Make a class called TextBlockTrimmer and write the following.
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;
}
}
}
Then use it as follows:
<local:TextBlockTrimmer EllipsisPosition="Start" Grid.Column="0">
<TextBlock Text="Excuse me but can I be you for a while"
TextTrimming="CharacterEllipsis" />
</local:TextBlockTrimmer>
Taken from here
