c# - 创建动态公式

Question

我需要创建一个用户界面，用户将建立一个公式。即:

对于一个项目公式是:

成本 * 项目/100

对于另一个项目:

项目* 5/100

我希望用户能够通过网络用户界面生成公式。

然后当用户输入我想要计算结果的变量时。

是否有任何软件包或插件可以做到这一点？

谢谢。

Answer 1

达斯维德!

这里有几个选项，这取决于您的需求以及您是需要非常复杂的东西还是简单易懂和扩展的东西(可能出于学术目的)。

1) 让我们从简单、容易和可定制开始。我已经创建了一个满足您在帖子中指定的需求的类，但是它非常原始，不应该在没有进一步测试和修改的情况下用于商业项目......如果您可以轻松地选择它并增加它想要...它显示了一种实现所需内容的简单方法。该代码运行良好，但未考虑数学优先级(例如括号或 * 优于 +)。它需要进行调整才能这样做...... 代码在下面，它被注释并希望能够 self 解释:

public class DynamicFormula
{
    /// <summary>
    /// This simply stores a variable name and its value so when this key is found in a expression it gets the value accordingly.
    /// </summary>
    public Dictionary<string, double> Variables { get; private set; }

    /// <summary>
    /// The expression itself, each value and operation must be separated with SPACES. The expression does not support PARENTHESES at this point.
    /// </summary>
    public string Expression { get; set; }

    public DynamicFormula()
    {
        this.Variables = new Dictionary<string, double>();
    }

    public double CalculateResult()
    {
        if (string.IsNullOrWhiteSpace(this.Expression))
            throw new Exception("An expression must be defined in the Expression property.");

        double? result = null;
        string operation = string.Empty;

        //This will be necessary for priorities operations such as parentheses, etc... It is not being used at this point.
        List<double> aux = new List<double>();  

        foreach (var lexema in Expression.Split(new string[] { " " }, StringSplitOptions.RemoveEmptyEntries))
        {
            //If it is an operator
            if (lexema == "*" || lexema == "/" || lexema == "+" || lexema == "-")
            {
                operation = lexema;
            }
            else //It is a number or a variable
            {
                double value = double.MinValue;
                if (Variables.ContainsKey(lexema.ToLower())) //If it is a variable, let's get the variable value
                    value = Variables[lexema.ToLower()];
                else //It is just a number, let's just parse
                    value = double.Parse(lexema);

                if (!result.HasValue) //No value has been assigned yet
                {
                    result = value;
                }
                else
                {
                    switch (operation) //Let's check the operation we should perform
                    {
                        case "*":
                            result = result.Value * value;
                            break;
                        case "/":
                            result = result.Value / value;
                            break;
                        case "+":
                            result = result.Value + value;
                            break;
                        case "-":
                            result = result.Value - value;
                            break;
                        default:
                            throw new Exception("The expression is not properly formatted.");
                    }
                }
            }
        }

        if (result.HasValue)
            return result.Value;
        else
            throw new Exception("The operation could not be completed, a result was not obtained.");
    }
    /// <summary>
    /// Add variables to the dynamic math formula. The variable should be properly declared.
    /// </summary>
    /// <param name="variableDeclaration">Should be declared as "VariableName=VALUE" without spaces</param>
    public void AddVariable(string variableDeclaration)
    {            
        if (!string.IsNullOrWhiteSpace(variableDeclaration))
        {
            var variable = variableDeclaration.ToLower().Split('=');    //Let's make sure the variable's name is LOWER case and then get its name/value
            string variableName = variable[0];
            double variableValue = 0;

            if (double.TryParse(variable[1], out variableValue))
                this.Variables.Add(variableName, variableValue);
            else
                throw new ArgumentException("Variable value is not a number");
        }
        else
        {
            //Could throw an exception... or just ignore as it not important...
        }
    }
}

这是一个在 WPF 应用程序中使用上述类的示例(可以在任何 C# 应用程序中使用)

    private void btCalculate_Click(object sender, RoutedEventArgs e)
    {
        string expression = tboxExpression.Text;    //"cost * item / 100" (IT MUST BE SEPARATED WITH SPACES!)
        string variable1 = tboxVariable1.Text;      //"item=10"
        string variable2 = tboxVariable2.Text;      //"cost=2.5"

        DynamicFormula math = new DynamicFormula();
        math.Expression = expression;   //Let's define the expression
        math.AddVariable(variable1);    //Let's add the first variable
        math.AddVariable(variable2);    //Let's add the second variable

        try
        {
            double result = math.CalculateResult(); //In this scenario the result is 0,25... cost * item / 100 = (2.5 * 10 / 100) = 0,25
            //Console.WriteLine("Success: " + result);
            tboxResult.Text = result.ToString();
        }
        catch(Exception ex)
        {
            //Console.WriteLine(ex.Message);
            tboxResult.Text = ex.Message;
        }
    }

2) 如果您需要更强大的东西并且适用于大多数现实生活情况，您应该明确检查 FLEE: http://flee.codeplex.com/wikipage?title=Examples&referringTitle=Home

这是一个专门为此制作的库，它支持多种公式! 可能需要一些时间才能看到一些示例并理解它是如何工作的，但它应该可以在不做太多工作的情况下完成工作。

希望对你有帮助，

路易斯·恩里克·戈尔。