WPF使用TextBlock实现查找结果高亮显示

阅读原文时间：2023年08月28日阅读：1

在应用开发过程中，经常遇到这样的需求：通过关键字查找数据，把带有关键字的数据显示出来，同时在结果中高亮显示关键字。在web开发中，只需在关键字上加一层标签，然后设置标签样式就可以轻松实现。

在WPF中显示文本内容通常采用TextBlock控件，也可以采用类似的方式，通过内联流内容元素Run达到同样的效果：

<TextBlock FontSize="20">
    <Run Text="Hel" /><Run Foreground="Red" Text="lo " /><Run Text="Word" />
</TextBlock>

需要注意的是每个Run之间不要换行，如果换行的话，每个Run之间会有间隙，看起来像增加了空格。

通过这种方式实现查找结果中高亮关键字，需要把查找结果拆分成三部分，然后绑定到Run元素的Text属性，或者在后台代码中使用TextBlock的Inlines属性添加Run元素

textBlock1.Inlines.Add(new Run("hel"));
textBlock1.Inlines.Add(new Run("lo ") { Foreground=new SolidColorBrush(Colors.Red)});
textBlock1.Inlines.Add(new Run("world"));

这种方法虽然可以达到效果，但显然与MVVM的思想不符。接下来本文介绍一种通过附加属性实现TextBlock中指定内容高亮。

技术要点与实现

通过TextEffect的PositionStart、PositionCount以及Foreground属性设置字符串中需要高亮内容的起始位置、长度以及高亮颜色。定义附加属性允许TextBlock设置需要高亮的内容位置以及颜色。

首先定义类ColoredLettering(并不要求继承DependencyObject)。
在ColoredLettering中注册自定义的附加属性，注册附加属性方式与注册依赖属性类似，不过附加属性是用DependencyProperty.RegisterAttached来注册。

给附加属性注册属性值变化事件，事件处理逻辑中设置TextEffect的PositionStart、PositionCount以及Foreground实现内容高亮。

public class ColoredLettering
{
public static void SetColorStart(TextBlock textElement, int value)
{
textElement.SetValue(ColorStartProperty, value);
}

public static int GetColorStart(TextBlock textElement)
{
    return (int)textElement.GetValue(ColorStartProperty);
}

// Using a DependencyProperty as the backing store for ColorStart.  This enables animation, styling, binding, etc...
public static readonly DependencyProperty ColorStartProperty =
    DependencyProperty.RegisterAttached("ColorStart", typeof(int), typeof(ColoredLettering), new FrameworkPropertyMetadata(0, OnColorStartChanged));

private static void OnColorStartChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
{
    TextBlock textBlock = d as TextBlock;
    if (textBlock != null)
    {
        if (e.NewValue == e.OldValue) return;
            if (e.NewValue is int)
            {
                int count = GetColorLength(textBlock);
                Brush brush = GetForeColor(textBlock);
                if ((int)e.NewValue <= 0 || count <= 0 || brush == TextBlock.ForegroundProperty.DefaultMetadata.DefaultValue) return;
                if (textBlock.TextEffects.Count != 0)
                {
                    textBlock.TextEffects.Clear();
                }
                TextEffect textEffect = new TextEffect()
                {
                    Foreground = brush,
                    PositionStart = (int)e.NewValue,
                    PositionCount = count
                };
                textBlock.TextEffects.Add(textEffect);
            }
    }
}

public static void SetColorLength(TextBlock textElement, int value)
{
    textElement.SetValue(ColorLengthProperty, value);
}

public static int GetColorLength(TextBlock textElement)
{
    return (int)textElement.GetValue(ColorLengthProperty);
}

// Using a DependencyProperty as the backing store for ColorStart.  This enables animation, styling, binding, etc...
public static readonly DependencyProperty ColorLengthProperty =
    DependencyProperty.RegisterAttached("ColorLength", typeof(int), typeof(ColoredLettering), new FrameworkPropertyMetadata(0, OnColorLengthChanged));

private static void OnColorLengthChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
{
    TextBlock textBlock = d as TextBlock;
        if (textBlock != null)
        {
            if (e.NewValue == e.OldValue) return;
            if (e.NewValue is int)
            {
                int start = GetColorStart(textBlock);
                Brush brush = GetForeColor(textBlock);
                if ((int)e.NewValue <= 0 || start <= 0 || brush == TextBlock.ForegroundProperty.DefaultMetadata.DefaultValue) return;
                if (textBlock.TextEffects.Count != 0)
                {
                    textBlock.TextEffects.Clear();
                }
                TextEffect textEffect = new TextEffect()
                {
                    Foreground = brush,
                    PositionStart = start,
                    PositionCount = (int)e.NewValue
                };
                textBlock.TextEffects.Add(textEffect);
            }
        }
}

public static void SetForeColor(TextBlock textElement, Brush value)
{
    textElement.SetValue(ColorStartProperty, value);
}

public static Brush GetForeColor(TextBlock textElement)
{
    return (Brush)textElement.GetValue(ForeColorProperty);
}

// Using a DependencyProperty as the backing store for ForeColor.  This enables animation, styling, binding, etc...
public static readonly DependencyProperty ForeColorProperty =
    DependencyProperty.RegisterAttached("ForeColor", typeof(Brush), typeof(ColoredLettering), new PropertyMetadata(TextBlock.ForegroundProperty.DefaultMetadata.DefaultValue, OnForeColorChanged));

private static void OnForeColorChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
{
    TextBlock textBlock = d as TextBlock;
    if (textBlock != null)
    {
        if (e.NewValue == e.OldValue) return;
        if (e.NewValue is Brush)
        {
            int start = GetColorStart(textBlock);
            int count = GetColorLength(textBlock);
            if (start <= 0 || count <= 0) return;
            if (textBlock.TextEffects.Count != 0)
            {
                textBlock.TextEffects.Clear();
            }
            TextEffect textEffect = new TextEffect()
            {
                Foreground = (Brush)e.NewValue,
                PositionStart = start,
                PositionCount = count
            };
            textBlock.TextEffects.Add(textEffect);
        }
    }
}

}

调用时只需在TextBlock指定需要高亮内容的开始位置，内容长度以及高亮颜色即可。

<TextBlock local:ColoredLettering.ColorLength="{Binding Count}"
           local:ColoredLettering.ColorStart="{Binding Start}"
           local:ColoredLettering.ForeColor="{Binding ForeColor}"
           FontSize="20"
           Text="Hello World" />