I need a reliable method to get the height of the text contained in a RichTextBlock, even before it is actually drawn on the scene.
Using the normal Measure() method produces a weird result, as it can be seen in the MVCE: https://github.com/cghersi/UWPExamples/tree/master/MeasureText (I want to keep fiexed the width, and measure the final height, but the result of DesiredSize is far different from the actual height!!).
For this reason, I found a rough method (mentioned here https://stackoverflow.com/a/45937298/919700), that I extended to serve my purpose, where we use some Win2D API to compute the content height.
The problem is that in some cases, this method provides an height that is smaller than the expected one.
- Is there a general way to retrieve the (correct) height of a TextBlock, even before it is drawn on the scene?
- If this is not the case, what am I doing wrong?
Here's my code (which you can find also as MVCE here: https://github.com/cghersi/UWPExamples/tree/master/RichText):
public sealed partial class MainPage
{
public static readonly FontFamily FONT_FAMILY = new FontFamily("Assets/paltn.ttf#Palatino-Roman");
public const int FONT_SIZE = 10;
private readonly Dictionary<string, object> FONT = new Dictionary<string, object>
{
{ AttrString.FONT_FAMILY_KEY, FONT_FAMILY },
{ AttrString.FONT_SIZE_KEY, FONT_SIZE },
{ AttrString.LINE_HEAD_INDENT_KEY, 10 },
{ AttrString.LINE_SPACING_KEY, 1.08 },
{ AttrString.FOREGROUND_COLOR_KEY, new SolidColorBrush(Colors.Black) }
};
// ReSharper disable once PrivateFieldCanBeConvertedToLocalVariable
private readonly RichTextBlock m_displayedText;
public MainPage()
{
InitializeComponent();
// create the text block:
m_displayedText = new RichTextBlock
{
MaxLines = 0, //Let it use as many lines as it wants
TextWrapping = TextWrapping.Wrap,
AllowFocusOnInteraction = false,
IsHitTestVisible = false,
Width = 80,
Height = 30,
Margin = new Thickness(100)
};
// set the content with the right properties:
AttrString content = new AttrString("Excerpt1 InkLink", FONT);
SetRichText(m_displayedText, content);
// add to the main panel:
MainPanel.Children.Add(m_displayedText);
// compute the text height: (this gives the wrong answer!!):
double textH = GetRichTextHeight(content, (float)m_displayedText.Width);
Console.WriteLine("text height: {0}", textH);
}
public static double GetRichTextHeight(AttrString text, float maxWidth)
{
if (text == null)
return 0;
CanvasDevice device = CanvasDevice.GetSharedDevice();
double finalH = 0;
foreach (AttributedToken textToken in text.Tokens)
{
CanvasTextFormat frmt = new CanvasTextFormat()
{
Direction = CanvasTextDirection.LeftToRightThenTopToBottom,
FontFamily = textToken.Get(AttrString.FONT_FAMILY_KEY, FONT_FAMILY).Source,
FontSize = textToken.Get(AttrString.FONT_SIZE_KEY, FONT_SIZE),
WordWrapping = CanvasWordWrapping.Wrap
};
CanvasTextLayout layout = new CanvasTextLayout(device, textToken.Text, frmt, maxWidth, 0f);
finalH += layout.LayoutBounds.Height;
}
return finalH;
//return textBlock.Blocks.Sum(block => block.LineHeight);
}
private static void SetRichText(RichTextBlock label, AttrString str)
{
if ((str == null) || (label == null))
return;
label.Blocks.Clear();
foreach (AttributedToken token in str.Tokens)
{
Paragraph paragraph = new Paragraph()
{
TextAlignment = token.Get(AttrString.TEXT_ALIGN_KEY, TextAlignment.Left),
TextIndent = token.Get(AttrString.LINE_HEAD_INDENT_KEY, 0),
};
double fontSize = token.Get(AttrString.FONT_SIZE_KEY, FONT_SIZE);
double lineSpacing = token.Get(AttrString.LINE_SPACING_KEY, 1.0);
paragraph.LineHeight = fontSize * lineSpacing;
paragraph.LineStackingStrategy = LineStackingStrategy.BlockLineHeight;
Run run = new Run
{
Text = token.Text,
FontFamily = token.Get(AttrString.FONT_FAMILY_KEY, FONT_FAMILY),
FontSize = fontSize,
Foreground = token.Get(AttrString.FOREGROUND_COLOR_KEY, new SolidColorBrush(Colors.Black)),
FontStyle = token.Get(AttrString.ITALIC_KEY, false) ?
Windows.UI.Text.FontStyle.Italic : Windows.UI.Text.FontStyle.Normal
};
paragraph.Inlines.Add(run);
label.Blocks.Add(paragraph);
}
}
}
public class AttrString
{
public const string FONT_FAMILY_KEY = "Fam";
public const string FONT_SIZE_KEY = "Size";
public const string LINE_HEAD_INDENT_KEY = "LhI";
public const string LINE_SPACING_KEY = "LSpace";
public const string FOREGROUND_COLOR_KEY = "Color";
public const string ITALIC_KEY = "Ita";
public const string TEXT_ALIGN_KEY = "Align";
public const string LINE_BREAK_MODE_KEY = "LineBreak";
public static Dictionary<string, object> DefaultCitationFont { get; set; }
public static Dictionary<string, object> DefaultFont { get; set; }
public List<AttributedToken> Tokens { get; set; }
public AttrString(string text, Dictionary<string, object> attributes)
{
Tokens = new List<AttributedToken>();
Append(text, attributes);
}
public AttrString(AttrString copy)
{
if (copy?.Tokens == null)
return;
Tokens = new List<AttributedToken>(copy.Tokens);
}
public AttrString Append(string text, Dictionary<string, object> attributes)
{
Tokens.Add(new AttributedToken(text, attributes));
return this;
}
public bool IsEmpty()
{
foreach (AttributedToken t in Tokens)
{
if (!string.IsNullOrEmpty(t.Text))
return false;
}
return true;
}
public override string ToString()
{
StringBuilder sb = new StringBuilder();
foreach (AttributedToken t in Tokens)
{
sb.Append(t.Text);
}
return sb.ToString();
}
}
public class AttributedToken
{
public string Text { get; set; }
public Dictionary<string, object> Attributes { get; set; }
public AttributedToken(string text, Dictionary<string, object> attributes)
{
Text = text;
Attributes = attributes;
}
public T Get<T>(string key, T defaultValue)
{
if (string.IsNullOrEmpty(key) || (Attributes == null))
return defaultValue;
if (Attributes.ContainsKey(key))
return (T)Attributes[key];
else
return defaultValue;
}
public override string ToString()
{
return Text;
}
}
** UPDATE **:
After further digging into the issue, the problem seems related to the lack of configurability for the CanvasTextFormat object, especially for the indentation of the first line (expressed in the RichTextBlock using the property Paragraph.TextIndent). Is there any way to specify such setting in a CanvasTextFormat object?
