How can I implement a disappearing watermark in a TextBox using WPF?

This text describes how to implement a disappearing watermark in a WPF TextBox using an attached property and adorner. Let's rephrase it while maintaining the core information and preserving the image's original format.

Creating a Disappearing Watermark for WPF TextBoxes

Enhance your WPF TextBox controls with a helpful watermark that vanishes as the user begins typing. This guide demonstrates how to implement this feature using an attached property and an adorner.

The solution leverages a custom WatermarkService attached property. Here's the code for WatermarkService:

// WatermarkService.cs
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Controls.Primitives;
using System.Windows.Documents;

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

    // ... (rest of the WatermarkService code remains unchanged) ...
}

The WatermarkService manages the display and hiding of the watermark. It uses a WatermarkAdorner (code not fully shown but implied) to overlay the watermark text onto the TextBox. The key functionality lies in the event handlers within WatermarkService that dynamically show or hide the adorner based on whether the TextBox is empty.

To utilize this WatermarkService, you would apply it as an attached property to your TextBox in XAML, specifying the watermark text. The provided WatermarkAdorner class (code partially omitted) handles the visual presentation of the watermark. The complete code for WatermarkAdorner would be needed for full implementation. The logic within WatermarkService ensures the watermark appears only when the TextBox is empty and disappears when the user starts typing.

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