Focus Textbox en utilisant seulement XAML

Question

J'essaie de mettre le focus sur le clavier d'une zone de texte qui est incluse dans un stackpanel réduit par défaut. Lorsque le stackpanel devient visible, je veux que la zone de texte devienne, par défaut, focalisée.

J'ai essayé ce code :

<StackPanel Orientation="Vertical" FocusManager.FocusedElement="{Binding ElementName=TxtB}">
  <TextBox x:Name="TxtA" Text="A" />
  <TextBox x:Name="TxtB" Text="B" />
</StackPanel>

Cependant, cela n'a pas fonctionné. Le curseur de saisie s'est affiché, mais il ne clignotait pas et ne permettait pas d'écrire.

Est-il possible de résoudre mon problème en utilisant uniquement XAML ? Peut-être des déclencheurs ?

Answer 1

Oui, comme vous l'avez dit vous-même, une simple gâchette semble faire l'affaire :

<StackPanel Orientation="Vertical">
    <StackPanel.Style>
       <Style TargetType="StackPanel">
          <Style.Triggers>
              <Trigger Property="Visibility" Value="Visible">
                  <Setter Property="FocusManager.FocusedElement" 
                          Value="{Binding ElementName=TxtA}" />
              </Trigger>
          </Style.Triggers>
       </Style>
    </StackPanel.Style>

    <TextBox x:Name="TxtA" Text="A" />
    <TextBox x:Name="TxtB" Text="B" />
</StackPanel>

Answer 2

Vous devez créer une propriété jointe IsFocused qui appellera la méthode Focus() de l'élément joint si elle vaut true. Attendez, je vais ajouter du code.

public static class FocusHelper
    {
        static FocusHelper()
        {
            var fpmd = new FrameworkPropertyMetadata(null, FrameworkPropertyMetadataOptions.BindsTwoWayByDefault, HandleAttachedIsFocusedChanged) { DefaultUpdateSourceTrigger = UpdateSourceTrigger.PropertyChanged };
            IsFocusedProperty = DependencyProperty.RegisterAttached("IsFocused", typeof(bool?), typeof(FocusHelper), fpmd);
        }

        public static readonly DependencyProperty IsFocusedProperty;

        [Conditional("DEBUG")]
        public static void StartFocusTracing()
        {
            FocusManager.FocusedElementProperty.OverrideMetadata(typeof(FrameworkElement), new PropertyMetadata(HandleFocusedElementChanged));
        }

        private static void HandleFocusedElementChanged(DependencyObject o, DependencyPropertyChangedEventArgs args)
        {
            var element = args.NewValue as FrameworkElement;
            if (element == null)
            {
                Debug.WriteLine("Focus is lost");
                return;
            }

            Debug.WriteLine("Focus moved to {0} type {1}", element.Name, element.GetType().Name);

            var fs = FocusManager.GetFocusScope(element) as FrameworkElement;
            if (fs == null)
                return;

            Debug.WriteLine("Focus scope {0} of type {1}", fs.Name, fs.GetType().Name);
        }

        public static bool? GetIsFocused(DependencyObject element)
        {
            if (element == null)
            {
                throw new ArgumentNullException("element");
            }

            return (bool?)element.GetValue(IsFocusedProperty);
        }

        public static void SetIsFocused(DependencyObject element, bool? value)
        {
            if (element == null)
                throw new ArgumentNullException("element");

            element.SetValue(IsFocusedProperty, value);
        }

        private static void HandleAttachedIsFocusedChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
        {
            WriteDependencyPropertyBindingInformation(d, IsFocusedProperty);

            var fe = (UIElement)d;

            // значение ранее было не задано
            if (e.OldValue == null)
            {
                var pd = DependencyPropertyDescriptor.FromProperty(UIElement.IsFocusedProperty, typeof(UIElement));
                pd.AddValueChanged(fe, HandleUIElementIsFocusedChanged);
            }

            if (e.NewValue == null)
            {
                var pd = DependencyPropertyDescriptor.FromProperty(UIElement.IsFocusedProperty, typeof(UIElement));
                pd.RemoveValueChanged(fe, HandleUIElementIsFocusedChanged);
                return;
            }

            if ((bool)e.NewValue)
            {
                Action setFocus = () =>
                    {
                        IInputElement elementToBeFocused = null;
                        IInputElement finalyFocusedElement = null;
                        // If current element is Focus Scope we try to restore logical focus
                        if (FocusManager.GetIsFocusScope(fe))
                        {
                            elementToBeFocused = FocusManager.GetFocusedElement(fe);
                            if (elementToBeFocused != null)
                            {
                                finalyFocusedElement = Keyboard.Focus(elementToBeFocused);
                            }
                        }

                        // If focus was not restored we try to focus
                        if (finalyFocusedElement == null
                            || (elementToBeFocused != finalyFocusedElement))
                        {
                            fe.FocusThisOrChild();
                        }
                    };
                if (ReflectionHelper.IsInMethod("MeasureOverride", typeof(FrameworkElement))) // hack of layout issue
                    Dispatcher.CurrentDispatcher.BeginInvoke(setFocus);
                else
                    setFocus();
            }
        }

        [Conditional("DEBUG")]
        private static void WriteDependencyPropertyBindingInformation(DependencyObject d, DependencyProperty property)
        {
            var binding = BindingOperations.GetBindingBase(d, IsFocusedProperty);

            if (binding == null)
            {
                Debug.WriteLine("Property {1} of object {0} has no bindings.", d, property.Name);
            }
            else
            {
                Debug.WriteLine("Property {1} of object {0} has binding.", d, property.Name);
                Debug.WriteLine("Type {0}", binding.GetType());

                var expressionBase = BindingOperations.GetBindingExpressionBase(d, IsFocusedProperty);
                Debug.Assert(expressionBase != null);

                Debug.WriteLine("Status {0}", expressionBase.Status);

                var expression = expressionBase as BindingExpression;
                if (expression != null)
                {
                    Debug.WriteLine("Source type {0}", expression.DataItem.GetType());
                    Debug.WriteLine("Source {0}",expression.DataItem);
                }
            }
        }   

        private static void HandleUIElementIsFocusedChanged(object sender, EventArgs e)
        {
            var uiElement = sender as UIElement;
            var isFocused = uiElement.IsFocused;
            ((DependencyObject)sender).SetCurrentValue(IsFocusedProperty, isFocused);
        }

        /// <summary>
        /// Tries to set focus to the element or any child element inside this one.
        /// Tab index is respected
        /// </summary>
        public static bool FocusThisOrChild(this DependencyObject element)
        {
            if (element == null)
                throw new ArgumentNullException("element");

            var inputElement = element as IInputElement;
            var wasFocused = inputElement != null && inputElement.Focus();

            if (!wasFocused)
            {
                element.SetFocusWithin();
            }

            return true;
        }

        public static bool SetFocusWithin(this DependencyObject element)
        {
            if (element == null)
                throw new ArgumentNullException("element");

            var children = element.GetVisualChildrenSortedByTabIndex();
            return children.Any(FocusThisOrChild);
        }
    }

et des méthodes d'aide :

public static IEnumerable<DependencyObject> GetVisualChildrenSortedByTabIndex(this DependencyObject parent)
        {
            if (parent == null)
                throw new ArgumentNullException("parent");

            return parent.GetVisualChildren().OrderBy(KeyboardNavigation.GetTabIndex);
        }

public static bool IsInMethod(string methodName, Type ownerType, bool isStatic = false)
        {
            if (string.IsNullOrWhiteSpace(methodName))
                throw new ArgumentNullException("methodName");

            if (ownerType == null)
                throw new ArgumentNullException("ownerType");

            var stackTrace = new StackTrace(false);
            var isInMethod = stackTrace.GetFrames().Skip(1).Any(frame =>
                       {
                           var method = frame.GetMethod();
                           return method.Name == methodName
                                  && method.IsStatic == isStatic
                                  && ownerType.IsAssignableFrom(method.ReflectedType);
                       });

            return isInMethod;
        }