iOS NSURLSessionDownloadTask 报错 Invalid resume data for background download. Bac

错误： Invalid resume data for background download. Background downloads must use http or https and must download to an accessible file.

网上好多说这个错误在ios10中出现，如果调试的时候，点暂停下载，再重新发布到手机上，再点击开始下载，也会有这个错误。

解决办法：自定义一个NSURLSession分类，在ios10代替- (NSURLSessionDownloadTask *)downloadTaskWithResumeData:(NSData *)resumeData;

NSURLSession+TYCorrectedResumeData.h

#import 

@interface NSURLSession (TYCorrectedResumeData)

- (NSURLSessionDownloadTask *)downloadTaskWithCorrectResumeData:(NSData *)resumeData;

@end

NSURLSession+TYCorrectedResumeData.m

//
//  NSURLSession+TYCorrectedResumeData.m
//  TYDownloadManagerDemo
//
//  Created by tanyang on 2016/10/7.
//  Copyright © 2016年 tany. All rights reserved.
//

#import "NSURLSession+TYCorrectedResumeData.h"
#import 

#define IS_IOS10ORLATER ([[[UIDevice currentDevice] systemVersion] floatValue] >= 10)

@implementation NSURLSession (TYCorrectedResumeData)

- (NSURLSessionDownloadTask *)downloadTaskWithCorrectResumeData:(NSData *)resumeData {
    NSString *kResumeCurrentRequest = @"NSURLSessionResumeCurrentRequest";
    NSString *kResumeOriginalRequest = @"NSURLSessionResumeOriginalRequest";
    
    NSData *cData = correctResumeData(resumeData);
    cData = cData?cData:resumeData;
    NSURLSessionDownloadTask *task = [self downloadTaskWithResumeData:cData];
    NSMutableDictionary *resumeDic = getResumeDictionary(cData);
    if (resumeDic) {
        if (task.originalRequest == nil) {
            NSData *originalReqData = resumeDic[kResumeOriginalRequest];
            NSURLRequest *originalRequest = [NSKeyedUnarchiver unarchiveObjectWithData:originalReqData ];
            if (originalRequest) {
                [task setValue:originalRequest forKey:@"originalRequest"];
            }
        }
        if (task.currentRequest == nil) {
            NSData *currentReqData = resumeDic[kResumeCurrentRequest];
            NSURLRequest *currentRequest = [NSKeyedUnarchiver unarchiveObjectWithData:currentReqData];
            if (currentRequest) {
                [task setValue:currentRequest forKey:@"currentRequest"];
            }
        }
        
    }
    return task;
}

#pragma mark- private

NSData * correctRequestData(NSData *data) {
    if (!data) {
        return nil;
    }
    // return the same data if it's correct
    if ([NSKeyedUnarchiver unarchiveObjectWithData:data] != nil) {
        return data;
    }
    NSMutableDictionary *archive = [[NSPropertyListSerialization propertyListWithData:data options:NSPropertyListMutableContainersAndLeaves format:nil error:nil] mutableCopy];
    
    if (!archive) {
        return nil;
    }
    NSInteger k = 0;
    id objectss = archive[@"$objects"];
    while ([objectss[1] objectForKey:[NSString stringWithFormat:@"$%ld",k]] != nil) {
        k += 1;
    }
    NSInteger i = 0;
    while ([archive[@"$objects"][1] objectForKey:[NSString stringWithFormat:@"__nsurlrequest_proto_prop_obj_%ld",i]] != nil) {
        NSMutableArray *arr = archive[@"$objects"];
        NSMutableDictionary *dic = arr[1];
        id obj = [dic objectForKey:[NSString stringWithFormat:@"__nsurlrequest_proto_prop_obj_%ld",i]];
        if (obj) {
            [dic setValue:obj forKey:[NSString stringWithFormat:@"$%ld",i+k]];
            [dic removeObjectForKey:[NSString stringWithFormat:@"__nsurlrequest_proto_prop_obj_%ld",i]];
            [arr replaceObjectAtIndex:1 withObject:dic];
            archive[@"$objects"] = arr;
        }
        i++;
    }
    if ([archive[@"$objects"][1] objectForKey:@"__nsurlrequest_proto_props"] != nil) {
        NSMutableArray *arr = archive[@"$objects"];
        NSMutableDictionary *dic = arr[1];
        id obj = [dic objectForKey:@"__nsurlrequest_proto_props"];
        if (obj) {
            [dic setValue:obj forKey:[NSString stringWithFormat:@"$%ld",i+k]];
            [dic removeObjectForKey:@"__nsurlrequest_proto_props"];
            [arr replaceObjectAtIndex:1 withObject:dic];
            archive[@"$objects"] = arr;
        }
    }
    // Rectify weird "NSKeyedArchiveRootObjectKey" top key to NSKeyedArchiveRootObjectKey = "root"
    if ([archive[@"$top"] objectForKey:@"NSKeyedArchiveRootObjectKey"] != nil) {
        [archive[@"$top"] setObject:archive[@"$top"][@"NSKeyedArchiveRootObjectKey"] forKey: NSKeyedArchiveRootObjectKey];
        [archive[@"$top"] removeObjectForKey:@"NSKeyedArchiveRootObjectKey"];
    }
    // Reencode archived object
    NSData *result = [NSPropertyListSerialization dataWithPropertyList:archive format:NSPropertyListBinaryFormat_v1_0 options:0 error:nil];
    return result;
}

NSMutableDictionary *getResumeDictionary(NSData *data) {
    NSMutableDictionary *iresumeDictionary = nil;
    if (IS_IOS10ORLATER) {
        id root = nil;
        id  keyedUnarchiver = [[NSKeyedUnarchiver alloc] initForReadingWithData:data];
        @try {
            root = [keyedUnarchiver decodeTopLevelObjectForKey:@"NSKeyedArchiveRootObjectKey" error:nil];
            if (root == nil) {
                root = [keyedUnarchiver decodeTopLevelObjectForKey:NSKeyedArchiveRootObjectKey error:nil];
            }
        } @catch(NSException *exception) {
            
        }
        [keyedUnarchiver finishDecoding];
        iresumeDictionary = [root mutableCopy];
    }
    
    if (iresumeDictionary == nil) {
        iresumeDictionary = [NSPropertyListSerialization propertyListWithData:data options:NSPropertyListMutableContainersAndLeaves format:nil error:nil];
    }
    return iresumeDictionary;
}

NSData *correctResumeData(NSData *data) {
    NSString *kResumeCurrentRequest = @"NSURLSessionResumeCurrentRequest";
    NSString *kResumeOriginalRequest = @"NSURLSessionResumeOriginalRequest";
    if (data == nil) {
        return  nil;
    }
    NSMutableDictionary *resumeDictionary = getResumeDictionary(data);
    if (resumeDictionary == nil) {
        return nil;
    }
    resumeDictionary[kResumeCurrentRequest] = correctRequestData(resumeDictionary[kResumeCurrentRequest]);
    resumeDictionary[kResumeOriginalRequest] = correctRequestData(resumeDictionary[kResumeOriginalRequest]);
    NSData *result = [NSPropertyListSerialization dataWithPropertyList:resumeDictionary format:NSPropertyListXMLFormat_v1_0 options:0 error:nil];
    return result;
}

@end