Question

我有一个WPF ListView（GridView），单元格模板包含TextBlock。如果我在TextTrimming="CharacterEllipsis" TextWrapping="NoWrap"上添加：TextBlock，当列小于字符串的长度时，省略号将出现在字符串的末尾。我需要的是在字符串的开头加上省略号。

即。如果我有字符串Hello World!，我希望...lo World!代替Hello W...。

有什么想法吗？

Answer 1

我遇到了同样的问题并编写了一个附加属性来解决这个问题（或者说，提供此功能）。在这里捐赠我的代码：

USAGE

<controls:TextBlockTrimmer EllipsisPosition="Start">
    <TextBlock Text="Excuse me but can I be you for a while"
               TextTrimming="CharacterEllipsis" />
</controls:TextBlockTrimmer>

不要忘记在Page / Window / UserControl根目录中添加名称空间声明：

xmlns:controls="clr-namespace:Hillinworks.Wpf.Controls"

TextBlockTrimmer.EllipsisPosition可以是Start，Middle（mac风格）或End。很确定你可以找出他们名字中的哪一个。

CODE

TextBlockTrimmer.cs

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Linq;
using System.Text;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Markup;

namespace Hillinworks.Wpf.Controls
{
    enum EllipsisPosition
    {
        Start,
        Middle,
        End
    }

    [DefaultProperty("Content")]
    [ContentProperty("Content")]
    internal class TextBlockTrimmer : ContentControl
    {
        private class TextChangedEventScreener : IDisposable
        {
            private readonly TextBlockTrimmer _textBlockTrimmer;

            public TextChangedEventScreener(TextBlockTrimmer textBlockTrimmer)
            {
                _textBlockTrimmer = textBlockTrimmer;
                s_textPropertyDescriptor.RemoveValueChanged(textBlockTrimmer.Content,
                                                            textBlockTrimmer.TextBlock_TextChanged);
            }

            public void Dispose()
            {
                s_textPropertyDescriptor.AddValueChanged(_textBlockTrimmer.Content,
                                                         _textBlockTrimmer.TextBlock_TextChanged);
            }
        }

        private static readonly DependencyPropertyDescriptor s_textPropertyDescriptor =
            DependencyPropertyDescriptor.FromProperty(TextBlock.TextProperty, typeof(TextBlock));

        private const string ELLIPSIS = "...";

        private static readonly Size s_inifinitySize = new Size(double.PositiveInfinity, double.PositiveInfinity);

        public EllipsisPosition EllipsisPosition
        {
            get { return (EllipsisPosition)GetValue(EllipsisPositionProperty); }
            set { SetValue(EllipsisPositionProperty, value); }
        }

        public static readonly DependencyProperty EllipsisPositionProperty =
            DependencyProperty.Register("EllipsisPosition",
                                        typeof(EllipsisPosition),
                                        typeof(TextBlockTrimmer),
                                        new PropertyMetadata(EllipsisPosition.End,
                                                             TextBlockTrimmer.OnEllipsisPositionChanged));

        private static void OnEllipsisPositionChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
        {
            ((TextBlockTrimmer)d).OnEllipsisPositionChanged((EllipsisPosition)e.OldValue,
                                                             (EllipsisPosition)e.NewValue);
        }

        private string _originalText;

        private Size _constraint;

        protected override void OnContentChanged(object oldContent, object newContent)
        {
            var oldTextBlock = oldContent as TextBlock;
            if (oldTextBlock != null)
            {
                s_textPropertyDescriptor.RemoveValueChanged(oldTextBlock, TextBlock_TextChanged);
            }

            if (newContent != null && !(newContent is TextBlock))
                // ReSharper disable once LocalizableElement
                throw new ArgumentException("TextBlockTrimmer access only TextBlock content", nameof(newContent));

            var newTextBlock = (TextBlock)newContent;
            if (newTextBlock != null)
            {
                s_textPropertyDescriptor.AddValueChanged(newTextBlock, TextBlock_TextChanged);
                _originalText = newTextBlock.Text;
            }
            else
                _originalText = null;

            base.OnContentChanged(oldContent, newContent);
        }


        private void TextBlock_TextChanged(object sender, EventArgs e)
        {
            _originalText = ((TextBlock)sender).Text;
            this.TrimText();
        }

        protected override Size MeasureOverride(Size constraint)
        {
            _constraint = constraint;
            return base.MeasureOverride(constraint);
        }

        protected override Size ArrangeOverride(Size arrangeBounds)
        {
            var result = base.ArrangeOverride(arrangeBounds);
            this.TrimText();
            return result;
        }

        private void OnEllipsisPositionChanged(EllipsisPosition oldValue, EllipsisPosition newValue)
        {
            this.TrimText();
        }

        private IDisposable BlockTextChangedEvent()
        {
            return new TextChangedEventScreener(this);
        }


        private static double MeasureString(TextBlock textBlock, string text)
        {
            textBlock.Text = text;
            textBlock.Measure(s_inifinitySize);
            return textBlock.DesiredSize.Width;
        }

        private void TrimText()
        {
            var textBlock = (TextBlock)this.Content;
            if (textBlock == null)
                return;

            if (DesignerProperties.GetIsInDesignMode(textBlock))
                return;


            var freeSize = _constraint.Width
                           - this.Padding.Left
                           - this.Padding.Right
                           - textBlock.Margin.Left
                           - textBlock.Margin.Right;

            // ReSharper disable once CompareOfFloatsByEqualityOperator
            if (freeSize <= 0)
                return;

            using (this.BlockTextChangedEvent())
            {
                // this actually sets textBlock's text back to its original value
                var desiredSize = TextBlockTrimmer.MeasureString(textBlock, _originalText);


                if (desiredSize <= freeSize)
                    return;

                var ellipsisSize = TextBlockTrimmer.MeasureString(textBlock, ELLIPSIS);
                freeSize -= ellipsisSize;
                var epsilon = ellipsisSize / 3;

                if (freeSize < epsilon)
                {
                    textBlock.Text = _originalText;
                    return;
                }

                var segments = new List<string>();

                var builder = new StringBuilder();

                switch (this.EllipsisPosition)
                {
                    case EllipsisPosition.End:
                        TextBlockTrimmer.TrimText(textBlock, _originalText, freeSize, segments, epsilon, false);
                        foreach (var segment in segments)
                            builder.Append(segment);
                        builder.Append(ELLIPSIS);
                        break;

                    case EllipsisPosition.Start:
                        TextBlockTrimmer.TrimText(textBlock, _originalText, freeSize, segments, epsilon, true);
                        builder.Append(ELLIPSIS);
                        foreach (var segment in ((IEnumerable<string>)segments).Reverse())
                            builder.Append(segment);
                        break;

                    case EllipsisPosition.Middle:
                        var textLength = _originalText.Length / 2;
                        var firstHalf = _originalText.Substring(0, textLength);
                        var secondHalf = _originalText.Substring(textLength);

                        freeSize /= 2;

                        TextBlockTrimmer.TrimText(textBlock, firstHalf, freeSize, segments, epsilon, false);
                        foreach (var segment in segments)
                            builder.Append(segment);
                        builder.Append(ELLIPSIS);

                        segments.Clear();

                        TextBlockTrimmer.TrimText(textBlock, secondHalf, freeSize, segments, epsilon, true);
                        foreach (var segment in ((IEnumerable<string>)segments).Reverse())
                            builder.Append(segment);
                        break;
                    default:
                        throw new NotSupportedException();
                }

                textBlock.Text = builder.ToString();
            }
        }


        private static void TrimText(TextBlock textBlock,
                                     string text,
                                     double size,
                                     ICollection<string> segments,
                                     double epsilon,
                                     bool reversed)
        {
            while (true)
            {
                if (text.Length == 1)
                {
                    var textSize = TextBlockTrimmer.MeasureString(textBlock, text);
                    if (textSize <= size)
                        segments.Add(text);

                    return;
                }

                var halfLength = Math.Max(1, text.Length / 2);
                var firstHalf = reversed ? text.Substring(halfLength) : text.Substring(0, halfLength);
                var remainingSize = size - TextBlockTrimmer.MeasureString(textBlock, firstHalf);
                if (remainingSize < 0)
                {
                    // only one character and it's still too large for the room, skip it
                    if (firstHalf.Length == 1)
                        return;

                    text = firstHalf;
                    continue;
                }

                segments.Add(firstHalf);

                if (remainingSize > epsilon)
                {
                    var secondHalf = reversed ? text.Substring(0, halfLength) : text.Substring(halfLength);
                    text = secondHalf;
                    size = remainingSize;
                    continue;
                }

                break;
            }
        }
    }
}

Answer 2

不幸的是，今天在WPF中这是不可能的，因为你可以看到from the documentation。

（我以前在微软的WPF上工作过，这是我们遗憾的一个功能 - 不确定它是否计划用于未来的版本）

Answer 3

我实现（复制）了上面的TextBlockTrimmer代码，它非常适合加载，但TextBlock.Text之后不会更新，如果绑定到更改的View Model属性。我发现有用的是

在TextBlockText中定义名为TextBlockTrimmer的DependencyProperty，类似于上面的EllipsisPosition属性，包括OnTextBlockTextChanged()方法。
在OnTextBlockTextChanged()方法中，在致电_originalText之前将newValue设为TrimText()。
将TextBlockText属性绑定到View Model属性（在下面的XAML中名为SomeText）

将TextBlock.Text属性绑定到XAML中的TextBlockTrimmer.TextBlockText属性：

<controls:TextBlockTrimmer EllipsisPosition="Middle" TextBlockText="{Binding SomeText, Mode=OneWay}"
    <TextBlock Text="{Binding TextBlockText, RelativeSource={RelativeSource Mode=FindAncestor, AncestorType={x:Type controls:TextBlockTrimmer}}}" HorizontalAlignment="Stretch"/>
</controls:TextBlockTrimmer>

如果我将TextBlockTrimmer.TextBlockText和TextBlock.Text绑定到SomeText（但这样做会让我感到烦恼），这也很有效。

Answer 4

您可以尝试使用ValueConverter（参见IValueConverter interface）来更改应自己在列表框中显示的字符串。也就是说，在Convert方法的实现中，您将测试字符串是否长于可用空间，然后将它们更改为...加上字符串的右侧。

Answer 5

以下是如何使用递归对数算法进行有效文本剪切的示例：

private static string ClipTextToWidth(
    TextBlock reference, string text, double maxWidth)
{
    var half = text.Substring(0, text.Length/2);

    if (half.Length > 0)
    {
        reference.Text = half;
        var actualWidth = reference.ActualWidth;

        if (actualWidth > maxWidth)
        {
            return ClipTextToWidth(reference, half, maxWidth);
        }

        return half + ClipTextToWidth(
            reference,
            text.Substring(half.Length, text.Length - half.Length),
            maxWidth - actualWidth);
    }
    return string.Empty;
}

假设您有一个名为TextBlock的{{1}}字段，并且您希望以给定的最大宽度剪切其中的文本，并附加省略号。以下方法调用textBlock来设置ClipTextToWidth字段的文本：

textBlock

希望有所帮助！

Answer 6

感谢您的帮助hillin 和 bcunning。
为了完整起见，此处的代码必须附加到 hillin 描述的 bcunning 代码中。

TextBlockTrimmer.cs

public string TextBlockText
{
  get => (string)GetValue(TextBlockTextProperty);
  set => SetValue(TextBlockTextProperty, value);
}

public static readonly DependencyProperty TextBlockTextProperty =
  DependencyProperty.Register("TextBlockText",
                              typeof(string),
                              typeof(TextBlockTrimmer),
                              new PropertyMetadata("", OnTextBlockTextChanged));

private static void OnTextBlockTextChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
{
  ((TextBlockTrimmer)d).OnTextBlockTextChanged((string)e.OldValue, (string)e.NewValue);
}

private void OnTextBlockTextChanged(string oldValue, string newValue)
{
  _originalText = newValue;
  this.TrimText();
}

我在 ComboBox 中使用它，对我来说它是这样工作的。
XAML：

<ComboBox ItemsSource="{Binding MyPaths}" SelectedItem="{Binding SelectedPath}" ToolTip="{Binding SelectedPath}">
  <ComboBox.ItemTemplate>
    <DataTemplate>
      <controls:TextBlockTrimmer EllipsisPosition="Start" TextBlockText="{Binding Mode=OneWay}">
        <TextBlock Text="{Binding}" ToolTip="{Binding}"/>
      </controls:TextBlockTrimmer>
    </DataTemplate>
  </ComboBox.ItemTemplate>
</ComboBox>

Answer 7

如果其他人像我一样偶然发现了这个问题，那么这是另一个有更好答案的帖子（不记得）：

Auto clip and append dots in WPF label

在WPF ListView中字符串开头的省略号

7 个答案:

USAGE

CODE

TextBlockTrimmer.cs