使用FormattedText类，可以先创建格式化文本并评估其大小，以便在第一步中确定它占用的空间，
如果太长，您可以将其拆分成单独的行。
然后在第二步中，可以绘制它。
所有操作都可以在以下方法的DrawingContext对象上完成：
protected override void OnRender(System.Windows.Media.DrawingContext dc)
这里是 自定义控件 解决方案:
[ContentProperty("Text")]
public class TextBlockLineSplitter : FrameworkElement
{
public FontWeight FontWeight
{
get { return (FontWeight)GetValue(FontWeightProperty); }
set { SetValue(FontWeightProperty, value); }
}
public static readonly DependencyProperty FontWeightProperty =
DependencyProperty.Register("FontWeight", typeof(FontWeight), typeof(TextBlockLineSplitter), new PropertyMetadata(FontWeight.FromOpenTypeWeight(400)));
public double FontSize
{
get { return (double)GetValue(FontSizeProperty); }
set { SetValue(FontSizeProperty, value); }
}
public static readonly DependencyProperty FontSizeProperty =
DependencyProperty.Register("FontSize", typeof(double), typeof(TextBlockLineSplitter), new PropertyMetadata(10.0));
public String FontFamily
{
get { return (String)GetValue(FontFamilyProperty); }
set { SetValue(FontFamilyProperty, value); }
}
public static readonly DependencyProperty FontFamilyProperty =
DependencyProperty.Register("FontFamily", typeof(String), typeof(TextBlockLineSplitter), new PropertyMetadata("Arial"));
public String Text
{
get { return (String)GetValue(TextProperty); }
set { SetValue(TextProperty, value); }
}
public static readonly DependencyProperty TextProperty =
DependencyProperty.Register("Text", typeof(String), typeof(TextBlockLineSplitter), new PropertyMetadata(null));
public double Interline
{
get { return (double)GetValue(InterlineProperty); }
set { SetValue(InterlineProperty, value); }
}
public static readonly DependencyProperty InterlineProperty =
DependencyProperty.Register("Interline", typeof(double), typeof(TextBlockLineSplitter), new PropertyMetadata(3.0));
public List<String> Lines
{
get { return (List<String>)GetValue(LinesProperty); }
set { SetValue(LinesProperty, value); }
}
public static readonly DependencyProperty LinesProperty =
DependencyProperty.Register("Lines", typeof(List<String>), typeof(TextBlockLineSplitter), new PropertyMetadata(new List<String>()));
protected override void OnRender(DrawingContext drawingContext)
{
base.OnRender(drawingContext);
Lines.Clear();
if (!String.IsNullOrWhiteSpace(Text))
{
string remainingText = Text;
string textToDisplay = Text;
double availableWidth = ActualWidth;
Point drawingPoint = new Point();
drawingContext.PushClip(new RectangleGeometry(new Rect(new Point(0, 0), new Point(ActualWidth, ActualHeight))));
FormattedText formattedText = null;
formattedText = new FormattedText(textToDisplay,
Thread.CurrentThread.CurrentUICulture,
FlowDirection.LeftToRight,
new Typeface(FontFamily),
FontSize,
Brushes.Black);
double estimatedNumberOfCharInLines = textToDisplay.Length * availableWidth / formattedText.Width;
while (!String.IsNullOrEmpty(remainingText))
{
double currentEstimatedNumberOfCharInLines = Math.Min(remainingText.Length, estimatedNumberOfCharInLines * 1.15);
do
{
textToDisplay = remainingText.Substring(0, (int)(currentEstimatedNumberOfCharInLines));
formattedText = new FormattedText(textToDisplay,
Thread.CurrentThread.CurrentUICulture,
FlowDirection.LeftToRight,
new Typeface(FontFamily),
FontSize,
Brushes.Black);
currentEstimatedNumberOfCharInLines -= 1;
} while (formattedText.Width > availableWidth);
Lines.Add(textToDisplay);
System.Diagnostics.Debug.WriteLine(textToDisplay);
System.Diagnostics.Debug.WriteLine(remainingText.Length);
drawingContext.DrawText(formattedText, drawingPoint);
if (remainingText.Length > textToDisplay.Length)
remainingText = remainingText.Substring(textToDisplay.Length);
else
remainingText = String.Empty;
drawingPoint.Y += formattedText.Height + Interline;
}
foreach (var line in Lines)
{
System.Diagnostics.Debug.WriteLine(line);
}
}
}
}
该控件的使用（边框在这里表示有效剪辑）：
<Border BorderThickness="1" BorderBrush="Red" Height="200" VerticalAlignment="Top">
<local:TextBlockLineSplitter>Alice was beginning to get very tired of sitting by her sister on the bank, and of having nothing to do. Once or twice she had peeped into the book her sister was reading, but it had no pictures or conversations in it, "
</Border>
