>Hi,
>I am using [flag] enum to store combination of multiple value. How could I test if it contains certain value?
>
>Thank you

(you may know this, but just in case you don't) the [Flag] attribute isn't enough to make an enum addable (it changes the behavior of ToString()). You need to explicitly set the values, ex.

public enum Sample
{
   OptionOne = 1,
   OptionTwo = 2, 
   OptionThree = 4,
   OptionFour = 8
}

To determine which flags are set:

Sample sampleFlag = Sample.OptionTwo | Sample.OptionThree

if ((sampleFlag & Sample.OptionTwo) == Sample.OptionTwo)
   // Do something, OptionTwo is selected

if ((sampleFlag & Sample.OptionThree) == Sample.OptionThree)
   // Do something, OptionThree is selected