 有解决方法吗？

[编辑] ...和解决方法

我终于找到了一种解决方法，即使我仍然不知道我现在认为是 Microsoft DataGrid 中的错误的原因。

如果在数据网格列中指定了绑定模式带有验证，会出现错误； 如果改为我不指定绑定模式，一切都很好。

<DataGridTextColumn Header="Salary" Binding="{Binding Salary, ValidatesOnDataErrors=True, UpdateSourceTrigger=LostFocus}"/>

不过，我不太明白的是，据我所知，默认绑定模式是 TwoWay... 好吧，至少我解决了我的问题。

我在 Microsoft Connect 上打开了一个错误报告，here

Answer 1

只是让你知道，我从 Microsoft 那里得到消息，他们说这不重要，他们甚至不会尝试解决错误。

看看here

所以，这是一个已经存在一段时间的错误，并且不会很快修复。

Answer 2

假设 DataGrid 已绑定，我之前使用 CellEditEnding 事件创建了一个解决方案（尽管不使用反射，只是一个实现 INotifyPropertyChanged 的​​类）。要使其正常工作，需要将 UpdateSourceTrigger 设置为列绑定的显式

因此，例如，假设您的数据网格的 itemssource 绑定到一个 observablecollection(of Shape)。每个形状都有两个属性 ShapeName 和 NumberOfSides。为确保用户不会输入 0 或更少的边数

（大概）

Public Class Shape
    Implements ComponentModel.INotifyPropertyChanged

    Dim _ShapeName As String
    Dim _NumberOfSides As Int32

    Public Property ShapeName As String
        Get
            Return _ShapeName
        End Get
        Set(value As String)
            _ShapeName = value
            Me.DataStateChanged("ShapeName")
        End Set
    End Property

    Public Property NumberOfSides As Int32
        Get
            Return _NumberOfSides
        End Get
        Set(value As Int32)
            If value > 0 Then
                _NumberOfSides = value
            End If
            Me.DataStateChanged("NumberOfSides")
        End Set
    End Property


#Region "INotifyPropertyChanged Members"

    Public Event PropertyChanged(ByVal sender As Object, ByVal e As ComponentModel.PropertyChangedEventArgs) _
        Implements _
            ComponentModel.INotifyPropertyChanged.PropertyChanged

    Protected Sub DataStateChanged(ByVal propertyName As String)
        ' Raise the event
        If Not String.IsNullOrEmpty(propertyName) Then
            RaiseEvent PropertyChanged(Me, _
            New ComponentModel.PropertyChangedEventArgs(propertyName))
        End If
    End Sub
#End Region

End Class

然后在数据网格内

private sub me_CellEditEnding(sender As System.Object, e As System.Windows.Controls.DataGridCellEditEndingEventArgs) Handles me.CellEditEnding
            If e.EditAction = DataGridEditAction.Commit Then

                    Dim EditedItem As Shape = CType(e.Row.Item, Shape)
                    Dim ValueBefore As int32 = EditedItem.NumberOfSides 

                    For Each currentExpression As BindingExpressionBase In e.EditingElement.BindingGroup.BindingExpressions
                       'the value is changed or not by the update within the property
                        currentExpression.UpdateSource()
                    Next


                    If ValueBefore = EditedItem.NumberOfSides then
                        'The value update was unsuccessful

                    End If
                End If
    End Sub