在集合视图中预加载 MKMapView

Question

我正在尝试 "tab" 体验。每个选项卡都有屏幕宽度，用户可以在每个选项卡之间滑动。一切正常，除了在索引为“3”的选项卡上实现了 MKMapView。

当用户打开应用程序时，集合视图被初始化为索引“1”，同时 cellForIndexAtIndexPath 被调用 IndexPath(row: 1, section: 0)

override func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell
{
    let cell = collectionView.dequeueReusableCell(withReuseIdentifier: PageIndentifier, for: indexPath) as! TabCell

    if (indexPath.item == 0)
    {
        cell.SetupNearestView()
        NearestView = cell.nearestView
        NearestView?.Delegate = self
    }

    if (indexPath.item == 1)
    {
        cell.SetupStationsView()
        StationsView = cell.stationsView
        StationsView?.Delegate = self
    }

    if (indexPath.item == 2)
    {
        cell.SetupMapView()
        MapView = cell.stationsMapView
    }

    return cell
}

问题是，当用户从 1 -> 2 滑动时，UI 被阻止大约一秒钟，然后为 IndexPath(row: 2, section: 0) 调用集合视图触发器 cellForIndexAtIndexPath。我在该索引处尝试 "force" 称重传感器，但不幸的是，地图似乎在渲染到屏幕之前就被初始化了。有什么解决方法吗？

编辑：

TabCell.swift

class TabCell : UICollectionViewCell
{
var nearestView : NearestView?
var stationsView : StationsView?
var stationsMapView : MapView?

override init(frame: CGRect)
{
    super.init(frame: frame)

    let gradient = CAGradientLayer()
    gradient.frame = bounds
    gradient.colors = [UIColor.clear, RuntimeResources.Get(color: .VeryDarkBlue).cgColor]
    layer.insertSublayer(gradient, at: 0)
}

required init?(coder aDecoder: NSCoder)
{
    fatalError("init(coder:) has not been implemented")
}

func SetupNearestView()
{
    if (nearestView != nil)
    {
        return
    }

    nearestView = NearestView(frame: CGRect(x: 0, y: 0, width: frame.width, height: frame.height))
    addSubview(nearestView!)

    addConstraintsWithFormat(format: "H:|[v0]|", views: nearestView!)
    addConstraintsWithFormat(format: "V:|[v0]|", views: nearestView!)

}

func SetupMapView()
{
    if (stationsMapView != nil)
    {
        return
    }

    stationsMapView = MapView(frame: CGRect(x: 0, y: 0, width: frame.width, height: frame.height))
    addSubview(stationsMapView!)

    addConstraintsWithFormat(format: "H:|[v0]|", views: stationsMapView!)
    addConstraintsWithFormat(format: "V:|[v0]|", views: stationsMapView!)
}

func SetupStationsView()
{
    if (stationsView != nil)
    {
       return
    }

    stationsView = StationsView(frame: CGRect(x: 0, y: 0, width: frame.width, height: frame.height))
    addSubview(stationsView!)

    addConstraintsWithFormat(format: "H:|[v0]|", views: stationsView!)
    addConstraintsWithFormat(format: "V:|[v0]|", views: stationsView!)
}
}

MapView.swift

import UIKit
import MapKit

class MapView: MKMapView, MKMapViewDelegate
{
private let infoViewHeight = CGFloat(500)
private let FocusZoomLevel = 0.01
private let ZoomLevel = 0.04
private let centerOfSzczecin = CLLocationCoordinate2D(latitude: 53.433345, longitude: 14.544139)
private var infoViewTopConstraint : NSLayoutConstraint?

lazy var mainStationView : UIView = {

    let msv = UIView(frame: CGRect(x: 0, y: 0, width: self.frame.width, height: self.infoViewHeight))
    msv.translatesAutoresizingMaskIntoConstraints = false
    msv.backgroundColor = RuntimeResources.Get(color: .DarkBlue)
    return msv
}()

override init(frame: CGRect)
{
    super.init(frame: frame)
    delegate = self

    // Adding info view
    SetupInfoView()

    // Setting center of map
    let span = MKCoordinateSpanMake(ZoomLevel, ZoomLevel)
    let region = MKCoordinateRegion(center: centerOfSzczecin, span: span)
    setRegion(region, animated: false)
}

required init?(coder aDecoder: NSCoder)
{
    fatalError("init(coder:) has not been implemented")
}

private func SetupInfoView()
{
    addSubview(mainStationView)
    infoViewTopConstraint = mainStationView.topAnchor.constraint(equalTo: self.bottomAnchor)
    infoViewTopConstraint?.isActive = true
    mainStationView.leftAnchor.constraint(equalTo: self.leftAnchor).isActive = true
    mainStationView.rightAnchor.constraint(equalTo: self.rightAnchor).isActive = true
    mainStationView.heightAnchor.constraint(equalToConstant: infoViewHeight).isActive = true
}

}

Answer 1

因为您没有重复使用 MapView 单元格。

尝试将您的 mapView 作为变量 outside 加载到 UICollectionViewCell（在您的 UIViewController 中）并将其作为子视图添加到 collectionView:willDisplayCell:forItemAtIndexPath:

在 collectionView:didEndDisplayingCell:forItemAtIndexPath: 中，您可以将其从单元格中删除。

只需在单元格外加载所有 mapView 代码，然后使用 Cell 将地图显示为子视图即可。

在集合视图中预加载 MKMapView

Preloading MKMapView in collection view

mkmapview

ios

uicollectionview

uicollectionviewcell

swift