Question

OK, so I am pretty sure I’m on the right track with this small application, but let me know. The user enters in 3 of the 4 numbers into the 4 editable textboxes, and the missing number is calculated automatically. Picture of app here:

http://www.peauproductions.com/images/lens_app.PNG

I have looked at data binding, and I think I need to have the values able to globally change. I want the values to dynamically update/compute and not have to have a calculate button.

Once I get it working I need to implement a validation check to make sure a boolean is only entered (no text), and have a tooltip pop up saying to enter a number.

Getting the following ERROR right now:

“‘Set property ‘System.Windows.Controls.TextBox.Text’ threw an exception.’ Line number ’56’ and line position ’51’.”

MainWindow.xaml Code:

<Window x:Class="ConverterApp.MainWindow"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    Title="ConverterApp" Height="360" Width="280"
    xmlns:c="clr-namespace:ConvertorApp;assembly=">

<Grid>
    <!--Outer Box + Title-->
    <TextBox Height="309" Width="248"
    Text=" Lens Calculator"
    IsReadOnly="True" 
    Margin="5,5,0,0"
    VerticalAlignment="Top"
    HorizontalAlignment="Left"
    BorderThickness="2.0"
    FontSize="16" FontFamily="Verdana" FontWeight="Bold">
        <TextBox.BorderBrush>
            <LinearGradientBrush StartPoint="0,0" EndPoint="1,1" >
                <GradientStop Color="Black" Offset="0" />
            </LinearGradientBrush>
        </TextBox.BorderBrush> 
    </TextBox>

    <!--Title Text-->
    <TextBox Height="50" Width="230"
    Text="Enter Image Width, Length and Either Distance or Lens Values Below"
    IsReadOnly="True" 
    Margin="14,29,0,0"
    TextWrapping="Wrap"
    VerticalAlignment="Top"
    HorizontalAlignment="Left"
    FontSize="12" FontFamily="Verdana"  FontStyle="Italic"
    BorderThickness="0">        
    </TextBox>

    <TextBox Height="20" Width="230"
    Text="Must Be Same Units (in,ft,cm,mm)"
    IsReadOnly="True" 
    Margin="14,59,0,0"
    VerticalAlignment="Top"
    HorizontalAlignment="Left"
    FontSize="10" FontFamily="Verdana" FontStyle="Italic"
    BorderThickness="0">
    </TextBox>

    <!--Distance-->
    <TextBox Height="20" Width="105"
    Text="Distance/Height:"
    IsReadOnly="True" 
    Margin="15,80,0,0"
    VerticalAlignment="Top"
    HorizontalAlignment="Left"
    FontFamily="Verdana"
    BorderThickness="0">
    </TextBox>

    <TextBox x:Name="DistanceBox" Height="20" Width="50"
    Text="{x:Static c:Variables.DistanceBox}"
    Margin="125,80,0,0"
    MaxLength="5" 
    VerticalAlignment="Top"
    HorizontalAlignment="Left"
    FontFamily="Verdana">
        <TextBox.BorderBrush>
            <LinearGradientBrush StartPoint="0,0" EndPoint="1,1" >
                <GradientStop Color="Black" Offset="0" />
            </LinearGradientBrush>
        </TextBox.BorderBrush>
    </TextBox>

    <!--Image Width-->
    <TextBox Height="20" Width="90"
    Text="Image Width:"
    IsReadOnly="True" 
    Margin="15,105,0,0"
    VerticalAlignment="Top"
    HorizontalAlignment="Left"
    FontFamily="Verdana"
    BorderThickness="0">
    </TextBox>

    <TextBox x:Name="WidthBox" Height="20" Width="50"
    Text="{x:Static c:Variables.WidthBox}"
    Margin="125,105,0,0"
    MaxLength="5" 
    VerticalAlignment="Top"
    HorizontalAlignment="Left"
             FontFamily="Verdana">
        <TextBox.BorderBrush>
            <LinearGradientBrush StartPoint="0,0" EndPoint="1,1" >
                <GradientStop Color="Black" Offset="0" />
            </LinearGradientBrush>
        </TextBox.BorderBrush>
    </TextBox>

    <!--Image Length-->
    <TextBox Width="95"
    Text="Image Length:"
    IsReadOnly="True" 
    Margin="15,130,0,161" HorizontalAlignment="Left"
    FontFamily="Verdana"
    BorderThickness="0">
    </TextBox>

    <TextBox x:Name="LengthBox" Height="20" Width="50"
    Text="{x:Static c:Variables.LengthBox}"
    Margin="125,130,0,0"
             MaxLength="5" 
    VerticalAlignment="Top"
    HorizontalAlignment="Left"
             FontFamily="Verdana">
        <TextBox.BorderBrush>
            <LinearGradientBrush StartPoint="0,0" EndPoint="1,1" >
                <GradientStop Color="Black" Offset="0" />
            </LinearGradientBrush>
        </TextBox.BorderBrush>
    </TextBox>

    <!--Lens Needed-->
    <TextBox Height="20" Width="90"
    Text="Lens (mm):"
    IsReadOnly="True" 
    Margin="15,155,0,0"
    VerticalAlignment="Top"
    HorizontalAlignment="Left"
    FontFamily="Verdana"
    BorderThickness="0">
    </TextBox>

    <TextBox x:Name="LensNeeded" Height="20" Width="50"
    Text="{x:Static c:Variables.LensNeeded}"
    Margin="125,155,0,0"
             MaxLength="4" 
    VerticalAlignment="Top"
    HorizontalAlignment="Left"
             FontFamily="Verdana">
        <TextBox.BorderBrush>
            <LinearGradientBrush StartPoint="0,0" EndPoint="1,1" >
                <GradientStop Color="Black" Offset="0" />
            </LinearGradientBrush>
        </TextBox.BorderBrush>
    </TextBox>

    <!--Info-->
    <TextBox Height="70" Width="230"
    Text="The lens focal length value represents the estimated mm value for a 1/4 inch sensor (Playstation Eye).  A lower mm will give a wider Field of View (FOV), and a higher value less FOV. "
    IsReadOnly="True" 
    TextWrapping="Wrap"
    Margin="15,180,0,0"
    FontSize="11"
    VerticalAlignment="Top"
    HorizontalAlignment="Left"
    FontFamily="Verdana"  FontStyle="Italic"
    BorderThickness="0">
    </TextBox>
    <TextBox Height="55" Width="230"
    Text="It is not recommend you use a lens of less than 2.5mm focal length with image tracking software due to distortion."
    IsReadOnly="True"
    FontSize="11"
    TextWrapping="Wrap"
    Margin="15,253,0,0"
    VerticalAlignment="Top"
    HorizontalAlignment="Left"
    FontFamily="Verdana"  FontStyle="Italic"
    BorderThickness="0">
    </TextBox>


</Grid>

MainWindow.xaml.cs Code:

using System;
using System.Windows;

namespace ConvertorApp
{
    public class Variables
    {
        public const double DistanceBox = 0;
        public const double WidthBox = 0;
        public const double LengthBox = 0;
        public const double LensNeeded = 0;
        public const double WidthBased = 0;
        public const double LengthBased = 0;

        public void Calc()
        {
            double WidthBased = 2.952*(DistanceBox/WidthBox);
            double LengthBased = 3.984*(DistanceBox/LengthBox);

            if (WidthBased < LengthBased)
            {
                double LensNeeded = WidthBased;
            }else{
                double LensNeeded = LengthBased;
            }
        }
    }
}

If you can think of an easier, or more correct way to go about what I’m trying to do, please let me know (I just started learning this WPF/C# stuff). Thanks

---

UPDATE:

Here is the back code showing suggested changes from below:

    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
            {
                m_distanceBox = value;
                // modify calc to read the text values
                Calc();
                // Call NotifyPropertyChanged when the source property 
                // is updated.
                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));
            }
        }
    }
}

**ERROR I’m now getting is the StackOverflowException on the get {} inside the double functions. Any ideas?

Answer 1

The exception is thrown because the line

Text="{x:Static c:Variables.DistanceBox}"

is effectively something like

textBox.Text = Variables.DistanceBox;

This wouldn’t compile in C#. In XAML, it throws exception. What you should do instead is create properties from your fields:

public double DistanceBox { get; set; }

And set Variables as DataContext of your window, by adding

DataContext = new Variables();

to the constructor of your window (or handler of the Loaded event).

You then use bindings in your XAML (which uses a converter to make strings out of doubles):

Text="{Binding DistanceBox}"

To call Calc() whenever a value changes, you can change the property to

private double m_distanceBox;
public double DistanceBox
{
    get { return m_distanceBox; }
    set
    {
        m_distanceBox = value;
        Calc();
    }
}

To make sure changes in Variables are reflected in the text boxes, you should implement the INotifyPropertyChanged interface.

EDIT: C# code of MainWindow:

public partial class MainWindow
{
    public MainWindw()
    {
        InitializeComponent();
        DataContext = new Variables();
    }
}