如何使用标签文本中的公式进行计算 [英] How do I use formula from label text to calculate

问题描述

我正在创建用于计算物品重量的表格





我以字符串格式将公式存储到数据库中。



在计算的时候，我把这个公式带到我的表格中，我从用户那里获取价值。



公式是（val1-val2）* val2 * 0.00314 * val3



在用户输入后我更换了val1，val2&的值val3与用户输入



所以基本上我的公式就像（51-5）* 5 * 0.00314 * 4在这51,5,4是用户输入



我将此公式存储到标签



现在我想用这个公式来计算重量，所以我将标签值转换为双倍。



但它显示错误输入字符串的格式不正确。



任何人都可以帮助我。



我尝试过：

I was creating Form for calculating weight of item


I was stored formula to database in string format.

While calculating i was take that formula to label in my form and i am taking value from user.

the Formula is "(val1-val2)*val2*0.00314*val3"

after taking user input i was replace the value of val1, val2 & val3 with user input

so basically my formula is like "(51-5)*5*0.00314*4" in this 51,5,4 is user inputs

and i am store this formula to label

now i want to use that formula for calculating weight, so i am convert label value to double.

But it shows me error "input string is not in correct format."

Can anyone help me.

What I have tried:

Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
       Dim bindformula As String = lblActualFormula.Text
       bindformula = bindformula.Replace("Val1", txtOd.Text)
       bindformula = bindformula.Replace("Val2", txtWT.Text)
       bindformula = bindformula.Replace("Val3", txtLength.Text)
       lblBindFormula.Text = bindformula
   End Sub


   Private Sub Button2_Click(sender As Object, e As EventArgs) Handles Button2.Click
       Dim val As Double = Double.Parse(lblBindFormula.Text)
       MsgBox(val.ToString())
   End Sub

推荐答案

您不能只尝试将表达式解析为值 - 它不能像那样工作。

你需要正确评估它 - tehre是本网站上的几位评估员：微小的表达评估器 [ ^ ]是一个很好的，您可以添加其程序集作为项目的引用，并直接从VB调用它。

You can't just try to parse an expression to a value - it doesn't work like that.
You need to evaluate it properly instead - tehre are several evaluators on this site: A Tiny Expression Evaluator[^] is a good one, and you can add its assembly as a reference to your project and call it direct from VB.

您可以使用非常快速和灵活的 .NET的计算引擎 [ ^ ]。



其他资源：

重新访问表达式评估程序（100％托管.NET中的Eval函数） [ ^ ]

使用DynamicMethod .Net Expression Evaluator [ ^ ]



如果您想了解它的工作原理，请阅读：在VB.NET中解析数学表达式：可能的任务 [ ^ ]

You can use very fast and flexible A Calculation Engine for .NET[^].

Other resources:
The expression evaluator revisited (Eval function in 100% managed .NET)[^]
.Net Expression Evaluator using DynamicMethod[^]

If you would like to understand how it works, please read: Parsing Mathematical Expressions in VB.NET: Mission Possible[^]

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