Here[
^] is an article which describes different techniques for passing data between forms. :)
wrote:
I want to send some data from child form to already opened parent form
You can find simple solution to this problem by using the "Object Approach" described in the article. The sample code there is for passing data from parent to the child, but it is very easy to pass data from child to parent, using the described approach. Give it a try! :)