只需要对swift 3中的功能提供一点指导

你看,你所有的按钮动作都是这样的:

    let billTotal = Double(subtotalText.text!)!
    let grandTotal = (billTotal * tipArray[x]) + billTotal

    //return grandTotal
    totalAmountLbl.text = String(format: "%.2f", grandTotal)

x 价值为了简化代码,您可以将整个内容提取到如下方法中:

func outputGrandTotal(tipIndex: Int) {
    let billTotal = Double(subtotalText.text!)!
    let grandTotal = (billTotal * tipArray[tipIndex]) + billTotal

    //return grandTotal
    totalAmountLbl.text = String(format: "%.2f", grandTotal)
}

@IBAction func fiveBtn(_ sender: Any) {
    outputGrandTotal(tipIndex: 0)

}

@IBAction func tenBtn(_ sender: Any) {
    outputGrandTotal(tipIndex: 1)

}

@IBAction func fifteenBtn(_ sender: Any) {
    outputGrandTotal(tipIndex: 2)

}

@IBAction func twentyBtn(_ sender: Any) {

    outputGrandTotal(tipIndex: 3)

}

@IBAction func twentyfiveBtn(_ sender: Any) {
    outputGrandTotal(tipIndex: 4)
}

@IBAction func thirtyBtn(_ sender: Any) {
    outputGrandTotal(tipIndex: 5)

}

tag 你所有的按钮。那你只需要一个 @IBAction

@IBAction func tipButtonTapped(_ sender: UIButton) {
    outputGrandTotal(tipIndex: sender.tag)
}