我正在尝试基于Advanced ScrollView Techniques from WWDC 2011实现无限分页的UIScrollView。 Im面临的问题是，当我滚动屏幕时，屏幕会一直向后跳转，而不是在数组中前进。有什么办法可以产生这种效果。下面是我到目前为止已实现的代码。
import Foundation
import UIKit
class CustomScrollView:UIScrollView{
var label1:CustomLabel!
var label2:CustomLabel!
var label3:CustomLabel!
var labels:[UILabel]!
var visibleLabels:[UILabel]!
var recycledPages:Set<CustomLabel>!
var visiblePages:Set<CustomLabel>!
override init(frame: CGRect) {
super.init(frame: frame)
indicatorStyle = .white
recycledPages = Set<CustomLabel>()
visiblePages = Set<CustomLabel>()
var firstScreenPostion:CGRect = CGRect(origin: CGPoint(x: 0 * bounds.width, y: 0), size: bounds.size)
var secondeScreenPosition:CGRect = CGRect(origin: CGPoint(x: 1 * bounds.width, y: 0), size: bounds.size)
var thirdScreenPosition:CGRect = CGRect(origin: CGPoint(x: 2 * bounds.width, y: 0), size: bounds.size)
label1 = CustomLabel(frame: firstScreenPostion)
label1.backgroundColor = .red
label1.text = "1"
label2 = CustomLabel(frame: secondeScreenPosition)
label2.backgroundColor = .green
label2.text = "2"
label3 = CustomLabel(frame: thirdScreenPosition)
label3.backgroundColor = .blue
label3.text = "3"
visibleLabels = [label1,label2,label3]
labels = [label1,label2,label3]
}
required init?(coder aDecoder: NSCoder) {
fatalError("init(coder:) has not been implemented")
}
func recenterIfNecessary(){
let currentOffset = contentOffset
let contentWidth = contentSize.width
let centerOffset = (contentWidth - bounds.width)/2
let distanceFromCenter = abs(currentOffset.x - centerOffset)
if distanceFromCenter > contentWidth/4{
self.contentOffset = CGPoint(x: centerOffset, y: 0)
for label in visibleLabels{
var center = label.center
center.x += centerOffset - currentOffset.x
label.center = center
}
}
}
override func layoutSubviews() {
recenterIfNecessary()
let visibleBounds = bounds
let minimumVisibleX = bounds.minX
let maximumVisbleX = bounds.maxX
tilePages(minimumVisibleX: minimumVisibleX, toMaxX: maximumVisbleX)
// tileLabelsFromMinX(minimumVisibleX: minimumVisibleX, toMaxX: maximumVisbleX)
}
func insertLabel()->UILabel{
let recycledLabels = visibleLabels.filter { (label) -> Bool in
return label.superview == nil
}
let label = recycledLabels.last ?? UILabel(frame: bounds)
self.addSubview(label)
return label
}
func placeNewLabelOnRight(rightEdge: CGFloat)->CGFloat{
let label = self.insertLabel()
visibleLabels.append(label) // add rightmost label at the end of the array
label.frame.origin.x = rightEdge;
label.frame.origin.y = 0
label.text = labels.last?.text
return label.frame.maxX
}
func placeNewLabelOnLeft(leftEdge:CGFloat)->CGFloat{
let label = self.insertLabel()
self.visibleLabels.insert(label, at: 0) // add leftmost label at the beginning of the array
label.frame.origin.x = leftEdge - frame.size.width;
label.frame.origin.y = bounds.size.height - frame.size.height;
label.text = labels[0].text
return label.frame.minX
}
//function used in video
// func tileLabelsFromMinX(minimumVisibleX:CGFloat, toMaxX maximumVisibleX:CGFloat){
// // the upcoming tiling logic depends on there already being at least one label in the visibleLabels array, so
// // to kick off the tiling we need to make sure there's at least one label
// if (self.visibleLabels.count == 0)
// {
// self.placeNewLabelOnRight(rightEdge: minimumVisibleX);
// }
// print("visible labels.count: \(visibleLabels.count)")
//
// // add labels that are missing on right side
// // UILabel *lastLabel = [self.visibleLabels lastObject];
// var lastLabel = visibleLabels.last!
// var rightEdge = lastLabel.frame.maxX
// while (rightEdge < maximumVisibleX){
// rightEdge = self.placeNewLabelOnRight(rightEdge: rightEdge)
// }
//
// // add labels that are missing on left side
// var firstLabel = self.visibleLabels[0]
// var leftEdge = firstLabel.frame.minX
// while (leftEdge > minimumVisibleX){
// leftEdge = self.placeNewLabelOnLeft(leftEdge:leftEdge)
// }
//
// // remove labels that have fallen off right edge
// // lastLabel = [self.visibleLabels lastObject];
//
// while (lastLabel.frame.origin.x > maximumVisibleX){
// lastLabel.removeFromSuperview()
// self.visibleLabels.removeLast()
// lastLabel = self.visibleLabels.last!
// }
//
// // remove labels that have fallen off left edge
// firstLabel = self.visibleLabels[0];
// while (firstLabel.frame.maxX < minimumVisibleX){
// firstLabel.removeFromSuperview()
// self.visibleLabels.removeFirst()
// firstLabel = self.visibleLabels[0];
// }
// }
func tilePages(minimumVisibleX:CGFloat, toMaxX maximumVisibleX:CGFloat){
let visibleBounds = bounds
var firstNeededPageIndex:Int = Int(floorf(Float(minimumVisibleX/visibleBounds.width)))
var lastNeededPageIndex:Int = Int(floorf(Float((maximumVisibleX - 1)/visibleBounds.width)))
firstNeededPageIndex = max(firstNeededPageIndex, 0)
lastNeededPageIndex = min(lastNeededPageIndex, labels.count - 1)
//Recycle no-longer needed pages
for page in visiblePages{
if page.index < Int(firstNeededPageIndex) || page.index > Int(lastNeededPageIndex){
recycledPages.insert(page)
page.removeFromSuperview()
}
}
visiblePages.subtract(recycledPages)
//add missing pages
for i in firstNeededPageIndex...lastNeededPageIndex{
if !isDisplaying(pageForIndex: i){
let page:CustomLabel = dequeueRecycledPage() ?? CustomLabel()
print("index i: \(i)")
self.configurePage(page: page, forIndex: i)
self.addSubview(page)
visiblePages.insert(page)
}
}
}
func isDisplaying(pageForIndex index:Int)->Bool{
for page in visiblePages{
if page.index == index{
return true
}
}
return false
}
func configurePage(page:CustomLabel,forIndex index:Int){
page.index = index
page.text = "current index: \(index)"
let width = bounds.width
let newX:CGFloat = CGFloat(index) * width
page.backgroundColor = labels[index].backgroundColor
page.frame = CGRect(origin: CGPoint(x: newX, y: 0), size: bounds.size)
}
func dequeueRecycledPage()->CustomLabel?{
let page = recycledPages.first
if let page = page{
recycledPages.remove(page)
return page
}
return nil
}
}