How to Create a TextBox Watermark Using Attached Properties in WPF?

Use additional attributes to create TextBox watermark

Before the user input, it is very useful to provide users with guidance or placeholder text. At this time, it is particularly important to create a watermark in TextBox. When the user starts input, this text will disappear automatically.

Create watermarks with additional attributes

To create a watermark, you can use additional attributes and the WaterMarkadorner class provided below:

Use watermark

<code class="language-csharp">/// <summary>
/// 提供水印附加属性的类
/// </summary>
public static class WatermarkService
{
    /// <summary>
    /// 水印附加依赖属性
    /// </summary>
    public static readonly DependencyProperty WatermarkProperty = DependencyProperty.RegisterAttached(
        "Watermark",
        typeof(object),
        typeof(WatermarkService),
        new FrameworkPropertyMetadata((object)null, new PropertyChangedCallback(OnWatermarkChanged)));

    // ...
}</code>

<code class="language-csharp">/// <summary>
/// 水印装饰器
/// </summary>
internal class WatermarkAdorner : Adorner
{
    // ...
}</code>

After defining these classes, you can use the following code to add the watermark to any Textbox:

Please note that this watermark can be applied to other controls, including Combobox and ItemControls.

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