以快捷方式以编程方式定位微视图

Question

在你最后的帮助下，我的循环运转良好。但只有一次。如果我试图重新加载它，我会得到以下错误：“超出范围的索引”在下面的行中：

let cardOnTop = cards[index-8]

有人能帮我吗？

这是我的代码：

func layoutCards() {

        //  create cards array with several elements
        var cards = (1...64).map { _ in UIView() }// array with several cards


        //Loop through each card in the array
        for index in 0...cards.count-1 {



            // place the card in the view and turn off translateAutoresizingMask
            let thisCard = cards[index]

            thisCard.layer.borderWidth = 1
            thisCard.layer.borderColor = UIColor.blackColor().CGColor
            thisCard.backgroundColor = UIColor.greenColor()

            thisCard.translatesAutoresizingMaskIntoConstraints = false
            midView.addSubview(thisCard)

            //set the height and width constraints
            let widthConstraint = NSLayoutConstraint(item: thisCard, attribute: .Width, relatedBy: .Equal, toItem: midView, attribute: .Width, multiplier: 0.125, constant: 0)
            let heightConstraint = NSLayoutConstraint(item: thisCard, attribute: .Height, relatedBy: .Equal, toItem: midView, attribute: .Height, multiplier: 0.125, constant: 0)
            midView.addConstraints([heightConstraint, widthConstraint])

            //set the horizontal  position

            if (columnCounter > 0) {

                // card is not in the first column
                let cardOnTheLeft = cards[index-1]

                let leftSideConstraint = NSLayoutConstraint(item: thisCard, attribute: .Left, relatedBy: .Equal, toItem: cardOnTheLeft, attribute: .Right, multiplier: 1, constant: 0)

                //add constraint to the contentView
                midView.addConstraint(leftSideConstraint)

            } else {

                //card is in the first column

                let leftSideConstraint = NSLayoutConstraint(item: thisCard, attribute: .Left, relatedBy: .Equal, toItem: midView, attribute: .Left, multiplier: 1, constant: 0)

                //add constraint to the contentView
                midView.addConstraint(leftSideConstraint)

            }


            //set the vertical position

            if (rowCounter > 0) {

                // card is not in the first row
                let cardOnTop = cards[index-8]

                let topConstraint = NSLayoutConstraint(item: thisCard, attribute: .Top, relatedBy: .Equal, toItem: cardOnTop, attribute: .Bottom, multiplier: 1, constant: 0)

                // add constraint to the contentView
                midView.addConstraint(topConstraint)

            } else {

                //card is in the first row

                let topConstraint = NSLayoutConstraint(item: thisCard, attribute: .Top, relatedBy: .Equal, toItem: midView, attribute: .Top, multiplier: 1, constant: 0)

                //add constraint to the contentView
                midView.addConstraint(topConstraint)

            }



            //increment the column counter
            columnCounter = columnCounter+1

            //if the column counter reaches the fifth column reset it and increase the row counter
            if (columnCounter >= 8) {
                columnCounter = 0
                rowCounter = rowCounter+1
            }




        } // end of the loop



    }

Answer 1

你说这是失败的，当你运行它第二次。这是因为您显然已经将rowCounter和columnCounter声明为属性，而且每次调用layoutCards()时都不会将rowCounter和columnCounter设置为0。

使rowCounter和columnCounter成为layoutCards()的局部变量

func layoutCards() {
    var rowCounter = 0
    var columnCounter = 0

    //  create cards array with several elements
    var cards = (1...64).map { _ in UIView() }// array with several cards