c#筆記--WPF文本框和密碼框添加水印效果(背景文字提示)

文本框(TextBox)水印效果

顯示效果：

唯一原文鏈接：https://www.cnblogs.com/kongw/p/10744060.html

方法一:驗證觸發器填充VisualBrush

創建一個可視畫刷VisualBrush，使用觸發器驗證一下Text是否為空，使用VisualBrush填充TextBox的背景色

<TextBox Height="25" Width="180" HorizontalAlignment="Center" Margin="0 50 0 0">
    <TextBox.Resources>
        <VisualBrush x:Key="HelpBrush" TileMode="None" Opacity="0.3" Stretch="None" AlignmentX="Left">
            <VisualBrush.Visual>
                <TextBlock Text="請輸入賬號"/>
            </VisualBrush.Visual>
        </VisualBrush>
    </TextBox.Resources>
    <TextBox.Style>
        <Style TargetType="TextBox">
            <Style.Triggers>
                <Trigger Property="Text" Value="">
                    <Setter Property="Background" Value="{StaticResource HelpBrush}"/>
                </Trigger>
            </Style.Triggers>
        </Style>
    </TextBox.Style>
</TextBox>

方法二:判斷鼠標焦點填充SolidColorBrush

判斷TextBox獲取到焦點時文字消失，失去焦點時文字顯示，在后台使用SolidColorBrush畫刷填充
XAML代碼(添加TextBox獲取到焦點和失去焦點的事件)：

<TextBox Name="tbxUser" GotFocus="TbxUser_GotFocus" Foreground="LightGray" LostFocus="TbxUser_LostFocus"
         Height="25" Width="180" HorizontalAlignment="Center" Margin="0 20 0 0"></TextBox>

后台代碼(由於窗口剛加載時沒有判斷焦點，所以在窗口加載時初始化填充，然后判斷捕捉到鼠標焦點時取消填充，失去焦點時判斷是否輸入了文字，沒輸入則再次填充)：

public MainWindow()
{
    InitializeComponent();
    tbxUser.Text = "請輸入賬號";
    SolidColorBrush scb = new SolidColorBrush(Colors.LightGray);
    tbxUser.Foreground = scb;
}
private void TbxUser_GotFocus(object sender, RoutedEventArgs e)
{
    tbxUser.Text = "";
    SolidColorBrush scb = new SolidColorBrush(Colors.Black);
    tbxUser.Foreground = scb;
}

private void TbxUser_LostFocus(object sender, RoutedEventArgs e)
{
    if (string.IsNullOrEmpty(tbxUser.Text))
    {
        tbxUser.Text = "請輸入賬號";
        SolidColorBrush scb = new SolidColorBrush(Colors.LightGray);
        tbxUser.Foreground = scb;
    }
}

兩種方法的區別在於第一種鼠標點擊TextBox時提示文字不會消失，當輸入文字時才消失，第二種方法則是鼠標點擊TextBox時則提示文字消失

密碼框(PasswordBox)水印效果

顯示效果：

由於密碼框沒有可以用於判斷輸入值非空的依賴屬性，於是我們添加一個PasswordBoxMonitor類來監測密碼框是否為空，繼承與DependencyObject類；通過PasswordLength屬性來判斷密碼框輸入的內容長度是否為0來顯示水印
需要引入的命名空間：

using System.Windows;
using System.Windows.Controls;

PasswordBoxMonitor類代碼：

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(0));

    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);
    }
}

創建好類之后再使用重構的PasswordBox，需要在window中引用

xmlns:PasswordStyle="clr-namespace:你的項目名"

之后在PasswordBox樣式中重寫ControlTemplate 方法，添加一個TextBox覆蓋掉密碼框，當輸入文字之后隱藏掉TextBox
XAML代碼：

<PasswordBox VerticalAlignment="Center" Name="pb" HorizontalAlignment="Center"  
             VerticalContentAlignment="Center" Height="30"  Width="220"
             Margin="0 10 0 0">
        <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="PasswordStyle: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=" 請輸入密碼"/>
                                </StackPanel>
                            </Grid>
                        </Border>
                        <ControlTemplate.Triggers>
                            <Trigger Property="IsEnabled" Value="false">
                                <Setter Property="Visibility" TargetName="myStackPanel" Value="Collapsed"/>
                            </Trigger>
                            <Trigger Property="PasswordStyle:PasswordBoxMonitor.PasswordLength" Value="0">
                                <Setter Property="Visibility" TargetName="myStackPanel" Value="Visible"/>
                            </Trigger>
                        </ControlTemplate.Triggers>
                    </ControlTemplate>
                </Setter.Value>
            </Setter>
        </Style>
    </PasswordBox.Style>
</PasswordBox>

提示：寫完之后可能會提示命名空間找不到，有時候是編譯器沒刷新過來，嘗試編譯運行一下就好了
♪(＾∀＾●)ﾉ