我有一个 WPF ListView (GridView) 并且单元格模板包含一个 TextBlock。如果我在TextBlock 上添加：TextTrimming="CharacterEllipsis" TextWrapping="NoWrap"，当列小于字符串长度时，我的字符串末尾会出现一个省略号。我需要的是在字符串的开头有省略号。
即如果我有字符串Hello World!，我想要...lo World!，而不是Hello W...。
有什么想法吗？
【问题讨论】：
标签： c# wpf string listview ellipsis
我遇到了同样的问题并写了一个附加属性来解决这个问题（或者说，提供这个功能）。在这里捐赠我的代码：
<controls:TextBlockTrimmer EllipsisPosition="Start">
<TextBlock Text="Excuse me but can I be you for a while"
TextTrimming="CharacterEllipsis" />
</controls:TextBlockTrimmer>
不要忘记在您的 Page/Window/UserControl 根目录中添加命名空间声明：
xmlns:controls="clr-namespace:Hillinworks.Wpf.Controls"
TextBlockTrimmer.EllipsisPosition 可以是Start、Middle（mac 样式）或End。很确定你可以从他们的名字中找出哪个是哪个。
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;
}
}
}
}
【讨论】：
我实现（复制）了上面的TextBlockTrimmer 代码，它非常适合加载，但如果绑定到更改的视图模型属性，TextBlock.Text 之后不会更新。
我发现有效的是
TextBlockTrimmer 中定义一个名为TextBlockText 的DependencyProperty，类似于上面的EllipsisPosition 属性，包括一个OnTextBlockTextChanged() 方法。OnTextBlockTextChanged() 方法中，在调用TrimText() 之前将_originalText 设置为newValue。TextBlockText 属性绑定到视图模型属性（在下面的XAML 中称为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，它也可以工作（但这样做让我很烦）。
【讨论】：
不幸的是，这在今天的 WPF 中是不可能的，你可以看到from the documentation。
（我曾在 Microsoft 从事 WPF 工作，很遗憾，这是我们没有去做的一项功能——不确定是否计划在未来的版本中使用）
【讨论】：
您可以尝试使用 ValueConverter (cf.IValueConverter interface) 自己更改应该在列表框中显示的字符串。 也就是说，在 Convert 方法的实现中，你会测试字符串是否比可用空间长，然后将它们更改为 ... 加上字符串的右侧。
【讨论】：
这是一个如何使用递归对数算法进行高效文本剪辑的示例：
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TextBlock 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ClipTextToWidth 为textBlock 字段设置文本：
public void UpdateTextBlock(string text, double maxWidth)
{
if (text != null)
{
this.textBlock.Text = text;
if (this.textBlock.ActualWidth > maxWidth)
{
this.textBlock.Text = "...";
var ellipsisWidth = this.textBlock.ActualWidth;
this.textBlock.Text = "..." + ClipTextToWidth(
this.textBlock, text, maxWidth - ellipsisWidth);
}
}
else
{
this.textBlock.Text = string.Empty;
}
}
希望有帮助！
【讨论】：
感谢您的帮助 hillin 和 bcunning。
为完整起见，这里的代码必须附加到hillin 由bcunning 描述的代码中。
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>
【讨论】：
您可以使用IMultiValueConverter 自己修剪文本来实现这一点。
在转换方法中，您测试字符串长度，如果它比TextBlock.ActualWidth 长，则将其修剪。
这是我使用的实现：
public class StartTrimmingConverter :IMultiValueConverter
{
public object Convert(object[] values, Type targetType, object parameter,
CultureInfo culture)
{
if (values.Length != 2 || !(values[1] is TextBlock))
return string.Empty;
TextBlock reference = values[1] as TextBlock;
return GetTrimmedText(reference, values[0].ToString());
}
public object[] ConvertBack(object value, Type[] targetTypes, object parameter,
CultureInfo culture) => throw new NotImplementedException();
private static string GetTrimmedText(TextBlock reference, string text)
{
if (text != null)
{
double maxWidth = reference.ActualWidth -
reference.Padding.Left - reference.Padding.Right;
if (MeasureString(reference, text).Width > maxWidth)
{
double ellipsisWidth = MeasureString(reference, "...").Width;
return "..." + ClipTextToWidth(reference, text,
maxWidth - ellipsisWidth);
}
else
return text;
}
else
return string.Empty;
}
private static string ClipTextToWidth(TextBlock reference, string text,
double maxWidth)
{
int start = (int)Math.Ceiling(text.Length / 2.0f);
string half = text.Substring(start, text.Length / 2);
if (half.Length > 0)
{
double actualWidth = MeasureString(reference, half).Width;
if (MeasureString(reference, half).Width > maxWidth)
{
return ClipTextToWidth(reference, half, maxWidth);
}
return ClipTextToWidth(reference, text.Substring(0, start),
maxWidth - actualWidth) + half;
}
return string.Empty;
}
private static Size MeasureString(TextBlock reference, string candidate)
{
FormattedText formattedText = new FormattedText(
candidate,
CultureInfo.CurrentCulture,
FlowDirection.LeftToRight,
new Typeface(reference.FontFamily, reference.FontStyle,
reference.FontWeight, reference.FontStretch),
reference.FontSize,
Brushes.Black,
new NumberSubstitution(),
1);
return new Size(formattedText.Width, formattedText.Height);
}
}
对于 XAML 的使用：
<Resources>
<my:StartTrimmingConverter x:Key="trimConv" />
</Resources>
...
<TextBlock>
<TextBlock.Text>
<MultiBinding Converter="{StaticResource trimConv}">
<Binding Path="PropertyName"/>
<Binding RelativeSource="{RelativeSource Self}"/>
</MultiBinding>
</TextBlock.Text>
</TextBlock>
（感谢丹尼尔对文本剪切的递归对数算法的回答）
【讨论】：
如果其他人像我一样偶然发现这个问题，这里有另一个更好的答案（不计分）：
【讨论】：
TextTrimming="CharacterEllipsis"。