WPF箭头图形添加文本失败求助：仅显示箭头，注释箭头后文本可见

Hey Benny, let's break down why your text isn't showing up with the arrow, and fix it step by step!

What's Going Wrong? #

The main issue here is likely incorrect text positioning combined with how WPF handles FormattedText coordinates. Let me explain:

• WPF's FormattedText.BuildGeometry() uses the bottom-left corner of the text as its starting point, not the top-left. Right now you're placing the text at (20, 5), which means the bottom of your 12pt text sits at Y=5—most of the text would be above that, outside the visible area of your arrow's bounds.
• While your drawing order (arrow first, text second) is correct (later items in a DrawingGroup draw on top), the text's off-screen position makes it invisible even when the arrow is there.

Fixes to Try #

1. Correct the Text's Starting Position

Calculate the Y-coordinate so the text sits vertically centered inside the arrow's shaft:

// Get the text's height and center it relative to the arrow's vertical center
double textY = centerY - formattedText.Height / 2;
Geometry textGeometry = formattedText.BuildGeometry(new System.Windows.Point(20, textY));

This will place the text's bottom-left corner at a position that keeps the entire text block within the arrow's shaft (between Y=50 and Y=150 in your current setup).

2. Optional: Adjust DrawingBrush Behavior

If you're using this DrawingBrush as a control background, the default Stretch=Fill might distort your arrow and text. Set it to maintain proportions:

var brush = new DrawingBrush(drawingGroup)
{
    Stretch = Stretch.Uniform,
    AlignmentX = AlignmentX.Left,
    AlignmentY = AlignmentY.Center
};

Full Corrected Code Snippet #

int Width = 200; int Length = 1000; 
double arrowHeadWidth = Width; 
double arrowHeadLength = Width / 2; 
double arrowWidth = Width - arrowHeadWidth / 2; 
double arrowLength = Length; 
double centerY = Width / 2.0; 

var figure = new PathFigure { IsClosed = true, StartPoint = new Point(0, centerY - arrowWidth / 2.0) }; 
figure.Segments.Add(new LineSegment(new Point(arrowLength - arrowHeadLength, centerY - arrowWidth / 2.0), true)); 
figure.Segments.Add(new LineSegment(new Point(arrowLength - arrowHeadLength, centerY - arrowHeadWidth / 2.0), true)); 
figure.Segments.Add(new LineSegment(new Point(arrowLength, centerY), true)); 
figure.Segments.Add(new LineSegment(new Point(arrowLength - arrowHeadLength, centerY + arrowHeadWidth / 2.0), true)); 
figure.Segments.Add(new LineSegment(new Point(arrowLength - arrowHeadLength, centerY + arrowWidth / 2.0), true)); 
figure.Segments.Add(new LineSegment(new Point(0, centerY + arrowWidth / 2.0), true)); 

var geometry = new PathGeometry(); 
geometry.Figures.Add(figure); 

var borderPen = new Pen(Brushes.White, 10) { LineJoin = PenLineJoin.Round }; 
var arrowDrawing = new GeometryDrawing(Brushes.Transparent, borderPen, geometry); 

FormattedText formattedText = new FormattedText( 
    "Test", 
    System.Globalization.CultureInfo.CurrentUICulture, 
    FlowDirection.LeftToRight, 
    new Typeface("Tahoma"), 
    12, 
    Brushes.Black); 
formattedText.MaxTextWidth = arrowLength - 40; 
formattedText.MaxTextHeight = arrowWidth - 10; 

// Fix text position to center vertically in the arrow shaft
double textY = centerY - formattedText.Height / 2;
Geometry textGeometry = formattedText.BuildGeometry(new System.Windows.Point(20, textY)); 

GeometryDrawing textDrawing = new GeometryDrawing(Brushes.Red, new Pen(Brushes.Red, 1), textGeometry); 

var drawingGroup = new DrawingGroup(); 
drawingGroup.Children.Add(arrowDrawing); 
drawingGroup.Children.Add(textDrawing); 

// Optional: Preserve aspect ratio when using the brush
var brush = new DrawingBrush(drawingGroup)
{
    Stretch = Stretch.Uniform,
    AlignmentX = AlignmentX.Left,
    AlignmentY = AlignmentY.Center
};

Give this a try—your text should now show up neatly inside the arrow's shaft!

内容的提问来源于stack exchange，提问作者Benny