WPF Parent Element Lost Focus - wpf

Question

I am developing a WPF application. In one of my pages I have a DockPanel with 3 ComboBoxes within it. These 3 ComboBoxes are dependent on each other. So, I have a binding group on the DockPanel and a validation rule for that binding group.
I would like to validate these 3 ComboBoxes when the DockPanel loses focus; however, the DockPanel's LostFocus event is fired when the user clicks on one of the child ComboBoxes within it!
I would have thought that if the child control has focus, the parent control would also have focus...however this does not seem to be the case.
I am looking for a solution to perform validation on the binding group when the DockPanel loses focus...where the focus is lost to a control that is not one of its children.
Edit:
So, I created as simple an application as I could to demonstrate the problem.
I have a "FertilizerCombination" class that contains 3 integers that make up the Fertilizer. These must be unique within the application. Currently the only combination that is not available is 10-10-10. This is a hard coded value in the class.
Public Class FertilizerCombination
Private _nitrogen As Integer
Private _phosphorous As Integer
Private _potassium As Integer
<System.ComponentModel.DataAnnotations.Range(1, 20)> _
Public Property Nitrogen As Integer
Get
Return _nitrogen
End Get
Set(value As Integer)
System.ComponentModel.DataAnnotations.Validator.ValidateProperty(value, NitrogenValidationContext)
_nitrogen = value
End Set
End Property
<System.ComponentModel.DataAnnotations.Range(1, 20)> _
Public Property Phosphorous As Integer
Get
Return _phosphorous
End Get
Set(value As Integer)
System.ComponentModel.DataAnnotations.Validator.ValidateProperty(value, PhosphorousValidationContext)
_phosphorous = value
End Set
End Property
<System.ComponentModel.DataAnnotations.Range(1, 20)> _
Public Property Potassium As Integer
Get
Return _potassium
End Get
Set(value As Integer)
System.ComponentModel.DataAnnotations.Validator.ValidateProperty(value, PotassiumValidationContext)
_potassium = value
End Set
End Property
Public Sub New()
End Sub
Public Sub New(ByVal nitrogen As Integer, ByVal phosphorous As Integer, ByVal potassium As Integer)
Me.Nitrogen = nitrogen
Me.Phosphorous = phosphorous
Me.Potassium = potassium
End Sub
Public Shared Function FertilizerCombinationAvailable(ByVal nitrogen As Integer, ByVal phosphorous As Integer, ByVal potassium As Integer) As Boolean
'Checking against combinations already used'
If nitrogen = "10" And phosphorous = "10" And potassium = "10" Then
'Combination has already been used'
Return False
End If
'Combination was not used yet'
Return True
End Function
Public Sub SetFertilizerCombination(ByVal nitrogen As Integer, ByVal phosphorous As Integer, ByVal potassium As Integer)
System.ComponentModel.DataAnnotations.Validator.ValidateProperty(nitrogen, NitrogenValidationContext)
System.ComponentModel.DataAnnotations.Validator.ValidateProperty(phosphorous, PhosphorousValidationContext)
System.ComponentModel.DataAnnotations.Validator.ValidateProperty(potassium, PotassiumValidationContext)
If FertilizerCombination.FertilizerCombinationAvailable(nitrogen, phosphorous, potassium) = False Then
Throw New ArgumentException("This fertilizer combination has already been used")
End If
Me.Nitrogen = nitrogen
Me.Phosphorous = phosphorous
Me.Potassium = potassium
End Sub
Private NitrogenValidationContext = New System.ComponentModel.DataAnnotations.ValidationContext(Me, Nothing, Nothing) With {.MemberName = "Nitrogen"}
Private PhosphorousValidationContext = New System.ComponentModel.DataAnnotations.ValidationContext(Me, Nothing, Nothing) With {.MemberName = "Phosphorous"}
Private PotassiumValidationContext = New System.ComponentModel.DataAnnotations.ValidationContext(Me, Nothing, Nothing) With {.MemberName = "Potassium"}
End Class
I have a created a Validation Rule for the Fertilizer Combination Class:
Public Class FertilizerCombinationValidationRule
Inherits ValidationRule
Public Overrides Function Validate(ByVal value As Object, ByVal cultureInfo As System.Globalization.CultureInfo) As System.Windows.Controls.ValidationResult
Dim bg As BindingGroup = TryCast(value, BindingGroup)
If bg IsNot Nothing AndAlso bg.Items.Count > 0 Then
'The BindingGroup Items property contains the original object(s)'
Dim fertilizerCombo As FertilizerCombination = TryCast(bg.Items(0), FertilizerCombination)
'Using the BindingGroups GetValue method to retrieve the user provided values'
Dim proposedNitrogen As Integer
Dim proposedPhosphorous As Integer
Dim proposedPotassium As Integer
Try
proposedNitrogen = bg.GetValue(fertilizerCombo, "Nitrogen")
proposedPhosphorous = bg.GetValue(fertilizerCombo, "Phosphorous")
proposedPotassium = bg.GetValue(fertilizerCombo, "Potassium")
If FertilizerCombination.FertilizerCombinationAvailable(proposedNitrogen, proposedPhosphorous, proposedPotassium) = False Then
Return New ValidationResult(False, "This fertializer combination has already been used")
End If
Catch noValue As System.Windows.Data.ValueUnavailableException
'a binding was not properly bound yet'
End Try
End If
Return New ValidationResult(True, Nothing)
End Function
End Class
I have a "PlantSolution" class that has a FertilizerCombination property. I also have a VM for that class so that it's easy for binding in the XAML:
Public Class PlantSolutionVM
Public Property PlantSolution As PlantSolution
Public Sub New()
PlantSolution = New PlantSolution("Produce Blooms", "Using this fertilizer will help your plant produce flowers!", 10, 10, 20)
End Sub
End Class
Public Class PlantSolution
Private _name As String
Private _description As String
Private _fertilizer As FertilizerCombination
<System.ComponentModel.DataAnnotations.Required()>
Public Property Name As String
Get
Return _name
End Get
Set(value As String)
System.ComponentModel.DataAnnotations.Validator.ValidateProperty(value, NameValidationContext)
_name = value
End Set
End Property
<System.ComponentModel.DataAnnotations.Required()>
Public Property Description As String
Get
Return _description
End Get
Set(value As String)
System.ComponentModel.DataAnnotations.Validator.ValidateProperty(value, DescriptionValidationContext)
_description = value
End Set
End Property
Public ReadOnly Property Fertilizer As FertilizerCombination
Get
Return _fertilizer
End Get
End Property
Public Sub New(name As String, description As String, nitrogen As Integer, phosphorous As Integer, potassium As Integer)
_fertilizer = New FertilizerCombination(nitrogen, phosphorous, potassium)
Me.Name = name
Me.Description = description
End Sub
Private NameValidationContext = New System.ComponentModel.DataAnnotations.ValidationContext(Me, Nothing, Nothing) With {.MemberName = "Name"}
Private DescriptionValidationContext = New System.ComponentModel.DataAnnotations.ValidationContext(Me, Nothing, Nothing) With {.MemberName = "Description"}
End Class
Now here is my XAML for a window called "FunWithFocus":
<Grid>
<Grid.Resources>
<x:Array x:Key="CombinationOptions" Type="sys:Int32" xmlns:sys="clr-namespace:System;assembly=mscorlib">
<sys:Int32>0</sys:Int32>
<sys:Int32>1</sys:Int32>
<sys:Int32>2</sys:Int32>
<sys:Int32>3</sys:Int32>
<sys:Int32>4</sys:Int32>
<sys:Int32>5</sys:Int32>
<sys:Int32>6</sys:Int32>
<sys:Int32>7</sys:Int32>
<sys:Int32>8</sys:Int32>
<sys:Int32>9</sys:Int32>
<sys:Int32>10</sys:Int32>
<sys:Int32>11</sys:Int32>
<sys:Int32>12</sys:Int32>
<sys:Int32>13</sys:Int32>
<sys:Int32>14</sys:Int32>
<sys:Int32>15</sys:Int32>
<sys:Int32>16</sys:Int32>
<sys:Int32>17</sys:Int32>
<sys:Int32>18</sys:Int32>
<sys:Int32>19</sys:Int32>
<sys:Int32>20</sys:Int32>
</x:Array>
<local:PlantSolutionVM x:Key="PlantSolutionVM" />
<Style TargetType="DockPanel">
<Style.Triggers>
<Trigger Property="Validation.HasError" Value="true">
<Setter Property="ToolTip" Value="{Binding RelativeSource={x:Static RelativeSource.Self}, Path=(Validation.Errors)[0].ErrorContent}"/>
</Trigger>
</Style.Triggers>
</Style>
<Style TargetType="TextBox">
<Style.Triggers>
<Trigger Property="Validation.HasError" Value="true">
<Setter Property="ToolTip" Value="{Binding RelativeSource={x:Static RelativeSource.Self}, Path=(Validation.Errors)[0].ErrorContent}"/>
</Trigger>
</Style.Triggers>
</Style>
</Grid.Resources>
<Grid DataContext="{Binding Source={StaticResource PlantSolutionVM}, Path=PlantSolution}" Margin="50">
<Grid.RowDefinitions>
<RowDefinition Height="Auto" />
<RowDefinition Height="*"/>
<RowDefinition Height="*"/>
<RowDefinition Height="Auto" />
</Grid.RowDefinitions>
<Grid.ColumnDefinitions>
<ColumnDefinition Width="Auto"/>
<ColumnDefinition Width="*"/>
</Grid.ColumnDefinitions>
<TextBlock Text="Solution Name:" Grid.Row="0" Grid.Column="0" Margin="5"/>
<TextBox x:Name="ItemName" Text="{Binding Name, ValidatesOnDataErrors=True, ValidatesOnExceptions=True}" Grid.Row="0" Grid.Column="1" VerticalAlignment="Top" Margin="5"/>
<TextBlock Text="Description of Problem:" Grid.Row="1" Grid.Column="0" Margin="5"/>
<TextBox x:Name="ItemDescription" Text="{Binding Description, ValidatesOnDataErrors=True, ValidatesOnExceptions=True}" Grid.Row="1" Grid.Column="1" Margin="5"/>
<TextBlock Text="Recommended Fertilizer:" Grid.Row="2" Grid.Column="0" Margin="5"/>
<DockPanel x:Name="FertilizerCombinationContainer" DataContext="{Binding Fertilizer}" Grid.Row="2" Grid.Column="1" Margin="5" HorizontalAlignment="Left" VerticalAlignment="Top">
<DockPanel.BindingGroup>
<BindingGroup NotifyOnValidationError="True">
<BindingGroup.ValidationRules>
<local:FertilizerCombinationValidationRule />
</BindingGroup.ValidationRules>
</BindingGroup>
</DockPanel.BindingGroup>
<ComboBox x:Name="NitrogenValue" HorizontalAlignment="Left" VerticalAlignment="Top"
ItemsSource="{StaticResource CombinationOptions}"
SelectedItem="{Binding Nitrogen}"/>
<ComboBox x:Name="PhosphorousValue" HorizontalAlignment="Left" VerticalAlignment="Top"
ItemsSource="{StaticResource CombinationOptions}"
SelectedItem="{Binding Phosphorous}"/>
<ComboBox x:Name="PotatssiumValue" HorizontalAlignment="Left" VerticalAlignment="Top"
ItemsSource="{StaticResource CombinationOptions}"
SelectedItem="{Binding Potassium}"/>
</DockPanel>
<Button x:Name="SaveIt" Content="Save" Grid.Row="3" Grid.Column="1"/>
</Grid>
</Grid>
And here is the Code Behind for the page:
Class FunWithFocus
Private Sub FertilizerCombinationContainer_Loaded(sender As Object, e As System.Windows.RoutedEventArgs) Handles FertilizerCombinationContainer.Loaded
'FertilizerCombinationContainer.BindingGroup.CancelEdit()'
'FertilizerCombinationContainer.BindingGroup.BeginEdit()'
End Sub
Private Sub FertilizerCombinationContainer_LostFocus(sender As Object, e As System.Windows.RoutedEventArgs) Handles FertilizerCombinationContainer.LostFocus
'This will get fired if the user drops down one of the comboboxes'
End Sub
'This is how I am currently handling the lost focus...but it doesn't fire if the user clicks somewhere that doesn't take keyboard focus'
'Private Sub FertilizerCombinationContainer_IsKeyboardFocusWithinChanged(sender As Object, e As System.Windows.DependencyPropertyChangedEventArgs) Handles FertilizerCombinationContainer.IsKeyboardFocusWithinChanged'
' If FertilizerCombinationContainer.IsKeyboardFocusWithin = False Then'
' FertilizerCombinationContainer.BindingGroup.ValidateWithoutUpdate()'
' If Validation.GetErrors(FertilizerCombinationContainer).Count = 0 Then'
' FertilizerCombinationContainer.BindingGroup.CommitEdit()'
' Dim bg As BindingGroup = FertilizerCombinationContainer.BindingGroup'
' Dim fertilizerCombo As FertilizerCombination = bg.Items(0)'
' Dim proposedNitrogen As Integer'
' Dim proposedPhosphorous As Integer'
' Dim proposedPotassium As Integer'
' Try'
' proposedNitrogen = bg.GetValue(fertilizerCombo, "Nitrogen")'
' proposedPhosphorous = bg.GetValue(fertilizerCombo, "Phosphorous")'
' proposedPotassium = bg.GetValue(fertilizerCombo, "Potassium")'
' ''there was a change: set it'
' fertilizerCombo.SetFertilizerCombination(proposedNitrogen, proposedPhosphorous, proposedPotassium)'
' Catch noValue As System.Windows.Data.ValueUnavailableException'
' ''a binding was not properly bound yet'
' End Try'
' End If'
' End If'
'End Sub'
End Class
If you put a break point on the method that handles FertilizerCombinationContainer's LostFocus event, you will notice that it is fired when you select one of the ComboBoxes even though it is a child of the FertilizerContainer element.
Thank you,
-Frinny