¿Cómo establecer maxlength para combobox en WPF?

Question

¿Cómo configuro maxlength en el cuadro combinado, que tiene un estilo aplicado a él?

Gracias

Answer 1

Estás en lo correcto. Hay una longitud máxima para un cuadro de texto, pero no para un cuadro combinado. Tienes que hacer tu propio uso de un cuadro de texto como intermediario. Aquí hay un código:

public int MaxLength {get; set;}
protected override void OnGotFocus(System.Windows.RoutedEventArgs e)
{
base.OnGotFocus(e);
TextBox thisTextBox = (TextBox)base.GetTemplateChild("PART_EditableTextBox");
if (thisTextBox != null)
thisTextBox.MaxLength = MaxLength;
}

Answer 2

O puede usar el evento GotFocus o Loaded del cuadro combinado para establecer la longitud máxima. Si la duración máxima cambia demasiado durante el tiempo de ejecución, puede usar evento cargado o utilizar el evento getfocus.

<ComboBox Height="30" IsEditable="True" Loaded="ComboBox_Loaded"/>

y en el evento respectivo ...

 var obj = (ComboBox)sender;
if (obj != null)
{
var myTextBox = (TextBox)obj.Template.FindName("PART_EditableTextBox",obj);
if (myTextBox != null)
{
myTextBox.MaxLength = maxLength;
}
}

Answer 3

Este TextBox es nulo. El estilo dado es el siguiente.

<ControlTemplate x:Key="ComboBoxToggleButton" TargetType="ToggleButton">
<Grid>
<Grid.ColumnDefinitions>
<ColumnDefinition Width="*" />
<ColumnDefinition Width="{Binding Path=(local:ToggleComboBox.Width),
RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type ComboBox}}}" />
</Grid.ColumnDefinitions>
<Border x:Name="Border"
Grid.Column="1"
CornerRadius="2"
Background="#CCFFCC"
BorderBrush="#000080"
BorderThickness="4" />
<Border Grid.Column="0"
CornerRadius="8,8,8,8"
Margin="0"
Background="#CCFFCC"
BorderBrush="#000080"
BorderThickness="4,4,4,4" />
<Image x:Name="Arrow"
Grid.Column="1"
Source="Arrow.png" Margin="4,4,4,4"
HorizontalAlignment="Center"
VerticalAlignment="Center"/>
</Grid>
<ControlTemplate.Triggers>
<Trigger Property="ToggleButton.IsMouseOver" Value="true">
<Setter TargetName="Border" Property="Background" Value="{StaticResource DarkBrush}" />
</Trigger>
<Trigger Property="ToggleButton.IsChecked" Value="true">
<Setter TargetName="Border" Property="Background" Value="{StaticResource PressedBrush}" />
</Trigger>
<Trigger Property="IsEnabled" Value="False">
<Setter TargetName="Border" Property="Background" Value="{StaticResource DisabledBackgroundBrush}" />
<Setter TargetName="Border" Property="BorderBrush" Value="{StaticResource DisabledBorderBrush}" />
<Setter Property="Foreground" Value="{StaticResource DisabledForegroundBrush}"/>
<!--<Setter TargetName="Arrow" Property="Fill" Value="{StaticResource DisabledForegroundBrush}" />-->
</Trigger>
</ControlTemplate.Triggers>
</ControlTemplate>
<ControlTemplate x:Key="ComboBoxTextBox" TargetType="TextBox">
<Border x:Name="PART_ContentHost" Focusable="False" Background="{TemplateBinding Background}" />
</ControlTemplate>
<Style x:Key="ComboBoxStyle" TargetType="ComboBox">
<Setter Property="SnapsToDevicePixels" Value="true"/>
<Setter Property="OverridesDefaultStyle" Value="true"/>
<Setter Property="ScrollViewer.HorizontalScrollBarVisibility" Value="Auto"/>
<Setter Property="ScrollViewer.VerticalScrollBarVisibility" Value="Auto"/>
<Setter Property="ScrollViewer.CanContentScroll" Value="true"/>
<Setter Property="MinWidth" Value="120"/>
<Setter Property="MinHeight" Value="20"/>
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="ComboBox">
<Grid>
<ToggleButton Name="ToggleButton"
Template="{StaticResource ComboBoxToggleButton}"
Grid.Column="2"
Focusable="false"
IsChecked="{Binding Path=IsDropDownOpen,
Mode=TwoWay,
RelativeSource={RelativeSource TemplatedParent}}"
ClickMode="Press"/>
<ContentPresenter Name="ContentSite"
IsHitTestVisible="False"
Content="{TemplateBinding SelectionBoxItem}"
ContentTemplate="{TemplateBinding SelectionBoxItemTemplate}"
ContentTemplateSelector="{TemplateBinding ItemTemplateSelector}"
Margin="9,2,28,2"
VerticalAlignment="Center"
HorizontalAlignment="Left" />
<TextBox x:Name="PART_EditableTextBox"
Style="{x:Null}"
Template="{StaticResource ComboBoxTextBox}"
HorizontalAlignment="Left"
VerticalAlignment="Center"
Margin="3,3,23,3"
Focusable="True"
Background="Transparent"
Visibility="Hidden"
IsReadOnly="{TemplateBinding IsReadOnly}"/>
<Popup Name="Popup"
Placement="Bottom"
IsOpen="{TemplateBinding IsDropDownOpen}"
AllowsTransparency="True"
Focusable="False"
PopupAnimation="Slide">
<Grid Name="DropDown"
SnapsToDevicePixels="True"
MinWidth="{TemplateBinding ActualWidth}"
MaxHeight="{TemplateBinding MaxDropDownHeight}">
<Border x:Name="DropDownBorder"
Background="#CCFFCC"
BorderBrush="#000080"
BorderThickness="2"/>
<ScrollViewer Margin="4,6,4,6" SnapsToDevicePixels="True">
<ScrollViewer.Resources>
<sys:Double x:Key="{x:Static SystemParameters.VerticalScrollBarWidthKey}">25</sys:Double>
</ScrollViewer.Resources>
<StackPanel IsItemsHost="True" />
</ScrollViewer>
</Grid>
</Popup>
</Grid>
<ControlTemplate.Triggers>
<Trigger Property="HasItems" Value="false">
<Setter TargetName="DropDownBorder" Property="MinHeight" Value="95"/>
</Trigger>
<Trigger Property="IsEnabled" Value="false">
<Setter Property="Foreground" Value="{StaticResource DisabledForegroundBrush}"/>
</Trigger>
<Trigger Property="IsGrouping" Value="true">
<Setter Property="ScrollViewer.CanContentScroll" Value="false"/>
</Trigger>
<Trigger SourceName="Popup" Property="Popup.AllowsTransparency" Value="true">
<Setter TargetName="DropDownBorder" Property="CornerRadius" Value="4"/>
<Setter TargetName="DropDownBorder" Property="Margin" Value="0,2,0,0"/>
</Trigger>
<Trigger Property="IsEditable" Value="true">
<Setter Property="IsTabStop" Value="false"/>
<Setter TargetName="PART_EditableTextBox" Property="Visibility" Value="Visible"/>
<Setter TargetName="ContentSite" Property="Visibility" Value="Hidden"/>
</Trigger>
</ControlTemplate.Triggers>
</ControlTemplate>
</Setter.Value>
</Setter>
<Setter Property="ItemContainerStyle" >
<Setter.Value>
<Style TargetType="{x:Type ComboBoxItem}">
<Setter Property="FontSize" Value="20" />
</Style>
</Setter.Value>
</Setter>
</Style>

Answer 4

Usé el evento PreviewKeyDown, muy simple + puede mostrar una advertencia o algo así.
Registre el método a continuación en su ComboBox.PreviewKeyDown + = evento,
El evento KeyDown no se disparará si el usuario presiona Espacio.

private void ComboBox_PreviewKeyDown(object sender, KeyEventArgs e)
{
if (ComboBox.Text.Length > 19) // allow max 20 chars
{
if (e.Key != Key.Back) // allow removing chars
{
e.Handled = true; // block any additional key press if there is more than allowed max
System.Media.SystemSounds.Beep.Play(); // optional: beep to let user know he is out of space :)
}
}
}

Answer 5

Encontré una solución fácil a través de XAML. En los recursos de comboBox podemos establecer el estilo para el cuadro de texto y establecer setter maxlenth.

<ComboBox Name="comboBox" Width="100" IsEditable="True">
<ComboBox.Resources>
<Style TargetType="{x:Type TextBox}">
<Setter Property="MaxLength" Value="yourValue"></Setter>
</Style>
</ComboBox.Resources>
</ComboBox>

EDITAR: Esto funciona con Actipro ComboBox. Para comboBox habitual para hacer esto, mira aquí

Answer 6

Al usar DependencyProperty, podemos establecer la longitud máxima del cuadro combinado sin modificar su estilo / plantilla.

public class EditableComboBox
{
public static int GetMaxLength(DependencyObject obj)
{
return (int)obj.GetValue(MaxLengthProperty);
}
public static void SetMaxLength(DependencyObject obj, int value)
{
obj.SetValue(MaxLengthProperty, value);
}
// Using a DependencyProperty as the backing store for MaxLength. This enables animation, styling, binding, etc...
public static readonly DependencyProperty MaxLengthProperty = DependencyProperty.RegisterAttached("MaxLength", typeof(int), typeof(EditableComboBox), new UIPropertyMetadata(OnMaxLenghtChanged));
private static void OnMaxLenghtChanged(DependencyObject obj, DependencyPropertyChangedEventArgs args)
{
var comboBox = obj as ComboBox;
if (comboBox == null) return;
comboBox.Loaded +=
(s, e) =>
{
var textBox = comboBox.FindChild(typeof(TextBox), "PART_EditableTextBox");
if (textBox == null) return;
textBox.SetValue(TextBox.MaxLengthProperty, args.NewValue);
};
}
}

Ejemplo de uso:

<ComboBox ComboboxHelper:EditableComboBox.MaxLength="50" />

Donde ComboboxHelper es:

xmlns: ComboboxHelper = "clr- namespace: yourNameSpace ; assembly = yourAssembly "

El método comboBox.FindChild (...) se publica aquí .