如何使用swift实现表视图中图像的延迟加载?

I want to use lazy loading concept for my table view using swift. In my table view i am showing multiple cells which contain product images and product name . Please help me to get the solution.

我想使用swift为我的表视图使用惰性加载概念。在我的表视图中，我展示了包含产品图像和产品名称的多个单元格。请帮我找到解决办法。

3 个解决方案

#1

Old Solution:

旧的解决方案:

Since you doesn't show any code.

因为你没有显示任何代码。

Here is the example for you.

这里有一个例子。

func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell {

    // try to reuse cell
    let cell:CustomCell = tableView.dequeueReusableCellWithIdentifier("DealCell") as CustomCell

    // get the deal image
    let currentImage = deals[indexPath.row].imageID
    let unwrappedImage = currentImage
    var image = self.imageCache[unwrappedImage]
    let imageUrl = NSURL(string: "http://staging.api.cheapeat.com.au/deals/\(unwrappedImage)/photo")

    // reset reused cell image to placeholder
    cell.dealImage.image = UIImage(named: "placeholder")

    // async image
    if image == nil {

    let request: NSURLRequest = NSURLRequest(URL: imageUrl!)

    NSURLConnection.sendAsynchronousRequest(request, queue: NSOperationQueue.mainQueue(), completionHandler: {(response: NSURLResponse!,data: NSData!,error: NSError!) -> Void in
        if error == nil {

            image = UIImage(data: data)

            self.imageCache[unwrappedImage] = image
            dispatch_async(dispatch_get_main_queue(), {
                cell.dealImage.image = image

            })
        }
        else {

        }
    })
    }

    else{
        cell.dealImage.image = image
    }

  return cell

}

Follow THIS tutorial for more Info. Hope this will help you.

更多信息请跟随本教程。希望这能对你有所帮助。

New Solution:

新的解决方案:

Here is extension for it which is created by my friend Leo Dabus which is really simple to use:

这是我的朋友Leo Dabus做的扩展，非常简单:

extension UIImageView {
    func downloadImageFrom(link link:String, contentMode: UIViewContentMode) {
        NSURLSession.sharedSession().dataTaskWithURL( NSURL(string:link)!, completionHandler: {
            (data, response, error) -> Void in
            dispatch_async(dispatch_get_main_queue()) {
                self.contentMode =  contentMode
                if let data = data { self.image = UIImage(data: data) }
            }
        }).resume()
    }
}

Now in your cellForRowAtIndexPath method assign image to cell this way:

现在，在cellForRowAtIndexPath方法中，将图像分配给单元格:

cell.cellImageView.image = UIImage(named: "placeholder")  //set placeholder image first.
cell.cellImageView.downloadImageFrom(link: imageLinkArray[indexPath.row], contentMode: UIViewContentMode.ScaleAspectFit)  //set your image from link array.

And as Rob suggested into comment here is some useful libraries which you can use:

正如Rob所建议的，这里有一些有用的库，你可以使用:

1. https://github.com/Alamofire/AlamofireImage
2. https://github.com/Alamofire/AlamofireImage
3. https://github.com/onevcat/Kingfisher
4. https://github.com/onevcat/Kingfisher
5. https://github.com/rs/SDWebImage
6. https://github.com/rs/SDWebImage
7. https://github.com/kean/DFImageManager
8. https://github.com/kean/DFImageManager

#2

Since I can't comment just yet, here's a Swift 3 (Xcode 8 Beta 6) version of the useful extension provided by Leo Dabus.

由于我还不能对此做出评论，下面是由Leo Dabus提供的Swift 3 (Xcode 8 Beta 6)版本的有用扩展。

extension UIImageView {
    func downloadImageFrom(link:String, contentMode: UIViewContentMode) {
        URLSession.shared.dataTask( with: NSURL(string:link)! as URL, completionHandler: {
            (data, response, error) -> Void in
            DispatchQueue.main.async {
                self.contentMode =  contentMode
                if let data = data { self.image = UIImage(data: data) }
            }
        }).resume()
    }
}

I'm using this inside a class that populates the table cell, it works like this in that context just fine, just in case any newbs were wondering if it will:

我在填充表格单元格的类中使用这个，它在那种情况下工作得很好，以防任何newbs想知道它是否会:

albumArt.image = UIImage(named: "placeholder")
albumArt.downloadImageFrom(link: "http://someurl.com/image.jpg", contentMode: UIViewContentMode.scaleAspectFit)

#3

Task

Async image loading in tableViewCell in swift 3 using SDWebImage.

在swift 3中使用SDWebImage在tableViewCell中异步加载图像。

Details

xCode 8.3.1, swift 3.1

xCode 8.3.1,斯威夫特3.1

Full sample

Info.plist (add value)

信息。plist(增值)

<key>NSAppTransportSecurity</key>
<dict>
    <key>NSAllowsArbitraryLoads</key>
    <true/>
</dict>

Podfile

Podfile

 platform :ios, '8.0'
 use_frameworks!

 target '*-28694645' do
    pod 'Alamofire'
    pod 'ObjectMapper'
    pod 'SDWebImage'
 end

NetworkManager

使其

import Foundation
import Alamofire

// data loader
class NetworkManager {

    class func request(string: String, block: @escaping ([String: Any]?)->()) {
        Alamofire.request(string).responseJSON { response in

            if let result = response.result.value as? [String: Any] {
                block(result)
            } else {
                block(nil)
            }
        }
    }
}

ItunceItem

ItunceItem

import Foundation
import ObjectMapper

class ItunceItem: Mappable {
    var wrapperType: String?
    var imageUrlString:String?

    required convenience init?(map: Map) {
        self.init()
    }

    private func unwrapedDescription(value: Any?) -> String {
        if let value = value {
            return "\(value)"
        }
        return "[no data]"
    }

    var description: String {
        var _result = ""
        _result += " imageUrlString: \(unwrapedDescription(value: imageUrlString))\n"
        _result += " wrapperType: \(unwrapedDescription(value: wrapperType))\n"
        _result += " price: "

        return _result
    }

    func mapping(map: Map) {
        wrapperType         <- map["wrapperType"]
        imageUrlString      <- map["artworkUrl100"]
    }
}

TableViewCell

TableViewCell

import UIKit

class TableViewCell: UITableViewCell {

    @IBOutlet weak var artworkImageView: UIImageView!
}

ViewController

ViewController

import UIKit
import SDWebImage

class ViewController: UIViewController {

    @IBOutlet weak var tableView: UITableView!
    fileprivate var items = [ItunceItem]()
    fileprivate var viewControlerInited = false

    override func viewDidLoad() {
        super.viewDidLoad()
        tableView.dataSource = self
        tableView.delegate = self
        tableView.tableFooterView = UIView()
        reloadData()
    }

    override func viewDidAppear(_ animated: Bool) {
        super.viewDidAppear(animated)
        viewControlerInited = true
    }

    override func viewWillDisappear(_ animated: Bool) {
        super.viewWillDisappear(animated)
        disableDownloadingAllImages()
    }
}


// MARK: - Different

extension ViewController {

    fileprivate func reloadData() {

        NetworkManager.request(string: "https://itunes.apple.com/search?term=navigator") {  [weak self] json in
            if let _self = self {
                if let json = json, let array = json["results"] as? [[String:Any]] {
                    var result = [ItunceItem]()
                    for item in array {
                        if let itunceItem = ItunceItem(JSON: item) {
                            result.append(itunceItem)
                        }
                    }
                    _self.items = result
                    _self.tableView.reloadData()
                }
            }
        }
    }

    fileprivate func disableDownloadingAllImages() {
        SDWebImageDownloader.shared().cancelAllDownloads()
    }

    fileprivate func reloadImages() {

        for cell in tableView.visibleCells {
            if let indexPath = tableView.indexPath(for: cell) {
                let cell = cell as! TableViewCell
                if let imageUrlString = items[indexPath.row].imageUrlString, let url = URL(string: imageUrlString) {
                    cell.artworkImageView.sd_cancelCurrentAnimationImagesLoad()
                    cell.artworkImageView.sd_setImage(with: url)
                }
            }
        }

    }
}

// MARK: - UITableViewDataSource

extension ViewController: UITableViewDataSource {

    func numberOfSections(in tableView: UITableView) -> Int {
        return 1
    }

    public func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
        return items.count
    }

    func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
        let cell = tableView.dequeueReusableCell(withIdentifier: "TableViewCell") as! TableViewCell
        return cell
    }
}

// MARK: - UITableViewDelegate

extension ViewController: UITableViewDelegate {

    func tableView(_ tableView: UITableView, willDisplay cell: UITableViewCell, forRowAt indexPath: IndexPath) {
        let cell = cell as! TableViewCell
        if let imageUrlString = items[indexPath.row].imageUrlString, let url = URL(string: imageUrlString) {
            cell.artworkImageView.sd_setImage(with: url)
        }
    }

    func tableView(_ tableView: UITableView, didEndDisplaying cell: UITableViewCell, forRowAt indexPath: IndexPath) {
        let cell = cell as! TableViewCell
        cell.artworkImageView.sd_cancelCurrentImageLoad()
    }
}

Main.storyboard

Main.storyboard

<?xml version="1.0" encoding="UTF-8"?>
<document type="com.apple.InterfaceBuilder3.CocoaTouch.Storyboard.XIB" version="3.0" toolsVersion="12120" systemVersion="16E195" targetRuntime="iOS.CocoaTouch" propertyAccessControl="none" useAutolayout="YES" useTraitCollections="YES" colorMatched="YES" initialViewController="BYZ-38-t0r">
    <device id="retina4_7" orientation="portrait">
        <adaptation id="fullscreen"/>
    </device>
    <dependencies>
        <deployment identifier="iOS"/>
        <plugIn identifier="com.apple.InterfaceBuilder.IBCocoaTouchPlugin" version="12088"/>
        <capability name="Constraints to layout margins" minToolsVersion="6.0"/>
        <capability name="documents saved in the Xcode 8 format" minToolsVersion="8.0"/>
    </dependencies>
    <scenes>
        <!--View Controller-->
        <scene sceneID="tne-QT-ifu">
            <objects>
                <viewController id="BYZ-38-t0r" customClass="ViewController" customModule="*_28694645" customModuleProvider="target" sceneMemberID="viewController">
                    <layoutGuides>
                        <viewControllerLayoutGuide type="top" id="y3c-jy-aDJ"/>
                        <viewControllerLayoutGuide type="bottom" id="wfy-db-euE"/>
                    </layoutGuides>
                    <view key="view" contentMode="scaleToFill" id="8bC-Xf-vdC">
                        <rect key="frame" x="0.0" y="0.0" width="375" height="667"/>
                        <autoresizingMask key="autoresizingMask" widthSizable="YES" heightSizable="YES"/>
                        <subviews>
                            <tableView clipsSubviews="YES" contentMode="scaleToFill" alwaysBounceVertical="YES" dataMode="prototypes" style="plain" separatorStyle="default" rowHeight="130" sectionHeaderHeight="28" sectionFooterHeight="28" translatesAutoresizingMaskIntoConstraints="NO" id="cY7-zo-hDK">
                                <rect key="frame" x="0.0" y="20" width="375" height="647"/>
                                <color key="backgroundColor" white="1" alpha="1" colorSpace="calibratedWhite"/>
                                <prototypes>
                                    <tableViewCell clipsSubviews="YES" contentMode="scaleToFill" selectionStyle="default" indentationWidth="10" reuseIdentifier="TableViewCell" id="HDb-wV-LQ8" customClass="TableViewCell" customModule="*_28694645" customModuleProvider="target">
                                        <rect key="frame" x="0.0" y="28" width="375" height="130"/>
                                        <autoresizingMask key="autoresizingMask"/>
                                        <tableViewCellContentView key="contentView" opaque="NO" clipsSubviews="YES" multipleTouchEnabled="YES" contentMode="center" tableViewCell="HDb-wV-LQ8" id="Gky-9l-DJ9">
                                            <rect key="frame" x="0.0" y="0.0" width="375" height="129.5"/>
                                            <autoresizingMask key="autoresizingMask"/>
                                            <subviews>
                                                <imageView userInteractionEnabled="NO" contentMode="scaleAspectFill" horizontalHuggingPriority="251" verticalHuggingPriority="251" translatesAutoresizingMaskIntoConstraints="NO" id="YX7-DV-Qnj">
                                                    <rect key="frame" x="137" y="14" width="100" height="100"/>
                                                    <constraints>
                                                        <constraint firstAttribute="width" constant="100" id="p8R-if-uRk"/>
                                                    </constraints>
                                                </imageView>
                                            </subviews>
                                            <constraints>
                                                <constraint firstItem="YX7-DV-Qnj" firstAttribute="centerY" secondItem="Gky-9l-DJ9" secondAttribute="centerY" id="Lg1-9u-aL6"/>
                                                <constraint firstItem="YX7-DV-Qnj" firstAttribute="top" secondItem="Gky-9l-DJ9" secondAttribute="topMargin" constant="6" id="kqB-PW-PE1"/>
                                                <constraint firstItem="YX7-DV-Qnj" firstAttribute="centerX" secondItem="Gky-9l-DJ9" secondAttribute="centerX" id="lKR-7v-WtO"/>
                                            </constraints>
                                        </tableViewCellContentView>
                                        <connections>
                                            <outlet property="artworkImageView" destination="YX7-DV-Qnj" id="spC-sk-Al3"/>
                                        </connections>
                                    </tableViewCell>
                                </prototypes>
                            </tableView>
                        </subviews>
                        <color key="backgroundColor" red="1" green="1" blue="1" alpha="1" colorSpace="custom" customColorSpace="sRGB"/>
                        <constraints>
                            <constraint firstItem="cY7-zo-hDK" firstAttribute="top" secondItem="y3c-jy-aDJ" secondAttribute="bottom" id="J7x-rb-aus"/>
                            <constraint firstItem="cY7-zo-hDK" firstAttribute="leading" secondItem="8bC-Xf-vdC" secondAttribute="leading" id="Zgh-3u-vEw"/>
                            <constraint firstItem="cY7-zo-hDK" firstAttribute="bottom" secondItem="wfy-db-euE" secondAttribute="top" id="v68-ej-1ne"/>
                            <constraint firstAttribute="trailing" secondItem="cY7-zo-hDK" secondAttribute="trailing" id="ywW-Jl-d9z"/>
                        </constraints>
                    </view>
                    <connections>
                        <outlet property="tableView" destination="cY7-zo-hDK" id="6rX-DT-7Va"/>
                    </connections>
                </viewController>
                <placeholder placeholderIdentifier="IBFirstResponder" id="dkx-z0-nzr" sceneMemberID="firstResponder"/>
            </objects>
            <point key="canvasLocation" x="-76" y="116.49175412293854"/>
        </scene>
    </scenes>
</document>

Result