问题描述
我正在用Swift编写iOS应用。
在我的主页（ HomeLandingViewController.swift ）中，我必须调用两个并行的API，这给了我一张图像列表，我必须下载所有这些图像，然后转储到CoreData中。直到此过程完成，我必须在UI中显示一些加载动画等。
流量：
主页VC加载>开始动画>并行调用API 1和Call API 2>从API 1和API 2接收图像数组>获取所有这些图像的数据>转储到Coredata>通知主页VC完成>停止动画
为此，我制作了一个专用的类（ IconsHelper.swift ）
我正在使用Moya网络库。
问题在于事情没有按预期进行。由于事情是异步进行的，因此即使在下载图像之前，主页VC也会收到通知。
我的代码段：
IconsHelper.shared.getNewIconsFromServer()
class IconsHelper {
static let shared: IconsHelper = .init()
var group:dispatchGroup?
//Get Icons from API 1 and API 2:
func getNewIconsFromServer() {
group = dispatchGroup()
group?.enter()
let dispatchQueue_amc = dispatchQueue(label: "BackgroundIconsFetch_AMC",qos: .background)
dispatchQueue_amc.async(group: group) {
self.getNewIcons(type: .amcIcons)
}
if group?.hasGroupValue() ?? false {
group?.leave()
Log.b("CMSIcons: Group Leave 1")
}
group?.enter()
let dispatchQueue_bank = dispatchQueue(label: "BackgroundIconsFetch_Bank",qos: .background)
dispatchQueue_bank.async(group: group) {
self.getNewIcons(type: .bankIcons)
}
if group?.hasGroupValue() ?? false {
group?.leave()
Log.b("CMSIcons: Group Leave 2")
}
group?.notify(queue: .global(),execute: {
Log.b("CMSIcons: All icons fetched from server.")
})
}
func getNewIcons(type: CMSIconsTypes) {
let iconsCancellabletoken: Cancellabletoken?
let progressClosure: ProgressBlock = { response in
}
let activityChange: (_ change: NetworkActivityChangeType) -> Void = { (activity) in
}
let cmsCommonRequestType=self.getCmsCommonRequestType(type: type)
iconsCancellabletoken = CMSProvider<CMSCommonResponse>.request( .cmsCommonRequest(request: cmsCommonRequestType),success: { (_response) in
Log.b("CMSIcons: Get new icons from server for type: \(type)")
//Set http to https:
var iconsHostname:String=""{
didSet {
if let comps=URLComponents(string: iconsHostname) {
var _comps=comps
_comps.scheme = "https"
if let https = _comps.string {
iconsHostname=https
}
}
}
}
if (_response.data?.properties != nil) {
if _response.status {
let alias = self.getCmsAlias(type: type)
let property = _response.data?.properties.filter {$0.alias?.lowercased()==ValueHelper.getCMSAlias(alias)}.first?.value
if let jsonStr = property {
iconsHostname = _response.data?.hostName ?? ""
if let obj:CMSValuesResponse = CMSValuesResponse.map(JSONString: jsonStr) {
if let fieldsets=obj.fieldsets {
if fieldsets.count > 0 {
for index in 1...fieldsets.count {
let element=fieldsets[index-1]
if let prop = element.properties {
if(prop.count > 0) {
let urlAlias = self.getCmsURLAlias(type: type)
let iconUrl = prop.filter {$0.alias?.lowercased()==ValueHelper.getCMSAlias(urlAlias)}.first?.value
let name = prop.filter {$0.alias?.lowercased()==ValueHelper.getCMSAlias(.iconsNameAlias)}.first?.value
if let iconUrl=iconUrl,let name=name {
if let url = URL(string: iconsHostname+iconUrl) {
dispatchQueue.global().async {
if let data = try? Data(contentsOf: url) {
Log.b("CMSIcons: Icon url \(url.absoluteString) to Data done.")
var databaseDumpObject=CMSIconStructure()
databaseDumpObject.name=name
databaseDumpObject.data=data
self.dumpIconToLocalStorage(object: databaseDumpObject,type: type)
}
}
}
}
}
}
}//Loop ends.
//After success:
self.setFetchIconsDateStamp(type:type)
}
}
}
}
}
}
},error: { (error) in
},failure: { (_) in
},progress: progressClosure,activity: activityChange) as? Cancellabletoken
}
//Dump icon data into CoreData:
func dumpIconToLocalStorage(object: CMSIconStructure,type: CMSIconsTypes) {
let entityName = self.getEntityName(type: type)
if #available(iOS 10.0,*) {
Log.b("Do CoreData task in background thread")
//Do CoreData task in background thread:
let context = appDelegate().persistentContainer.viewContext
let privateContext: NSManagedobjectContext = {
let moc = NSManagedobjectContext(concurrencyType: .privateQueueConcurrencyType)
moc.parent = context
return moc
}()
//1: Read all offline Icons:
let fetchRequest = NSFetchRequest<NSFetchRequestResult>(entityName: entityName)
fetchRequest.predicate = nspredicate(format: "name = %@",argumentArray: [object.name.lowercased()])
do {
let results = try privateContext.fetch(fetchRequest) as? [NSManagedobject]
if results?.count != 0 {
//2: Icon already found in CoreData:
if let icon=results?[0] {
icon.setValue(object.name.lowercased(),forKey: "name") //save lowercased
icon.setValue(object.data,forKey: "data")
}
} else {
//3: Icon not found in CoreData:
let entity = NSEntityDescription.entity(forEntityName: entityName,in: privateContext)
let newIcon = NSManagedobject(entity: entity!,insertInto: privateContext)
newIcon.setValue(object.name.lowercased(),forKey: "name") //save lowercased
newIcon.setValue(object.data,forKey: "data")
}
Log.b("CMSIcons: Icon data saved locally against name: \(object.name)")
} catch {
Log.i("Failed reading CoreData \(entityName.uppercased()). Error: \(error)")
}
privateContext.perform {
// Code in here is Now running "in the background" and can safely
// do anything in privateContext.
// This is where you will create your entities and save them.
do {
try privateContext.save()
} catch {
Log.i("Failed reading CoreData \(entityName.uppercased()). Error: \(error)")
}
}
} else {
// Fallback on earlier versions
}
}
}
解决方法
通常不建议将图像作为二进制数据存储在Core Data持久存储中。而是将图像写入本地目录，然后将本地URL存储在核心数据中。这是一个示例工作流程，可以使用此推荐方法简化您遇到的一些问题：
class IconsHelper {
let container: NSPersistentContainer
let provider: CMSProvider<CMSCommonResponse>
private let queue: DispatchQueue = DispatchQueue(label: "IconsHelper",qos: .userInitiated)
let documentsDirectory: URL = {
let searchPath = NSSearchPathForDirectoriesInDomains(.documentDirectory,.userDomainMask,true)
guard let path = searchPath.last else {
preconditionFailure("Unable to locate users documents directory.")
}
return URL(fileURLWithPath: path)
}()
init(container: NSPersistentContainer,provider: CMSProvider<CMSCommonResponse>) {
self.container = container
self.provider = provider
}
enum Icon: String,Hashable {
case amc
case bank
}
func getIcons(_ icons: Set<Icon>,dispatchQueue: DispatchQueue = .main,completion: @escaping ([Icon: URL]) -> Void) {
queue.async {
var results: [Icon: URL] = [:]
guard icons.count > 0 else {
dispatchQueue.async {
completion(results)
}
return
}
let numberOfIcons = icons.count
var completedIcons: Int = 0
for icon in icons {
let request = [""] // Create request for the icon
self.provider.request(request) { (result) in
switch result {
case .failure(let error):
// Do something with the error
print(error)
completedIcons += 1
case .success(let response):
// Extract information from the response for the icon
let imageData: Data = Data() // the image
let localURL = self.documentsDirectory.appendingPathComponent(icon.rawValue + ".png")
do {
try imageData.write(to: localURL)
try self.storeURL(localURL,forIcon: icon)
results[icon] = localURL
} catch {
print(error)
}
completedIcons += 1
if completedIcons == numberOfIcons {
dispatchQueue.async {
completion(results)
}
}
}
}
}
}
}
func storeURL(_ url: URL,forIcon icon: Icon) throws {
// Write the local URL for the specific icon to your Core Data Container.
let context = container.newBackgroundContext()
// Locate & modify,or create CMSIconStructure using the context above.
try context.save()
}
}
然后在您的首页视图控制器中：
// Display Animation
let helper: IconsHelper = IconsHelper.init(container: /* NSPersistentContainer */,provider: /* API Provider */)
helper.getIcons([.amc,.bank]) { (results) in
// Process Results
// Hide Animation
}
这里的一般设计是只有一个调用，该调用将处理图像的下载和处理，然后在所有网络调用和核心数据交互完成之后响应结果。
在示例中，您将使用对CoreData NSPersistentContainer和网络实例的引用来初始化IconsHelper。这种方法是否有助于弄清为什么示例代码无法按预期方式工作？