Elegant Solution for Readonly Values

Question

I'm developing a WPF application whose Window size and component locations must be dynamically calculated upon initialization because they are based on the main UserControl size I use and some other minor size settings. So, for the moment, I've placed those constant values in my Window code as follows:

public const Double MarginInner = 6D;
public const Double MarginOuter = 10D;
public const Double StrokeThickness = 3D;

public static readonly Double TableHeight = (StrokeThickness * 2D) + (MarginInner * 3D) + (MyUC.RealHeight * 2.5D);
public static readonly Double TableLeft = (MarginOuter * 3D) + MyUC.RealHeight + MarginInner;
public static readonly Double TableTop = MarginOuter + MyUC.RealHeight + MarginInner;
public static readonly Double TableWidth = (StrokeThickness * 2D) + (MyUC.RealWidth * 6D) + (MarginInner * 7D);
public static readonly Double LayoutHeight = (TableTop * 2D) + TableHeight;
public static readonly Double LayoutWidth = TableLeft + TableWidth + MarginOuter;

Then, I just use them inside my XAML as follows:

<Window x:Class="MyNS.MainWindow" ResizeMode="NoResize" SizeToContent="WidthAndHeight">
    <Canvas x:Name="m_Layout" Height="{x:Static ns:MainWindow.LayoutHeight}" Width="{x:Static ns:MainWindow.LayoutWidth}">

Well... nothing to say. It works... but it's soooo damn ugly to see and I was wondering if there is any better solution for this. I don't know... maybe a Settings file, bindings, inline XAML calculations or whatever else... something that would make it just look better.

Answer 1

I usually put all static my application settings in a single static or singleton class called something generic, like ApplicationSettings (or MainWindowSettings if the values are only used by the MainWindow)

If the values are meant to be user-configurable, they go in app.config and get loaded in the constructor of the static class. If not, I just hard code them in my static class so they're easy to find/change later on.

public static class ApplicationSettings
{
    public static Double MarginInner { get; private set; }
    public static Double MarginOuter { get; private set; }
    public static Double StrokeThickness { get; private set; }

    static ApplicationSettings()
    {
        MarginInner = 6D;
        MarginOuter = 10D;
        StrokeThickness = 3D;
    }
}

For calculated values in your XAML, I typically use a MathConverter I wrote that lets me write a binding with a mathematical expression, and pass it the values to use.

The version I have posted on my blog is only an IValueConverter, but it's pretty easy to expand into an IMultiValueConverter so it can accept multiple bound values.

<Setter Property="Height">
   <Setter.Value>
      <MultiBinding Converter="{StaticResource MathMultiConverter}"
                    ConverterParameter="(@VALUE1 * 2D) + (@VALUE2 * 3D) + (@VALUE3 * 2.5D)">
         <Binding RelativeSource="{x:Static ns:ApplicationSettings.StrokeThickness }" />
         <Binding RelativeSource="{x:Static ns:ApplicationSettings.MarginInner}" />
         <Binding ElementName="MyUc" Path="ActualHeight" />
      </MultiBinding>
   </Setter.Value>
</Setter>

Normally I would hide all this messy XAML in a Style somewhere, so it doesn't clutter up my main XAML code, and just apply the style where needed.

Here's a copy of the converter code I use for the IMultiValueConvter

// Does a math equation on a series of bound values. 
// Use @VALUEN in your mathEquation as a substitute for bound values, where N is the 0-based index of the bound value
// Operator order is parenthesis first, then Left-To-Right (no operator precedence)
public class MathMultiConverter : IMultiValueConverter
{
    public object  Convert(object[] values, Type targetType, object parameter, CultureInfo culture)
    {
        // Remove spaces
        var mathEquation = parameter as string;
        mathEquation = mathEquation.Replace(" ", "");

        // Loop through values to substitute placeholders for values
        // Using a backwards loop to avoid replacing something like @VALUE10 with @VALUE1
        for (var i = (values.Length - 1); i >= 0; i--)
            mathEquation = mathEquation.Replace(string.Format("@VALUE{0}", i), values[i].ToString());

        // Return result of equation
        return MathConverterHelpers.RunEquation(ref mathEquation);
    }

    public object[]  ConvertBack(object value, Type[] targetTypes, object parameter, CultureInfo culture)
    {
        throw new NotImplementedException();
    }
}

public static class MathConverterHelpers
{
    private static readonly char[] _allOperators = new[] { '+', '-', '*', '/', '%', '(', ')' };

    private static readonly List<string> _grouping = new List<string> { "(", ")" };
    private static readonly List<string> _operators = new List<string> { "+", "-", "*", "/", "%" };


    public static double RunEquation(ref string mathEquation)
    {
        // Validate values and get list of numbers in equation
        var numbers = new List<double>();
        double tmp;

        foreach (string s in mathEquation.Split(_allOperators))
        {
            if (s != string.Empty)
            {
                if (double.TryParse(s, out tmp))
                {
                    numbers.Add(tmp);
                }
                else
                {
                    // Handle Error - Some non-numeric, operator, or grouping character found in string
                    throw new InvalidCastException();
                }
            }
        }

        // Begin parsing method
        EvaluateMathString(ref mathEquation, ref numbers, 0);

        // After parsing the numbers list should only have one value - the total
        return numbers[0];
    }

    // Evaluates a mathematical string and keeps track of the results in a List<double> of numbers
    private static void EvaluateMathString(ref string mathEquation, ref List<double> numbers, int index)
    {
        // Loop through each mathemtaical token in the equation
        string token = GetNextToken(mathEquation);

        while (token != string.Empty)
        {
            // Remove token from mathEquation
            mathEquation = mathEquation.Remove(0, token.Length);

            // If token is a grouping character, it affects program flow
            if (_grouping.Contains(token))
            {
                switch (token)
                {
                    case "(":
                        EvaluateMathString(ref mathEquation, ref numbers, index);
                        break;

                    case ")":
                        return;
                }
            }

            // If token is an operator, do requested operation
            if (_operators.Contains(token))
            {
                // If next token after operator is a parenthesis, call method recursively
                string nextToken = GetNextToken(mathEquation);
                if (nextToken == "(")
                {
                    EvaluateMathString(ref mathEquation, ref numbers, index + 1);
                }

                // Verify that enough numbers exist in the List<double> to complete the operation
                // and that the next token is either the number expected, or it was a ( meaning 
                // that this was called recursively and that the number changed
                if (numbers.Count > (index + 1) &&
                    (double.Parse(nextToken) == numbers[index + 1] || nextToken == "("))
                {
                    switch (token)
                    {
                        case "+":
                            numbers[index] = numbers[index] + numbers[index + 1];
                            break;
                        case "-":
                            numbers[index] = numbers[index] - numbers[index + 1];
                            break;
                        case "*":
                            numbers[index] = numbers[index] * numbers[index + 1];
                            break;
                        case "/":
                            numbers[index] = numbers[index] / numbers[index + 1];
                            break;
                        case "%":
                            numbers[index] = numbers[index] % numbers[index + 1];
                            break;
                    }
                    numbers.RemoveAt(index + 1);
                }
                else
                {
                    // Handle Error - Next token is not the expected number
                    throw new FormatException("Next token is not the expected number");
                }
            }

            token = GetNextToken(mathEquation);
        }
    }

    // Gets the next mathematical token in the equation
    private static string GetNextToken(string mathEquation)
    {
        // If we're at the end of the equation, return string.empty
        if (mathEquation == string.Empty)
        {
            return string.Empty;
        }

        // Get next operator or numeric value in equation and return it
        string tmp = "";
        foreach (char c in mathEquation)
        {
            if (_allOperators.Contains(c))
            {
                return (tmp == "" ? c.ToString() : tmp);
            }
            else
            {
                tmp += c;
            }
        }

        return tmp;
    }
}

But quite honestly, if these values are only used in a single form then I'd just set the values in the Loaded event in the code behind the View :)

Answer 2

Put those static ones in the app.config, they'd be much cleaner in there.

Using app.config, you'd first have to have a reference to System.Configuration.

Then you can do (there may be some type casting involved):

 ConfigurationManager.AppSettings["MarginInner"];

To retrieve:

<configuration>
    <appsettings>
        <add key="MarginInner" value="6D" />
    </appsettings>
</configuration>

Then maybe have a static class to hold the dynamic calculations, something like:

public class CalculationHelper
{
    //your dynamic properties in here
}

Answer 3

mattytommo`s answer only addresses the constant values you have (margins and stroke thickness) but not the calculated fields.

I would, in conjuction with what Matty said, add a settings class that retrieves the constant values from the app.config file and also does the appropriate calculations needed and then I could reference the appropriate property in the XAML

i.e.

{ Settings.MainWindow.LayoutWidth }

EDIT :

it looks like Matty had the same though as he edited in between me posting ;)