DataGridTextColumn.MaxLength?

Question

Come si imposta la proprietà MaxLength di DataGridTextColumn?

Answer 1

<tk:DataGridTextColumn Binding="{Binding Text}"> 
    <tk:DataGridTextColumn.EditingElementStyle> 
     <Style TargetType="TextBox"> 
      <Setter Property="MaxLength" Value="16"/> 
     </Style> 
    </tk:DataGridTextColumn.EditingElementStyle> 
</tk:DataGridTextColumn> 

Si potrebbe anche impostarlo utilizzando il seguente comportamento in modo da non dover usare uno stile e setter ogni volta:

Public Class TextBoxBehavior 
    Private Shared Types As Type() = New Type() {GetType(AutoCompleteBox), GetType(ComboBox), GetType(DataGridTextColumn)} 

    Public Shared Function GetMaxLength(ByVal element As DependencyObject) As Integer 
     Return element.GetValue(MaxLengthProperty) 
    End Function 

    Public Shared Sub SetMaxLength(ByVal element As DependencyObject, ByVal value As Integer) 
     element.SetValue(MaxLengthProperty, value) 
    End Sub 

    Private Shared Sub ValidateElement(ByVal element As DependencyObject) 
     If element Is Nothing Then Throw New ArgumentNullException("element") 
     If Not Types.Contains(element.GetType) Then Throw New NotSupportedException("The TextBoxBehavior is not supported for the given element") 
    End Sub 

    Public Shared ReadOnly MaxLengthProperty As DependencyProperty = 
    DependencyProperty.RegisterAttached("MaxLength", 
         GetType(Integer), GetType(TextBoxBehavior), 
         New FrameworkPropertyMetadata(Integer.MaxValue, AddressOf TextBox_MaxLengthChanged)) 

    Private Shared Sub TextBox_MaxLengthChanged(ByVal sender As Object, ByVal e As DependencyPropertyChangedEventArgs) 
     If sender Is Nothing Then Exit Sub 

     Dim value = DirectCast(e.NewValue, Integer) 

     If TypeOf sender Is AutoCompleteBox Then 
      Dim acb = DirectCast(sender, AutoCompleteBox) 

      If acb.IsLoaded Then 
       Dim tb = DirectCast(acb.Template.FindName("Text", acb), TextBox) 
       tb.MaxLength = value 
      Else 
       acb.AddHandler(AutoCompleteBox.LoadedEvent, New RoutedEventHandler(AddressOf Element_Loaded)) 
      End If 
     ElseIf TypeOf sender Is ComboBox Then 
      Dim cb = DirectCast(sender, ComboBox) 
      If cb.IsLoaded Then 
       Dim tb = DirectCast(cb.Template.FindName("PART_EditableTextBox", cb), TextBox) 
       tb.MaxLength = value 
      Else 
       cb.AddHandler(ComboBox.LoadedEvent, New RoutedEventHandler(AddressOf Element_Loaded)) 
      End If 
     ElseIf TypeOf sender Is DataGridTextColumn Then 
      Dim dgtc = DirectCast(sender, DataGridTextColumn) 

      Dim setter = GetIsMaxLengthSet(dgtc.EditingElementStyle) 
      If setter Is Nothing Then 
       Dim style = New Style(GetType(TextBox), dgtc.EditingElementStyle) 
       style.Setters.Add(New Setter(TextBox.MaxLengthProperty, value)) 
       dgtc.EditingElementStyle = style 
       style.Seal() 
      Else 
       setter.Value = value 
      End If 
     End If 
    End Sub 

    Private Shared Function GetIsMaxLengthSet(ByVal style As Style) As Setter 
     If style Is Nothing Then Return Nothing 
     Dim setter = style.Setters.LastOrDefault(Function(s) TypeOf s Is Setter AndAlso DirectCast(s, Setter).Property Is TextBox.MaxLengthProperty) 
     If setter IsNot Nothing Then Return setter Else Return GetIsMaxLengthSet(style.BasedOn) 
    End Function 

    Private Shared Sub Element_Loaded(ByVal sender As Object, ByVal e As RoutedEventArgs) 
     Dim ml = GetMaxLength(sender) 
     TextBox_MaxLengthChanged(sender, New DependencyPropertyChangedEventArgs(TextBox.MaxLengthProperty, -1, ml)) 
     sender.RemoveHandler(FrameworkElement.LoadedEvent, New RoutedEventHandler(AddressOf Element_Loaded)) 
    End Sub 
End Class 

Usage:

<ComboBox xmlns:loc="MyNamesapace" loc:TextBoxBehavior.MaxLength="50" /> 

Answer 2

Se si dispone di uno stile condiviso tra tutte le colonne e si desidera aggiungere uno stile aggiuntivo a uno o più di questi, è possibile utilizzare la proprietà Style.BasedOn:

<DataGridTextColumn Binding="{Binding SomeProperty, UpdateSourceTrigger=PropertyChanged}" ElementStyle="{StaticResource CellErrorStyle}"> 
    <DataGridTextColumn.EditingElementStyle> 
      <Style TargetType="TextBox" BasedOn="{StaticResource OriginalStyleKey}"> 
       <Setter Property="MaxLength" Value="5" />        
      </Style> 
    </DataGridTextColumn.EditingElementStyle> 
</DataGridTextColumn>