selector - Programming a UIButton is not working in Swift 4 Xcode 9 Beta 6, Cannot add target -

in past had no problem creating uibutton programmatically, ever since i've been using xcode 9 , swift 4, cannot find way make error go away.

//adding target uibutton func positionstartbutton(xoffset: float){     startbutton.frame = cgrect(x: int(0 - 40 + xoffset), y: 0, width: 80, height: 80)     startbutton.setimage(#imageliteral(resourcename: "logo_final_white_face"), for: .normal)     startbutton.addtarget(self, action: "pressbutton:", for: .touchupinside)     scrollview.addsubview(startbutton)  }  //the target function func pressbutton(_ sender: uibutton){     print("\(sender)") } 

error message: 'nsinvalidargumentexception', reason: '-[playing.mainmenuviewcontroller pressbutton:]: unrecognized selector sent instance 0x10440a6b0'

two points.

first, since swift 2.2 (bundled xcode 7.3, released more year ago), recommended selector notation #selector(...). using notation, may more useful diagnostic messages, using other notation.

(you should not ignore warnings displayed recommended settings.)

seconde, in swift 4, need explicitly annotate methods invoked through selector @objc. (in limited cases, swift implicitly applies notation, not many.)

so, code shown should be:

//adding target uibutton func positionstartbutton(xoffset: float){     startbutton.frame = cgrect(x: int(0 - 40 + xoffset), y: 0, width: 80, height: 80)     startbutton.setimage(#imageliteral(resourcename: "logo_final_white_face"), for: .normal)     startbutton.addtarget(self, action: #selector(self.pressbutton(_:)), for: .touchupinside) //<- use `#selector(...)`     scrollview.addsubview(startbutton)  }  //the target function @objc func pressbutton(_ sender: uibutton){ //<- needs `@objc`     print("\(sender)") } 

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this not critical, should better follow simple coding rule of swift -- type names capitalized.

better rename positionstartbutton, startbutton , scrollview, if think may have chance show code publicly.