HOW TO：將浮水印加入至 TextBox

下列範例顯示如何增加 TextBox 的可用性，方式是在 TextBox 內顯示說明背景影像，直到使用者輸入文字時才移除影像。 此外，當使用者移除輸入內容時會再度還原背景影像。 請參閱下圖。

注意事項
本範例中使用背景影像而非簡單操作 TextBox 的 Text 屬性的原因，是背景影像不會妨礙資料繫結。

範例

<Page
  xmlns="https://schemas.microsoft.com/winfx/2006/xaml/presentation"
  xmlns:x="https://schemas.microsoft.com/winfx/2006/xaml"
  x:Class="SDKSample.TextBoxBackgroundExample"
  >

  <StackPanel>
    <TextBox Name="myTextBox" TextChanged="OnTextBoxTextChanged" Width="200">
      <TextBox.Background>
        <ImageBrush ImageSource="TextBoxBackground.gif" AlignmentX="Left" Stretch="None" />
      </TextBox.Background>
    </TextBox>
  </StackPanel>
</Page>

Namespace SDKSample
    Partial Public Class TextBoxBackgroundExample
        Inherits Page

        Private Sub OnTextBoxTextChanged(ByVal sender As Object, ByVal e As TextChangedEventArgs)

            If myTextBox.Text = "" Then

                ' Create an ImageBrush.
                Dim textImageBrush As New ImageBrush()

                textImageBrush.ImageSource =
                    New BitmapImage(New Uri("TextBoxBackground.gif", UriKind.Relative))
                textImageBrush.AlignmentX = AlignmentX.Left
                textImageBrush.Stretch = Stretch.None

                ' Use the brush to paint the button's background.
                myTextBox.Background = textImageBrush

            Else

                myTextBox.Background = Nothing
            End If

        End Sub

    End Class

End Namespace

using System;
using System.Windows;
using System.Windows.Input;
using System.Windows.Controls;
using System.Windows.Media;
using System.Windows.Media.Imaging;

namespace SDKSample
{
    public partial class TextBoxBackgroundExample : Page
    {

        void OnTextBoxTextChanged(object sender, TextChangedEventArgs e)
        {

            if (myTextBox.Text == "")
            {
                // Create an ImageBrush.
                ImageBrush textImageBrush = new ImageBrush();
                textImageBrush.ImageSource =
                    new BitmapImage(
                        new Uri(@"TextBoxBackground.gif", UriKind.Relative)
                    );
                textImageBrush.AlignmentX = AlignmentX.Left;
                textImageBrush.Stretch = Stretch.None;
                // Use the brush to paint the button's background.
                myTextBox.Background = textImageBrush;

            }
            else
            {

                myTextBox.Background = null;
            }

        }

    }

}

請參閱

概念

TextBox 概觀

RichTextBox 概觀