agrobot_base/AgroBase/OperationControl/Controls/AutoFitTextBlock.cs

using System;
using System.ComponentModel;
using System.Globalization;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Media;

namespace OperationControl.Controls
{
    public class AutoFitTextBlock : TextBlock
    {
        public static readonly DependencyProperty MinFontSizeProperty =
            DependencyProperty.Register(
                nameof(MinFontSize),
                typeof(double),
                typeof(AutoFitTextBlock),
                new PropertyMetadata(10.0, OnAutoFitPropertyChanged));

        public static readonly DependencyProperty MaxLinesProperty =
            DependencyProperty.Register(
                nameof(MaxLines),
                typeof(int),
                typeof(AutoFitTextBlock),
                new PropertyMetadata(2, OnAutoFitPropertyChanged));

        private double _baseFontSize = 14;
        private bool _isAdjusting;

        public double MinFontSize
        {
            get => (double)GetValue(MinFontSizeProperty);
            set => SetValue(MinFontSizeProperty, value);
        }

        public int MaxLines
        {
            get => (int)GetValue(MaxLinesProperty);
            set => SetValue(MaxLinesProperty, value);
        }

        public AutoFitTextBlock()
        {
            Loaded += AutoFitTextBlock_Loaded;
            SizeChanged += (_, _) => AdjustFontSize();
        }

        private void AutoFitTextBlock_Loaded(object sender, RoutedEventArgs e)
        {
            _baseFontSize = FontSize;

            WatchProperty(TextProperty);
            WatchProperty(FontSizeProperty);
            WatchProperty(FontFamilyProperty);
            WatchProperty(FontStyleProperty);
            WatchProperty(FontWeightProperty);
            WatchProperty(FontStretchProperty);
            WatchProperty(TextWrappingProperty);

            AdjustFontSize();
        }

        private void WatchProperty(DependencyProperty dp)
        {
            var descriptor = DependencyPropertyDescriptor.FromProperty(dp, typeof(AutoFitTextBlock));
            descriptor?.AddValueChanged(this, (_, _) =>
            {
                if (!_isAdjusting && dp == FontSizeProperty)
                    _baseFontSize = FontSize;

                AdjustFontSize();
            });
        }

        private static void OnAutoFitPropertyChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
        {
            if (d is AutoFitTextBlock tb)
                tb.AdjustFontSize();
        }

        private void AdjustFontSize()
        {
            if (_isAdjusting || !IsLoaded)
                return;

            if (ActualWidth <= 0 || string.IsNullOrWhiteSpace(Text))
                return;

            _isAdjusting = true;

            try
            {
                double startFont = _baseFontSize;
                double minFont = MinFontSize;

                FontSize = startFont;

                while (FontSize > minFont)
                {
                    if (Fits(FontSize))
                        return;

                    FontSize -= 0.5;
                }

                FontSize = minFont;
            }
            finally
            {
                _isAdjusting = false;
            }
        }

        private bool Fits(double fontSize)
        {
            double pixelsPerDip = VisualTreeHelper.GetDpi(this).PixelsPerDip;

            var formattedText = new FormattedText(
                Text ?? string.Empty,
                CultureInfo.CurrentUICulture,
                FlowDirection,
                new Typeface(FontFamily, FontStyle, FontWeight, FontStretch),
                fontSize,
                Foreground,
                pixelsPerDip)
            {
                MaxTextWidth = Math.Max(0, ActualWidth),
                Trimming = TextTrimming.None
            };

            if (TextWrapping == TextWrapping.Wrap)
                formattedText.MaxLineCount = MaxLines;

            double lineHeight = fontSize * 1.25;
            double maxAllowedHeight = lineHeight * MaxLines;

            return formattedText.Height <= maxAllowedHeight + 1;
        }
    }
}