resignFirstResponder没有隐藏iPad中的UIkeyboard

I have an iPad application in which resignFirstResponder does't seems to be working. I have tried many solutions. I am just calling resign first responder from the instance of the firstResponder object but keyboard is remain there on the screen. THen I tried by iterating all the window to get the instance of the first responder and then I am calling the resignFirstResponder from that instance.I have an iPad application in which resignFirst