3rdpartylibs/fastreports.wpf/FastReport.Forms.WPF/CustomControls/CustomToolBarPanel.cs

using System;
using System.ComponentModel;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Forms;

namespace CustomControls
{
    [DesignTimeVisible(false)]
    public class CustomToolBarPanel : System.Windows.Controls.Primitives.ToolBarPanel
    {
        protected override Size MeasureOverride(Size constraint)
        {
            if (TemplatedParent is ToolBar tb && tb.Tag is StatusStrip)
            {
                double width = 0;
                foreach (FrameworkElement item in InternalChildren)
                {
                    item.Measure(constraint);
                    if (!(item.Tag is ToolStripStatusLabel lbl && lbl.Spring))
                        width += item.DesiredSize.Width;
                }

                double springWidth = Math.Max(constraint.Width - width, 0);
                foreach (FrameworkElement item in InternalChildren)
                {
                    if (item.Tag is ToolStripStatusLabel lbl && lbl.Spring)
                    {
                        item.Width = springWidth;
                        item.Height = constraint.Height;
                        item.Measure(new Size(item.Width, item.Height));
                    }
                }

                return constraint;
            }

            return base.MeasureOverride(constraint);
        }
    }
}