1、如何判断TextBox是否为空？
if(textbox.Text != string.empty) //或者 if（textbox.Text.Trim()!=""）
{ }
2、设置TextBox为空时，背景文字提示
参考博客：http://www.cnblogs.com/tsunami/archive/2011/09/16/2179170.html
<TextBox FontSize="17" Height="26" Margin="230,150,189,0" Name="txt_Account" VerticalAlignment="Top" Foreground="Indigo" TabIndex="0" BorderThickness="1">
<TextBox.Resources>
<VisualBrush x:Key="HelpBrush" TileMode="None" Opacity="0.3" Stretch="None" AlignmentX="Left">
<VisualBrush.Visual>
<TextBlock FontStyle="Italic" Text="请输入用户名"/>
</VisualBrush.Visual>
</VisualBrush>
</TextBox.Resources>
<TextBox.Style>
<Style TargetType="TextBox">
<Style.Triggers>
<Trigger Property="Text" Value="{x:Null}">
<Setter Property="Background" Value="{StaticResource HelpBrush}"/>
</Trigger>
<Trigger Property="Text" Value="">
<Setter Property="Background" Value="{StaticResource HelpBrush}"/>
</Trigger>
</Style.Triggers>
</Style>
</TextBox.Style>
</TextBox>
在Stackoverflow上的回答也很好http://stackoverflow.com/questions/833943/watermark-hint-text-placeholder-textbox-in-wpf/21672408#21672408
以下这个回答使用资源实现
<Window.Resources>
<Style x:Key="TextBoxUserStyle" BasedOn="{x:Null}" TargetType="{x:Type TextBox}">
<Setter Property="Foreground" Value="Black"/>
<Setter Property="HorizontalAlignment" Value="Center"/>
<Setter Property="VerticalContentAlignment" Value="Center"/>
<Setter Property="Width" Value="225"/>
<Setter Property="Height" Value="25"/>
<Setter Property="FontSize" Value="12"/>
<Setter Property="Padding" Value="1"/>
<Setter Property="Margin" Value="5"/>
<Setter Property="AllowDrop" Value="true"/>
<Setter Property="FocusVisualStyle" Value="{x:Null}"/>
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="{x:Type TextBox}">
<Border x:Name="OuterBorder" BorderBrush="#5AFFFFFF" BorderThickness="1,1,1,1" CornerRadius="4,4,4,4">
<Border x:Name="InnerBorder" Background="#FFFFFFFF" BorderBrush="#33000000" BorderThickness="1,1,1,1" CornerRadius="3,3,3,3">
<ScrollViewer SnapsToDevicePixels="{TemplateBinding SnapsToDevicePixels}" x:Name="PART_ContentHost"/>
</Border>
</Border>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
<Style x:Key="PasswordBoxVistaStyle" BasedOn="{x:Null}" TargetType="{x:Type PasswordBox}">
<Setter Property="Foreground" Value="Black"/>
<Setter Property="HorizontalAlignment" Value="Center"/>
<Setter Property="VerticalContentAlignment" Value="Center"/>
<Setter Property="Width" Value="225"/>
<Setter Property="Height" Value="25"/>
<Setter Property="FontSize" Value="12"/>
<Setter Property="Padding" Value="1"/>
<Setter Property="Margin" Value="5"/>
<Setter Property="AllowDrop" Value="true"/>
<Setter Property="FocusVisualStyle" Value="{x:Null}"/>
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="{x:Type PasswordBox}">
<Border x:Name="OuterBorder" BorderBrush="#5AFFFFFF" BorderThickness="1,1,1,1" CornerRadius="4,4,4,4">
<Border x:Name="InnerBorder" Background="#FFFFFFFF" BorderBrush="#33000000" BorderThickness="1,1,1,1" CornerRadius="3,3,3,3">
<Grid>
<Label x:Name="lblPwd" Content="Password" FontSize="11" VerticalAlignment="Center" Margin="2,0,0,0" FontFamily="Verdana" Foreground="#828385" Padding="0"/>
<ScrollViewer SnapsToDevicePixels="{TemplateBinding SnapsToDevicePixels}" x:Name="PART_ContentHost"/>
</Grid>
</Border>
</Border>
<ControlTemplate.Triggers>
<Trigger Property="IsFocused" Value="True">
<Setter Property="Visibility" TargetName="lblPwd" Value="Hidden"/>
</Trigger>
</ControlTemplate.Triggers>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
</Window.Resources>
<PasswordBox Style="{StaticResource PasswordBoxVistaStyle}" Margin="169,143,22,0" Name="txtPassword" FontSize="14" TabIndex="2" Height="31" VerticalAlignment="Top" />使用第一种方式实现PasswordBox的话需要设置依赖属性，因为PasswordBox中的Password不是依赖属性，需要自己实现。留作以后研究
3、自己写UserControl实现PasswordBox和TextBox的水印
参考博客：http://www.cnblogs.com/zhanglee/archive/2012/10/20/2732097.html
贴出PasswordBox的代码，侵删
<UserControl
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
mc:Ignorable="d"
x:Class="WpfApplication1.MyPassword"
x:Name="UserControl"
d:DesignWidth="150" d:DesignHeight="26"> <Grid x:Name="LayoutRoot">
<Border Background="White" Padding="2,3" Margin="1" d:LayoutOverrides="VerticalAlignment, GridBox"/>
<TextBlock Text="请输入密码" x:Name="txtPasswordTip" Padding="7,3" Margin="1,3,1,1" FontFamily="SimSun" d:LayoutOverrides="VerticalAlignment, GridBox"/>
<PasswordBox Padding="4,3,2,3" Background="Transparent" x:Name="password" PasswordChanged="password_PasswordChanged" d:LayoutOverrides="GridBox" Password=""/>
</Grid>
</UserControl>
using System;
using System.Collections.Generic;
using System.Text;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Navigation;
using System.Windows.Shapes; namespace WpfApplication1
{
/// <summary>
/// MyPassword.xaml 的交互逻辑
/// </summary>
public partial class MyPassword : UserControl
{
public MyPassword()
{
this.InitializeComponent();
if (string.IsNullOrWhiteSpace(TipContent))
{
_tipContent = "请输入密码";
}
txtPasswordTip.Text = TipContent;
} string tip = string.Empty;
private void password_PasswordChanged(object sender, RoutedEventArgs e)
{ if (password.Password.Length != )
{
// this.Content = password.Password;
this._Password = password.Password;
if (!string.IsNullOrWhiteSpace(txtPasswordTip.Text))
tip = txtPasswordTip.Text;
txtPasswordTip.Text = string.Empty;
}
else { txtPasswordTip.Text = tip; }
} private string _tipContent = string.Empty;
public string TipContent
{
get
{
return _tipContent;
}
set
{
if (value != _tipContent)
{
_tipContent = value;
txtPasswordTip.Text = TipContent;
}
}
} private string _Password = string.Empty;
public string Password
{
get
{
return _Password;
}
set
{
if (value != _Password)
{
_Password = value; }
}
} }
}
待更新.......