WPF4/C# - System.StackOverflowException Crashing App

Question

Below you can see my .xaml.cs code. The app opens fine. There are 4 textboxes which the user can change. When you edit one of the default values in the textboxes and then click off to not select it, the app crashes with the System.StackOverflowException error, saying I have an infinite loop or recursion on either the get{} or Calc() function, depending on which textbox is edited. I want the app to calculate the numbers according to the Calc() function every time a textbox is not being edited. I also would like to define some starting values for the textboxes, but haven't figured out how to do that yet.

Any ideas how I can fix the loop error and initial value defines?

The textboxes in the .xaml code follow this pattern: Text="{Binding DistanceBox}"

The full behind code is as follows:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Navigation;
using System.Windows.Shapes;
using System.ComponentModel;

namespace ConverterApp
{
    public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();
            DataContext = new Variables();
        }
    }

    public class Variables : INotifyPropertyChanged
    {
        // Declare the PropertyChanged event.
        public event PropertyChangedEventHandler PropertyChanged;

        private double m_distanceBox;
        public double DistanceBox
        {
            get { return m_distanceBox; }
            set
            {
                //If value hasn't changed, don't do anything
                //if (m_distanceBox == value)
                //    return;
                m_distanceBox = value;
                // modify calc to read the text values
                Calc();
                // Call NotifyPropertyChanged when the source property
                // is updated.
                //if(PropertyChanged!= null)
                    NotifyPropertyChanged("DistanceBox");
            }
        }

        private double m_widthBox;
        public double WidthBox
        {
            get { return m_widthBox; }
            set
            {
                m_widthBox = value;
                // modify calc to read the text values
                Calc();
                // Call NotifyPropertyChanged when the source property
                // is updated.
                NotifyPropertyChanged("WidthBox");
            } 
        }

        private double m_lengthBox;
        public double LengthBox
        {
            get { return m_lengthBox; }
            set
            {
                m_lengthBox = value;
                // modify calc to read the text values
                Calc();
                // Call NotifyPropertyChanged when the source property
                // is updated.
                NotifyPropertyChanged("LengthBox");
            }
        }

        private double m_lensBox;
        public double LensNeeded
        {
            get { return m_lensBox; }
            set
            {
                m_lensBox = value;
                // modify calc to read the text values
                Calc();
                // Call NotifyPropertyChanged when the source property
                // is updated.
                NotifyPropertyChanged("LensNeeded");
            }
        }

        public void Calc()
        {
            double WidthBased = 2.95 * (DistanceBox / WidthBox);
            double LengthBased = 3.98 * (DistanceBox / LengthBox);

            if (WidthBased < LengthBased)
            {
                LensNeeded = Math.Round(WidthBased,2);
            }else{
                LensNeeded = Math.Round(LengthBased,2);
            }
        }

        // NotifyPropertyChanged will raise the PropertyChanged event,
        // passing the source property that is being updated.
        public void NotifyPropertyChanged(string propertyName)
        {
            if (PropertyChanged != null)
            {
                PropertyChanged(this,
                    new PropertyChangedEventArgs(propertyName));
            }
        }
    }
}

Answer 1

In your setter of LensNeeded you call Calc, calc in turn sets LensNeeded, the setter of LensNeeded calls Calc, etc. this circularity leads to the StackOverflow.

Do not calculate properties in setters like that, make the respective properties "virtual" (calculate the value on the fly rather than getting the value from a backing field), e.g.

public double WidthBased
{
    get { return 2.95 * (DistanceBox / WidthBox); }
}

To make the bindings to such properties update you can raise property changed events in all related properties' setters, here that would be the setters of DistanceBox and WidthBox.

private double m_distanceBox;
public double DistanceBox
{
    get { return m_distanceBox; }
    set
    {
        if (m_distanceBox != value)
        {
            m_distanceBox = value;
            NotifyPropertyChanged("DistanceBox");
            NotifyPropertyChanged("WidthBased");
        }
    }
}

---

Initial values could be set in the contructor of your variables class or directly in the field declarations, e.g.

private double m_distanceBox = 10;
public double DistanceBox //...