WPF: 通过Style 为TextBox添加 WarterMark

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1. XAML 代码

<TextBox Width="250" x:Name="UserNameBox" Text="{Binding UserName}" Grid.Row="1" Grid.Column="2" HorizontalAlignment="Right">            <TextBox.Style>                <Style TargetType="TextBox" xmlns:sys="clr-namespace:System;assembly=mscorlib">                    <Style.Resources>                        <VisualBrush x:Key="CueBannerBrush" AlignmentX="Left" AlignmentY="Center" Stretch="None">                            <VisualBrush.Visual>                                <Label Content="{StaticResource LoginEmailHint}" Foreground="Gray" />                            </VisualBrush.Visual>                        </VisualBrush>                    </Style.Resources>                    <Style.Triggers>                        <Trigger Property="Text" Value="{x:Static sys:String.Empty}">                            <Setter Property="Background" Value="{StaticResource CueBannerBrush}" />                        </Trigger>                        <Trigger Property="Text" Value="{x:Null}">                            <Setter Property="Background" Value="{StaticResource CueBannerBrush}" />                        </Trigger>                          <Trigger Property="IsKeyboardFocused" Value="True">                            <Setter Property="Background" Value="White" />                            <Setter Property="Template">                                <Setter.Value>                                    <ControlTemplate TargetType="{x:Type TextBox}">                                        <Border x:Name="border" Width="Auto" Height="Auto" BorderThickness="1" BorderBrush="#FF7F9DB9">                                            <Grid x:Name="grid" Background="#FFFFFF">                                                <ScrollViewer VerticalAlignment="Center" HorizontalAlignment="Left"/>                                            </Grid>                                        </Border>                                    </ControlTemplate>                                </Setter.Value>                            </Setter>                        </Trigger>                    </Style.Triggers>                </Style>            </TextBox.Style>        </TextBox>

2. 在code behind 控制它失去焦点且值不为null 或者 empty的style

    <Style x:Key="CenterTextStyle" TargetType="{x:Type TextBox}">        <Setter Property="Template">            <Setter.Value>                <ControlTemplate TargetType="{x:Type TextBox}">                    <Border x:Name="border" Width="Auto" Height="Auto" BorderThickness="1" BorderBrush="#FF7F9DB9">                        <Grid x:Name="grid" Background="#FFFFFF">                            <ScrollViewer x:Name="PART_ContentHost" VerticalAlignment="Center" HorizontalAlignment="Left"/>                        </Grid>                    </Border>                </ControlTemplate>            </Setter.Value>        </Setter>    </Style>

Code behind：

      this.UserNameBox.LostFocus += UserNameBox_LostFocus;        private void UserNameBox_LostFocus(object sender, RoutedEventArgs e)        {            if (!string.IsNullOrWhiteSpace(this.UserNameBox.Text))            {                this.UserNameBox.Style = (Style)Application.Current.Resources["CenterTextStyle"];            }        }

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