Use Microsoft Scripting Control to evaluate 'I

问题:

I have some c# code that uses the Microsoft Scripting Control to evaluate some expressions:

using MSScriptControl; // references msscript.ocx

ScriptControlClass sc = new ScriptControlClass();
sc.Language = "VBScript";
sc.AllowUI = true;

try
{
    Console.WriteLine(sc.Eval(txtEx.Text).ToString());
}
    catch (Exception ex)
{
    Console.WriteLine(ex.Message);
}

(txtEx is a simple text field)

Numerical expressions: "6+4", "cos(34)", "abs(-99)", "round(1.234, 2)" etc. are fine

Boolean expressions: "true or false", "1=2" are fine

But how can I evaluate a simple 'if'? I have tried "if(true, 2, 3)", "iif(true, 2, 3)", "if (true) then 2 else 3" and "if (true) then 2 else 3 endif"

Can anybody please help me to evaluate simple conditional expressions? Any help much appreciated!

RH

回答1:

Try wrapping your IF-expression in a function

Function test
   if (true) then
      return true
   else
      return false
   end if
End function

Add the function to the control and then use Run

Result = ScriptControl.Run("Test")

(the code above is not tested, but something along that way should work)

Check out this link for some more info

http://support.microsoft.com/kb/184740

回答2:

using MSScriptControl; // references msscript.ocx

ScriptControlClass sc = new ScriptControlClass();
sc.Language = "VBScript";
sc.AllowUI = true;

// VBScript engine doesn’t have IIf function
// Adding wraper IIF function to script control.
// This IIF function will work just as VB6 IIf function.
sc.AddCode(@"Function IIF(Expression,TruePart,FalsePart)
                If Expression Then
                    IIF=TruePart
                Else
                    IIF=FalsePart
                End IF
            End Function");
try
{
    //define x,y variable with value
    sc.AddCode(@"x=5
                y=6");
    //test our IIF 
    Console.WriteLine(sc.Eval("IIF(x>y,x,y)").ToString());
}
catch (Exception ex)
{
    Console.WriteLine(ex.Message);
}

回答3:

You should consider using the expression evaluation engine that is part of Windows Workflow Foundation. Both the evaluator and the designer for it can be used separately from WF.

回答4:

if (true) then return 2 else return 3

回答5:

Thanks for the tips! After a bit more experimenting, based on Brummo's help, this seems to work:

txtEx contains this text:

function test
  if (1=1) then 
    test = true
  else 
    test = false
  end if
end function

then

sc.AddCode(txtEx.Text);

and

object[] myParams = { };
Console.WriteLine(sc.Run("Test", ref myParams).ToString());

This isn't ideal, since I really wanted to evaluate an expression, without building, loading and evaluating a function. (I am surprised IIF doesn't work for simple one line if evaluation).