WPFテキストボックスに消える透かしを実装する方法は？

テキストボックスの透かし

ユーザーが入力を開始すると自動的に消えるテキストボックスにテキストを含めることができます。 🎜>

添付のプロパティソリューション

このソリューションは、添付のプロパティを使用して、テキストボックスに透かし機能を追加します：

watermarkservice.cs

using System;
using System.Windows;
using System.Windows.Controls;

public static class WatermarkService
{
    public static DependencyProperty WatermarkProperty = DependencyProperty.RegisterAttached(
        "Watermark",
        typeof(object),
        typeof(WatermarkService),
        new FrameworkPropertyMetadata((object)null, OnWatermarkChanged)
    );

    public static object GetWatermark(DependencyObject d)
    {
        return (object)d.GetValue(WatermarkProperty);
    }

    public static void SetWatermark(DependencyObject d, object value)
    {
        d.SetValue(WatermarkProperty, value);
    }

    private static void OnWatermarkChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
    {
        Control control = (Control)d;
        control.Loaded += Control_Loaded;

        if (d is TextBox)
        {
            control.GotKeyboardFocus += Control_GotKeyboardFocus;
            control.LostKeyboardFocus += Control_Loaded;
            ((TextBox)control).TextChanged += Control_GotKeyboardFocus;
        }
    }

    private static void Control_GotKeyboardFocus(object sender, RoutedEventArgs e)
    {
        Control c = (Control)sender;
        if (ShouldShowWatermark(c))
        {
            ShowWatermark(c);
        }
        else
        {
            RemoveWatermark(c);
        }
    }

    private static void Control_Loaded(object sender, RoutedEventArgs e)
    {
        Control control = (Control)sender;
        if (ShouldShowWatermark(control))
        {
            ShowWatermark(control);
        }
    }

    private static void RemoveWatermark(UIElement control)
    {
        AdornerLayer layer = AdornerLayer.GetAdornerLayer(control);

        if (layer != null)
        {
            Adorner[] adorners = layer.GetAdorners(control);
            if (adorners == null)
            {
                return;
            }

            foreach (Adorner adorner in adorners)
            {
                if (adorner is WatermarkAdorner)
                {
                    adorner.Visibility = Visibility.Hidden;
                    layer.Remove(adorner);
                }
            }
        }
    }

    private static void ShowWatermark(Control control)
    {
        AdornerLayer layer = AdornerLayer.GetAdornerLayer(control);

        if (layer != null)
        {
            layer.Add(new WatermarkAdorner(control, GetWatermark(control)));
        }
    }

    private static bool ShouldShowWatermark(Control c)
    {
        if (c is TextBox)
        {
            return (c as TextBox).Text == string.Empty;
        }
        else
        {
            return false;
        }
    }
}

watermarkadorner.cs

using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Media;

internal class WatermarkAdorner : Adorner
{
    private ContentPresenter contentPresenter;

    public WatermarkAdorner(UIElement adornedElement, object watermark) :
       base(adornedElement)
    {
        this.IsHitTestVisible = false;

        this.contentPresenter = new ContentPresenter();
        this.contentPresenter.Content = watermark;
        this.contentPresenter.Opacity = 0.5;
        this.contentPresenter.Margin = new Thickness(Control.Margin.Left + Control.Padding.Left, Control.Margin.Top + Control.Padding.Top, 0, 0);

        // Hide the control adorner when the adorned element is hidden
        Binding binding = new Binding("IsVisible");
        binding.Source = adornedElement;
        binding.Converter = new BooleanToVisibilityConverter();
        this.SetBinding(VisibilityProperty, binding);
    }

    protected override int VisualChildrenCount
    {
        get { return 1; }
    }

    private Control Control
    {
        get { return (Control)this.AdornedElement; }
    }

    protected override Visual GetVisualChild(int index)
    {
        return this.contentPresenter;
    }

    protected override Size MeasureOverride(Size constraint)
    {
        this.contentPresenter.Measure(Control.RenderSize);
        return Control.RenderSize;
    }

    protected override Size ArrangeOverride(Size finalSize)
    {
        this.contentPresenter.Arrange(new Rect(finalSize));
        return finalSize;
    }
}

次に、このコードを使用して任意のテキストボックスに透かしを追加します。

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