动态代码执行：字符串->运行时代码VB.net [英] Dynamic code execution: String -> Runtime code VB.net

问题描述

我正在尝试在运行时在字符串内执行一些代码。 IE

I'm trying to execute some code inside a string in runtime. I.E.

Dim code As String = "IIf(1 = 2, True, False)"

我如何在 code 字符串中运行代码？

How do i run the code inside code string ?

推荐答案

正如@ElektroStudios所说-正确的方法是使用 CodeDom编译器，但这对于像这样简单的东西来说有点过分了。

As @ElektroStudios said - the proper way to do this is to use the CodeDom compiler, but this is a bit overkill for something as simple as this.

欺骗并利用 DataColumn表达式

的力量，例如：

    Dim formula = "IIF(Condition = 'Yes', 'Go', 'Stop')"
    Dim value As String = "Yes"
    Dim result As String

    'add a columns to hold the value
    Dim colStatus As New DataColumn
    With colStatus
        .DataType = System.Type.GetType("System.String")
        .ColumnName = "Condition"
    End With

    'add a column to compute the expression
    Dim colExp As New DataColumn
    With colExp
        .DataType = System.Type.GetType("System.String")
        .ColumnName = "Expression"
        .Expression = formula
    End With

    'create a table and add the columns
    Dim dt As New DataTable
    With dt.Columns
        .Add(colStatus)
        .Add(colExp)
    End With

    'now add a row and set the condition to the value we have
    Dim row As DataRow = dt.NewRow
    row.SetField(Of String)("Condition", value)
    dt.Rows.Add(row)

    'now read back the computed value based on the expression being evaluated
    result = row.Field(Of String)("Expression")
    MessageBox.Show(result)

您可以将所有这些包装成一个更通用的函数，如下所示：

You could wrap all this up into a more generic function like this:

Public Function EvaluateExpression(Of T, K)(input As T, formula As String) As K
    'add a columns to hold the value
    Dim colStatus As New DataColumn
    With colStatus
        .DataType = GetType(T)
        .ColumnName = "Condition"
    End With

    'add a column to compute the expression
    Dim colExp As New DataColumn
    With colExp
        .DataType = GetType(K)
        .ColumnName = "Expression"
        .Expression = formula
    End With

    'create a table and add the columns
    Dim dt As New DataTable
    With dt.Columns
        .Add(colStatus)
        .Add(colExp)
    End With

    'now add a row and set the condition to the value we have
    Dim row As DataRow = dt.NewRow
    row.SetField(Of T)("Condition", input)
    dt.Rows.Add(row)

    'now read back the computed value based on the expression being evaluated
    Return row.Field(Of K)("Expression")
End Function

所以你可以给我打电话像这样：

So then you can call it like this:

Dim result = EvaluateExpression(Of Integer, Boolean)(1, "IIF(Condition = 1, True, False)")

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