After reading the question (and I am also pointing out that I am not familiar with iOS in any way), you might want to edit it somewhat - as in the current reading - while there isn't anything that just out like a sore thumb, it also reads a bit like I want to do this magically without really having to do anything... anyone?
Now, given that you went to the trouble of using a nice image in your question to illustrate it, I am sure that it wasn't the way you meant to ask it - but if you include things like but I can't get the effect I want then you really should go out of your way to explain in detail what you have tried, and how the outcome differed from the result that you wanted.
People can and do downvote questions because they are vague, but people also downvote questions that appear to be vague. Remember, in asking a great question, put all the information into the question that will be required to answer it. And it really never, ever hurts to post some code in a question like this - perhaps a function param was a digit off, perhaps you should be using a different function - who knows or can pinpoint a problem without seeing it?
I might be a little harsh in this answer, but I am simply pointing out the reasons that people might be thinking and then downvoting. Looking at it, I would have asked for clarification on some points and probably not downvoted, but I also hardly ever downvote.