WPF有水印的TextBox(WaterMark)

之前已经有实现过一个水印的TextBox，思路是TextBox在捕获和丢失焦点时，根据Text的值是否为空，修改Text的颜色和值，来达到水印目的。但是这种操作方法其实有一个明显的弊端，WPF用的最多的就是Binding,TextBox的Text属性用于Binding的就更多了；不仅如此，我们有时还希望自己能够定义水印的名称。因此，通过修改TextBox的控件模板，实现水印是一个更好的选择。

代码很简单，直接上：

<ResourceDictionary

    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"

    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"

    xmlns:local="clr-namespace:MyWPFControlsLib">

    <Style TargetType="{x:Type local:MyWatermark}">

        <Setter Property="BorderBrush" Value="Gray"/>

        <Setter Property="BorderThickness" Value="1"/>

        <Setter Property="Template">

            <Setter.Value>

                <ControlTemplate TargetType="{x:Type local:MyWatermark}">

                    <Border x:Name="Bd" BorderBrush="{TemplateBinding BorderBrush}" BorderThickness="{TemplateBinding BorderThickness}" Background="{TemplateBinding Background}"  SnapsToDevicePixels="True">

                        <Grid>

                            <ScrollViewer x:Name="PART_ContentHost" SnapsToDevicePixels="{TemplateBinding SnapsToDevicePixels}"/>

                            <TextBlock x:Name="Message" VerticalAlignment="Center" Foreground="LightGray" Padding="3,0,0,0" Text="{TemplateBinding WaterMark}" Visibility="Hidden"/>

                        </Grid>

                    </Border>

                    <ControlTemplate.Triggers>

                        <DataTrigger Binding="{Binding RelativeSource={RelativeSource Self}, Path=Text}" Value="">

                            <Setter TargetName="Message" Property="Visibility" Value="Visible" />

                        </DataTrigger>

                        <Trigger Property="IsEnabled" Value="False">

                            <Setter Property="Background" TargetName="Bd" Value="{DynamicResource {x:Static SystemColors.ControlBrushKey}}"/>

                            <Setter Property="Foreground" Value="{DynamicResource {x:Static SystemColors.GrayTextBrushKey}}"/>

                        </Trigger>

                    </ControlTemplate.Triggers>

                </ControlTemplate>

            </Setter.Value>

        </Setter>

    </Style>

</ResourceDictionary>

下面的这张图片，请注意，这里我用了个DataTrigger,为什么这么用，请自行理解：



using System;

using System.Collections.Generic;

using System.Linq;

using System.Text;

using System.Windows;

using System.Windows.Controls;

namespace MyWPFControlsLib

{

    public class MyWatermark:TextBox

    {

        static MyWatermark()

        {

            //这句话就是告诉应用程序可以在Themes/Generic文件夹下找到样式，否则，另一个程序集使用则需要添加类似如何的<!--<ResourceDictionary Source="pack://application:,,,/MyWPFControlsLib;component/Themes/Generic.xaml"/>-->引用

            DefaultStyleKeyProperty.OverrideMetadata(typeof(MyWatermark), new FrameworkPropertyMetadata(typeof(MyWatermark)));

        }

        public static readonly DependencyProperty WaterMarkProperty = DependencyProperty.Register("WaterMark", typeof(string), typeof(MyWatermark), new PropertyMetadata("请输入文本"));

        public string WaterMark

        {

            get { return (string)GetValue(WaterMarkProperty); }

            set { SetValue(WaterMarkProperty, value); }

        }

    }

}

以上是控件的全部代码，你可以编译成dll，然后引用并使用它。最后上使用的时的代码，并附个效果图：

<Window x:Class="MyWPFControls.Test.MainWindow"

        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"

        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"

        xmlns:my="clr-namespace:MyWPFControlsLib;assembly=MyWPFControlsLib"

        Title="MainWindow" Height="350" Width="525">

    <Grid>

        <my:MyWatermark Width="200" Height="25" Padding="3" WaterMark="请输入数值"/>

    </Grid>

</Window>



到此全部结束。