vb.net - 动态代码执行 : String -> Runtime code VB.net

Question

我正在尝试在运行时在字符串中执行一些代码。 IE。

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

我如何运行里面的代码 code字符串 ？

Answer 1

正如@ElektroStudios 所说 - 正确的方法是使用 CodeDom compiler ，但这对于像这样简单的事情来说有点矫枉过正。

你可以欺骗和利用 DataColumn Expression 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:

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

那么你可以这样称呼它:

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