只读值的优雅解决方案

Question

我正在开发WPF应用程序，其窗口大小和组件位置必须在初始化时动态计算，因为它们基于我使用的主要UserControl大小和其他一些次要大小设置。因此，目前，我将这些常量值放置在Window代码中，如下所示：

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;

然后，只需在XAML中使用它们，如下所示：

<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}">

好吧...没什么好说的。它可以工作...但是很难看，我想知道是否有更好的解决方案。我不知道...可能是设置文件，绑定，内联XAML计算或其他任何内容...会使它看起来更好的东西。

Answer 1

我通常将所有静态应用程序设置都放在一个称为泛型的静态或单例类中，例如ApplicationSettings（或者MainWindowSettings如果这些值仅由所使用MainWindow）

如果这些值是用户可配置的，则将它们放入app.config中并加载到静态类的构造函数中。如果没有，我只是将它们硬编码在我的静态类中，这样以后就可以轻松找到/更改它们。

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;
    }
}

对于XAML中的计算值，通常使用我编写的MathConverter，它使我可以编写带有数学表达式的绑定，然后将要使用的值传递给它。

我在博客上发布的版本仅为IValueConverter，但将其扩展为相当容易，IMultiValueConverter因此可以接受多个绑定值。

<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>

通常，我会将所有这些杂乱的XAML隐藏在某个地方的样式中，这样就不会弄乱我的主要XAML代码，只需在需要的地方应用样式即可。

这是我用于的转换器代码的副本 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;
    }
}

但是老实说，如果这些值仅以一种形式使用，那么我只是Loaded在View后面的代码中的事件中设置这些值：）