AvaloniaUI/Avalonia · error · ArgumentOutOfRangeException

Parameter must be greater than or equal to zero.

Error message

Parameter must be greater than or equal to zero.

What it means

FormattedText.LineHeight setter rejects negative values because a negative line height makes line-breaking math produce overlapping or negative rectangles and breaks cursor/hit-testing. Zero is allowed (meaning the default line height).

Source

Thrown at src/Avalonia.Base/Media/FormattedText.cs:1061

                InvalidateMetrics();
            }
            get
            {
                return _defaultParaProps.TextAlignment;
            }
        }

        /// <summary>
        /// Gets or sets the height of, or the spacing between, each line where
        /// zero represents the default line height.
        /// </summary>
        public double LineHeight
        {
            set
            {
                if (value < 0)
                {
                    throw new ArgumentOutOfRangeException(nameof(value), "Parameter must be greater than or equal to zero.");
                }

                _defaultParaProps.SetLineHeight(value);

                InvalidateMetrics();
            }
            get
            {
                return _defaultParaProps.LineHeight;
            }
        }

        /// <summary>
        /// The MaxTextWidth property defines the alignment edges for the FormattedText.
        /// For example, left aligned text is wrapped such that the leftmost glyph alignment point
        /// on each line falls exactly on the left edge of the rectangle.
        /// Note that for many fonts, especially in italic style, some glyph strokes may extend beyond the edges of the alignment rectangle.
        /// For this reason, it is recommended that clients draw text with at least 1/6 em (i.e of the font size) unused margin space either side.

View on GitHub (pinned to 11c5427268)

Solutions

1. Clamp the value to [0, +Inf) before setting: value = Math.Max(0, value).
2. Use 0 to mean 'default' rather than a negative sentinel.
3. Constrain the input source (slider Minimum=0, numeric input validator).
4. Add an IValueConverter that coerces negative bound values to 0.

Example fix

// before
ft.LineHeight = requested; // requested may be -1 sentinel

// after
ft.LineHeight = requested < 0 ? 0 : requested;

double lh = double.IsFinite(value) ? Math.Max(0, value) : 0;
ft.LineHeight = lh;

When it happens

Trigger: Binding LineHeight to a Slider with Minimum < 0; reading LineHeight from a config file where the sign was mis-entered; computing LineHeight as a multiplier that can go negative (e.g. baseHeight * -1).

Common situations: User-customizable line spacing UI without a non-negative constraint; defaulting a nullable double to -1 as a sentinel and forgetting to map it to null/0 before setting LineHeight.

Related errors

• 'MaxTextHeight' property value must be greater than zero.
• The parameter value must be greater than zero.
• The parameter value cannot be greater than '{MaxFontEmSize}'
• The parameter value must be a number.
• 'MaxTextHeight' property value cannot be NaN.

AI-assisted analysis of AvaloniaUI/Avalonia@11c5427268 (2026-08-13). Data as JSON: /api/errors/53725acd92267b4a. Report an issue: GitHub.