I want to create this type of fixture in one body. Here square and circle both are different fixtures but attach to one body. How do I do this?
I'm not sure how this is done specifically in Objective-C, but in normal C++ Box2D you just need to call the method createFixture("Fixture") on the body two times, one with the characteristics of the square, and another with the circle. See the manual in http://www.box2d.org/manual.html#_Toc258082972.