ios_background_download.md

后台下载

参考

• 三种方式使得iOS应用能够在后台进行数据更新和下载

错误

iOS10在给downloadTask添加resumeData重新下载时，出现如下错误：

Invalid resume data for background download.

解决方法：stackoverflow

swift具体代码如下:

import UIKit

class ResumeDataTools: NSObject {
    
    func correct(requestData data: Data?) -> Data? {
        guard let data = data else {
            return nil
        }
        if NSKeyedUnarchiver.unarchiveObject(with: data) != nil {
            return data
        }
        guard let archive = (try? PropertyListSerialization.propertyList(from: data, options: [.mutableContainersAndLeaves], format: nil)) as? NSMutableDictionary else {
            return nil
        }
        // Rectify weird __nsurlrequest_proto_props objects to $number pattern
        var k = 0
        while ((archive["$objects"] as? NSArray)?[1] as? NSDictionary)?.object(forKey: "$\(k)") != nil {
            k += 1
        }
        var i = 0
        while ((archive["$objects"] as? NSArray)?[1] as? NSDictionary)?.object(forKey: "__nsurlrequest_proto_prop_obj_\(i)") != nil {
            let arr = archive["$objects"] as? NSMutableArray
            if let dic = arr?[1] as? NSMutableDictionary, let obj = dic["__nsurlrequest_proto_prop_obj_\(i)"] {
                dic.setObject(obj, forKey: "$\(i + k)" as NSString)
                dic.removeObject(forKey: "__nsurlrequest_proto_prop_obj_\(i)")
                arr?[1] = dic
                archive["$objects"] = arr
            }
            i += 1
        }
        if ((archive["$objects"] as? NSArray)?[1] as? NSDictionary)?.object(forKey: "__nsurlrequest_proto_props") != nil {
            let arr = archive["$objects"] as? NSMutableArray
            if let dic = arr?[1] as? NSMutableDictionary, let obj = dic["__nsurlrequest_proto_props"] {
                dic.setObject(obj, forKey: "$\(i + k)" as NSString)
                dic.removeObject(forKey: "__nsurlrequest_proto_props")
                arr?[1] = dic
                archive["$objects"] = arr
            }
        }
        /* I think we have no reason to keep this section in effect
         for item in (archive["$objects"] as? NSMutableArray) ?? [] {
         if let cls = item as? NSMutableDictionary, cls["$classname"] as? NSString == "NSURLRequest" {
         cls["$classname"] = NSString(string: "NSMutableURLRequest")
         (cls["$classes"] as? NSMutableArray)?.insert(NSString(string: "NSMutableURLRequest"), at: 0)
         }
         }*/
        // Rectify weird "NSKeyedArchiveRootObjectKey" top key to NSKeyedArchiveRootObjectKey = "root"
        if let obj = (archive["$top"] as? NSMutableDictionary)?.object(forKey: "NSKeyedArchiveRootObjectKey") as AnyObject? {
            (archive["$top"] as? NSMutableDictionary)?.setObject(obj, forKey: NSKeyedArchiveRootObjectKey as NSString)
            (archive["$top"] as? NSMutableDictionary)?.removeObject(forKey: "NSKeyedArchiveRootObjectKey")
        }
        // Reencode archived object
        let result = try? PropertyListSerialization.data(fromPropertyList: archive, format: PropertyListSerialization.PropertyListFormat.binary, options: PropertyListSerialization.WriteOptions())
        return result
    }
    
    func getResumeDictionary(_ data: Data) -> NSMutableDictionary? {
        // In beta versions, resumeData is NSKeyedArchive encoded instead of plist
        var iresumeDictionary: NSMutableDictionary? = nil
        if #available(iOS 10.0, OSX 10.12, *) {
            var root : AnyObject? = nil
            let keyedUnarchiver = NSKeyedUnarchiver(forReadingWith: data)
            
            do {
                root = try keyedUnarchiver.decodeTopLevelObject(forKey: "NSKeyedArchiveRootObjectKey") ?? nil
                if root == nil {
                    root = try keyedUnarchiver.decodeTopLevelObject(forKey: NSKeyedArchiveRootObjectKey)
                }
            } catch {}
            keyedUnarchiver.finishDecoding()
            iresumeDictionary = root as? NSMutableDictionary
            
        }
        
        if iresumeDictionary == nil {
            do {
                iresumeDictionary = try PropertyListSerialization.propertyList(from: data, options: PropertyListSerialization.ReadOptions(), format: nil) as? NSMutableDictionary;
            } catch {}
        }
        
        return iresumeDictionary
    }
    
    func correctResumeData(_ data: Data?) -> Data? {
        let kResumeCurrentRequest = "NSURLSessionResumeCurrentRequest"
        let kResumeOriginalRequest = "NSURLSessionResumeOriginalRequest"
        
        guard let data = data, let resumeDictionary = getResumeDictionary(data) else {
            return nil
        }
        
        resumeDictionary[kResumeCurrentRequest] = correct(requestData: resumeDictionary[kResumeCurrentRequest] as? Data)
        resumeDictionary[kResumeOriginalRequest] = correct(requestData: resumeDictionary[kResumeOriginalRequest] as? Data)
        
        let result = try? PropertyListSerialization.data(fromPropertyList: resumeDictionary, format: PropertyListSerialization.PropertyListFormat.xml, options: PropertyListSerialization.WriteOptions())
        return result
    }
    
    
    
    func correctedDownloadTask(withResumeData resumeData: Data, session: URLSession) -> URLSessionDownloadTask {
        let kResumeCurrentRequest = "NSURLSessionResumeCurrentRequest"
        let kResumeOriginalRequest = "NSURLSessionResumeOriginalRequest"
        
        let cData = correctResumeData(resumeData) ?? resumeData
        let task = session.downloadTask(withResumeData: cData)
        
        // a compensation for inability to set task requests in CFNetwork.
        // While you still get -[NSKeyedUnarchiver initForReadingWithData:]: data is NULL error,
        // this section will set them to real objects
        if let resumeDic = getResumeDictionary(cData) {
            if task.originalRequest == nil, let originalReqData = resumeDic[kResumeOriginalRequest] as? Data, let originalRequest = NSKeyedUnarchiver.unarchiveObject(with: originalReqData) as? NSURLRequest {
                task.setValue(originalRequest, forKey: "originalRequest")
            }
            if task.currentRequest == nil, let currentReqData = resumeDic[kResumeCurrentRequest] as? Data, let currentRequest = NSKeyedUnarchiver.unarchiveObject(with: currentReqData) as? NSURLRequest {
                task.setValue(currentRequest, forKey: "currentRequest")
            }
        }
        
        return task
    }

}