WPF 之 文本框及密码框添加水印效果

1、文本框添加水印效果

　　文本框水印相对简单，不需要重写模板，仅仅需要一个 VisualBrush 和触发器验证一下Text是否为空即可。

<TextBox Name="txtSerachDataName" Width="120" Height="23" Grid.Column="3" Grid.Row="1">
            <TextBox.Resources>
                <VisualBrush x:Key="HelpBrush" TileMode="None" Opacity="0.3" Stretch="None" AlignmentX="Left">
                    <VisualBrush.Visual>
                        <TextBlock FontStyle="Italic" Text="水印效果"/>
                    </VisualBrush.Visual>
                </VisualBrush>
            </TextBox.Resources>
            <TextBox.Style>
                <Style TargetType="TextBox">
                    <Setter Property="Height" Value="23"></Setter>
                    <Setter Property="HorizontalAlignment" Value="Left"></Setter>
                    <Setter Property="VerticalAlignment" Value="Top"></Setter>
                    <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>

2、密码框添加水印效果

　　关于密码框水印就不同于文本框了，可以写个Brush就搞定，因为密码框是没有可以用于判断输入非空的依赖属性的，这就需要我们去加一个，代码如下：

　　 public class PasswordBoxMonitor : DependencyObject
    {
        public static bool GetIsMonitoring(DependencyObject obj)
        {
            return (bool)obj.GetValue(IsMonitoringProperty);
        }

        public static void SetIsMonitoring(DependencyObject obj, bool value)
        {
            obj.SetValue(IsMonitoringProperty, value);
        }

        public static readonly DependencyProperty IsMonitoringProperty =
            DependencyProperty.RegisterAttached("IsMonitoring", typeof(bool), typeof(PasswordBoxMonitor), new UIPropertyMetadata(false, OnIsMonitoringChanged));

        public static int GetPasswordLength(DependencyObject obj)
        {
            return (int)obj.GetValue(PasswordLengthProperty);
        }

        public static void SetPasswordLength(DependencyObject obj, int value)
        {
            obj.SetValue(PasswordLengthProperty, value);
        }

        public static readonly DependencyProperty PasswordLengthProperty =
            DependencyProperty.RegisterAttached("PasswordLength", typeof(int), typeof(PasswordBoxMonitor), new UIPropertyMetadata());

        private static void OnIsMonitoringChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
        {
            var pb = d as PasswordBox;
            if (pb == null)
            {
                return;
            }
            if ((bool)e.NewValue)
            {
                pb.PasswordChanged += PasswordChanged;
            }
            else
            {
                pb.PasswordChanged -= PasswordChanged;
            }
        }

        static void PasswordChanged(object sender, RoutedEventArgs e)
        {
            var pb = sender as PasswordBox;
            if (pb == null)
            {
                return;
            }
            SetPasswordLength(pb, pb.Password.Length);
        }
    }

　　加一个PasswordLength  用于判断密码框长度是否为0，当为0的时候就显示水印，否则就隐藏。

　　在使用重构的PasswordBox的时候需要去引用一下：xmlns:WpfTest="clr-namespace:WpfApplication2"，WpfApplication2为项目的命名空间。

<PasswordBox Name="pb" Width="120" VerticalAlignment="Bottom" Height="35"  Grid.Column="3" Grid.Row="3">
　　<PasswordBox.Style>
   　　<Style TargetType="PasswordBox">
      　　<Setter Property="Height" Value="23"></Setter>
         <Setter Property="HorizontalAlignment" Value="Left"></Setter>
         <Setter Property="VerticalAlignment" Value="Top"></Setter>
         <Setter Property="WpfTest:PasswordBoxMonitor.IsMonitoring"  Value="True"/>
         <Setter Property="Template">
             <Setter.Value>
                 <ControlTemplate TargetType="{x:Type PasswordBox}">
                     <Border Name="Bd"  Background="{TemplateBinding Background}"  BorderThickness="{TemplateBinding BorderThickness}"
                           BorderBrush="{TemplateBinding BorderBrush}"  SnapsToDevicePixels="true">
                          <Grid>
                              <ScrollViewer x:Name="PART_ContentHost" SnapsToDevicePixels="{TemplateBinding SnapsToDevicePixels}"/>
                                  <StackPanel Orientation="Horizontal" Visibility="Collapsed" Name="myStackPanel">
　　　　　　　　　　　　　　　　　　　　 　　<TextBlock HorizontalAlignment="Left" VerticalAlignment="Center" Foreground="LightGray" Text="水印效果"/>
                                  </StackPanel>
                          </Grid>
                      </Border>
                      <ControlTemplate.Triggers>
                          <Trigger Property="IsEnabled" Value="false">
                              <Setter Property="Visibility" TargetName="myStackPanel" Value="Collapsed"/>
                          </Trigger>
                          <Trigger Property="WpfTest:PasswordBoxMonitor.PasswordLength" Value="0">
                              <Setter Property="Visibility" TargetName="myStackPanel" Value="Visible"/>
                          </Trigger>
                       </ControlTemplate.Triggers>
                   </ControlTemplate>
                </Setter.Value>
            </Setter>
        </Style>
    </PasswordBox.Style>
</PasswordBox>

　　如上面的代码，重写了一下ControlTemplate，加了一个StackPanel，判断一下密码框的内容长度，不为0的时候显示StanckPanel   否则不显示。

　　当然也可以不使用模板，像文本框里面的那种方式去显示，只是给PasswordBox注册一个依赖属性即可，这里只是多说明一种使用方式，根据不同的情况可选择适用的方式。