WPF带占位符的TextBox
标签：route blog move ade ted property etc src style
原文:WPF带占位符的TextBox
简介
效果图如下：
使用的XAML代码如下：
Window x:Class="PlaceHolderTextBox.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:local="clr-namespace:PlaceHolderTextBox"
Title="MainWindow"
Width="525"
Height="350">
StackPanel>
local:PlaceholderTextBox Placeholder="查询" />
TextBox x:Name="TxtTest" local:PlaceholderManager.Placeholder="搜索" />
StackPanel>
Window>
其中第一个是带占位符的文本框，第二个使用附加属性装饰在现有的文本框上。
原理
将一个与占位符绑定的TextBlock放入VisualBrush内，在TextBox的Text为空时使用VisualBrush绘制背景，不为空时背景设为Null。
正因为如此，如果文本框设置了背景，使用此方法就会覆盖原有的背景。但一般不会设置TextBox的背景。
带占位符的文本框
代码较简单，如下：
using System.Globalization;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Media;
namespace PlaceHolderTextBox
{
///
/// 带点位符的文本输入控件
///
public class PlaceholderTextBox:TextBox
{
#region Fields
///
/// 占位符的文本框
///
private readonly TextBlock _placeholderTextBlock = new TextBlock();
///
/// 占位符的画刷
///
private readonly VisualBrush _placeholderVisualBrush = new VisualBrush();
#endregion Fields
#region Properties
///
/// 占位符的依赖属性
///
public static readonly DependencyProperty PlaceholderProperty = DependencyProperty.Register(
"Placeholder", typeof (string), typeof (PlaceholderTextBox),
new FrameworkPropertyMetadata("请在此输入", FrameworkPropertyMetadataOptions.AffectsRender));
///
/// 占位符
///
public string Placeholder
{
get { return (string) GetValue(PlaceholderProperty); }
set { SetValue(PlaceholderProperty, value); }
}
#endregion Properties
#region Public Methods
public PlaceholderTextBox()
{
var binding = new Binding
{
Source = this,
Path = new PropertyPath("Placeholder")
};
_placeholderTextBlock.SetBinding(TextBlock.TextProperty, binding);
_placeholderTextBlock.FontStyle = FontStyles.Italic;
_placeholderVisualBrush.AlignmentX = AlignmentX.Left;
_placeholderVisualBrush.Stretch = Stretch.None;
_placeholderVisualBrush.Visual = _placeholderTextBlock;
Background = _placeholderVisualBrush;
TextChanged += PlaceholderTextBox_TextChanged;
}
#endregion Public Methods
#region Events Handling
///
/// 文本变化的响应
///
///
///
private void PlaceholderTextBox_TextChanged(object sender, TextChangedEventArgs e)
{
Background = string.IsNullOrEmpty(Text) ? _placeholderVisualBrush : null;
}
#endregion Events Handling
}
}
使用附加属性
代码较简单，如下：
using System.Collections.Generic;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Media;
namespace PlaceHolderTextBox
{
///
/// 占位符的管理类
///
public class PlaceholderManager
{
#region Fields
///
/// 文本框和Visual画刷对应的字典
///
private static readonly Dictionary TxtBrushes = new Dictionary();
#endregion Fields
#region Attached DependencyProperty
///
/// 占位符的附加依赖属性
///
public static readonly DependencyProperty PlaceholderProperty = DependencyProperty.RegisterAttached(
"Placeholder", typeof(string), typeof(PlaceholderManager),
new PropertyMetadata("请在此处输入", OnPlaceholderChanged));
///
/// 获取占位符
///
/// 占位符所在的对象
/// 占位符
public static string GetPlaceholder(DependencyObject obj)
{
return (string)obj.GetValue(PlaceholderProperty);
}
///
/// 设置占位符
///
/// 占位符所在的对象
/// 占位符
public static void SetPlaceholder(DependencyObject obj, string value)
{
obj.SetValue(PlaceholderProperty, value);
}
#endregion Attached DependencyProperty
#region Events Handling
///
/// 占位符改变的响应
///
/// 来源
/// 改变信息
public static void OnPlaceholderChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
{
var txt = d as TextBox;
if ((txt != null) && (!TxtBrushes.ContainsKey(txt)))
{
var placeholderTextBlock = new TextBlock();
var binding = new Binding
{
Source = txt,
//绑定到附加属性
Path = new PropertyPath("(0)", PlaceholderProperty)
};
placeholderTextBlock.SetBinding(TextBlock.TextProperty, binding);
placeholderTextBlock.FontStyle = FontStyles.Italic;
var placeholderVisualBrush = new VisualBrush
{
AlignmentX = AlignmentX.Left,
Stretch = Stretch.None,
Visual = placeholderTextBlock
};
txt.Background = placeholderVisualBrush;
txt.TextChanged += PlaceholderTextBox_TextChanged;
txt.Unloaded += PlaceholderTextBox_Unloaded;
TxtBrushes.Add(txt, placeholderVisualBrush);
}
}
///
/// 文本变化的响应
///
///
///
private static void PlaceholderTextBox_TextChanged(object sender, TextChangedEventArgs e)
{
var txt = sender as TextBox;
if ((txt != null) && (TxtBrushes.ContainsKey(txt)))
{
var placeholderVisualBrush = TxtBrushes[txt];
txt.Background = string.IsNullOrEmpty(txt.Text) ? placeholderVisualBrush : null;
}
}
///
/// 文本框卸载的响应
///
///
///
private static void PlaceholderTextBox_Unloaded(object sender, RoutedEventArgs e)
{
var txt = sender as TextBox;
if ((txt != null) && (TxtBrushes.ContainsKey(txt)))
{
TxtBrushes.Remove(txt);
txt.TextChanged -= PlaceholderTextBox_TextChanged;
txt.Unloaded -= PlaceholderTextBox_Unloaded;
}
}
#endregion Events Handling
}
}
WPF带占位符的TextBox
标签：route blog move ade ted property etc src style
原文地址：https://www.cnblogs.com/lonelyxmas/p/10253724.html
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