Como: Adicionar uma marca d'água a um TextBox
The following example shows how to aid usability of a TextBox by displaying an explanatory background image inside of the TextBox until the user inputs text, at which point the image is removed. In addition, the background image is restored again if the user removes their input. See illustration below.
.png "Uma TextBox com uma imagem de plano de fundo")
Observação
The reason a background image is used in this example rather then simply manipulating the Text property of TextBox, is that a background image will not interfere with data binding.
Exemplo
<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;
}
}
}
}