Come impostare la lunghezza massima per la casella combinata in WPF?

Question

Come impostare maxlength in una casella combinata, a cui è applicato uno stile.

Grazie

Answer 1

quando si utilizza DependencyProperty, possiamo impostare la maxlength della casella combinata senza modificare il vostro stile/modello. esempio

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); 
      }; 
    } 
} 

utilizzati:

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

Dove ComboboxHelper è:

xmlns: ComboboxHelper = "clr- namespace: yourNameSpace; assemblaggio = YourAssembly"

comboBox.FindChild (...) il metodo è registrato here.

Answer 2

Sei corretto. C'è una lunghezza massima per una casella di testo, ma non per una casella combinata. Devi eseguire il rollover utilizzando una casella di testo come intermediario. Ecco po 'di codice:

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 3

questo campo testo è in arrivo nullo. Lo stile indicato è il seguente.

<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

Oppure si può usare l'Attivato o evento Loaded della casella combinata per l'impostazione della maxlength.If il maxlength fai cambiare troppo durante il runtime è possibile utilizzare evento caricato oppure usare Attivato evento

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

e nel rispettivo evento ...

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

Answer 5

ho trovato facile soluzione tramite XAML. Nelle risorse di comboBox possiamo impostare lo stile per textbox e set 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> 

EDIT: Questo funziona con Actipro ComboBox. Per il solito comboBox per fare questo lavoro, date un'occhiata here

Answer 6

Ho usato l'evento PreviewKeyDown, molto semplice + potete mostrare avvertimenti o qualcosa del genere.
Registrare il metodo di seguito in ComboBox.PreviewKeyDown + = evento,
L'evento KeyDown non si attiva se l'utente preme Spazio.

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 :) 
     } 
    } 
}