根据TextWrapping属性获取TextBlock的行数？

Question

我在 WPF 应用程序中有一个 TextBlock。

TextBlock 的 (Text, Width, Height, TextWrapping, FontSize, FontWeight, FontFamily) 属性是动态的（由用户在运行时输入） .

每次用户更改之前的属性之一时，TextBlock 的 Content 属性都会在运行时更改。 （到这里一切都好）

现在，我需要根据之前指定的属性来获取TextBlock 的行。
这意味着我需要TextWrapping 算法将产生的行。

换句话说，我需要将每一行放在一个单独的字符串中，或​​者我需要一个带有 Scape Sequence \n 的字符串。

有什么想法吗？

Answer 1

如果没有公开的方式来做到这一点，我会感到惊讶（尽管永远不知道，尤其是使用 WPF）。
确实看起来TextPointer class 是我们的朋友，所以这里有一个基于TextBlock.ContentStart、TextPointer.GetLineStartPosition 和TextPointer.GetOffsetToPosition 的解决方案：

public static class TextUtils
{
    public static IEnumerable<string> GetLines(this TextBlock source)
    {
        var text = source.Text;
        int offset = 0;
        TextPointer lineStart = source.ContentStart.GetPositionAtOffset(1, LogicalDirection.Forward);
        do
        {
            TextPointer lineEnd = lineStart != null ? lineStart.GetLineStartPosition(1) : null;
            int length = lineEnd != null ? lineStart.GetOffsetToPosition(lineEnd) : text.Length - offset;
            yield return text.Substring(offset, length);
            offset += length;
            lineStart = lineEnd;
        }
        while (lineStart != null);
    }
}

这里不多解释
获取行的起始位置，减去上一行的起始位置得到行文本的长度，我们就到这里了。
唯一棘手（或不明显）的部分是需要将ContentStart 偏移一个，因为设计The TextPointer returned by this property always has its LogicalDirection set to Backward.，所以我们需要获取相同的指针（！？ ) 位置，但使用 LogicalDirection set to Forward，不管这意味着什么。

Answer 2

使用FormattedText 类，可以首先创建格式化文本并评估其大小，因此您知道第一步所占用的空间， 如果太长，则由您决定分成几行。

然后在第二步中，它可以被绘制。

DrawingContext 对象上的一切都可能发生在以下方法中：

protected override void OnRender(System.Windows.Media.DrawingContext dc)

这里是 CustomControl 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();

            // put clip for preventing writing out the textblock
            drawingContext.PushClip(new RectangleGeometry(new Rect(new Point(0, 0), new Point(ActualWidth, ActualHeight))));
            FormattedText formattedText = null;

            // have an initial guess :
            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))
            {
                // Add 15%
                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（此处的边框显示有效剪辑）：

<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, &quot;and what is the use of a book,&quot; thought Alice, ...</local:TextBlockLineSplitter>
</Border>

Answer 3

如果没有问题，您可以在 TextBlock 控件上使用反射（它当然知道字符串是如何包装的）。如果你不使用 MVVM，我想它适合你。

首先，我创建了一个最小的窗口来测试我的解决方案：

<Window x:Class="WpfApplication1.MainWindow" Name="win"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="MainWindow" Height="600" Width="600">

    <StackPanel>
        <TextBlock Name="txt"  Text="Lorem ipsum dolor sit amet, consectetur adipisci elit, sed eiusmod tempor incidunt ut labore et dolore magna aliqua." Margin="20" 
                   TextWrapping="Wrap" />
        <Button Click="OnCalculateClick" Content="Calculate ROWS" Margin="5" />

        <TextBox Name="Result" Height="100" />
    </StackPanel>

</Window>

现在让我们看看代码隐藏中最重要的部分：

private void OnCalculateClick(object sender, EventArgs args)
{
    int start = 0;
    int length = 0;

    List<string> tokens = new List<string>();

    foreach (object lineMetrics in GetLineMetrics(txt))
    {
        length = GetLength(lineMetrics);
        tokens.Add(txt.Text.Substring(start, length));

        start += length;
    }

    Result.Text = String.Join(Environment.NewLine, tokens);
}

private int GetLength(object lineMetrics)
{
    PropertyInfo propertyInfo = lineMetrics.GetType().GetProperty("Length", BindingFlags.Instance
        | BindingFlags.NonPublic);

    return (int)propertyInfo.GetValue(lineMetrics, null);
}

private IEnumerable GetLineMetrics(TextBlock textBlock)
{
    ArrayList metrics = new ArrayList();
    FieldInfo fieldInfo = typeof(TextBlock).GetField("_firstLine", BindingFlags.Instance
        | BindingFlags.NonPublic);
    metrics.Add(fieldInfo.GetValue(textBlock));

    fieldInfo = typeof(TextBlock).GetField("_subsequentLines", BindingFlags.Instance
        | BindingFlags.NonPublic);

    object nextLines = fieldInfo.GetValue(textBlock);
    if (nextLines != null)
    {
        metrics.AddRange((ICollection)nextLines);
    }

    return metrics;
}

GetLineMetrics 方法检索 LineMetrics 的集合（一个内部对象，所以我不能直接使用它）。该对象有一个名为“Length”的属性，其中包含您需要的信息。所以GetLength 方法只是读取这个属性的值。

行存储在名为tokens 的列表中，并使用TextBox 控件显示（只是为了获得即时反馈）。

我希望我的示例可以帮助您完成任务。