NSURLSessionDownloadTask 下载文件

 -(void)RequestdataUI:(NSString*)ImageURL

            imageName:(NSString*)imageName{

     NSURL *url = [NSURL URLWithString:ImageURL];

     NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:url];

     //创建对象的同时 后台会开启一个新的线程去发出请求了

     NSURLSession *session = [NSURLSession sharedSession];

     NSURLSessionDownloadTask *DownloadTask = [session downloadTaskWithRequest:request

                                                             completionHandler:^(NSURL *location, NSURLResponse *response,NSError *error) {

         // 输出下载文件原来的存放目录

         NSLog(@"%@", location);

         // 设置文件的存放目标路径

         NSString *documentsPath = [self getDocumentsPath];

         NSURL *documentsDirectoryURL = [NSURL fileURLWithPath:documentsPath];

         NSURL *fileURL = [documentsDirectoryURL URLByAppendingPathComponent:[[response URL]lastPathComponent]];

         // 如果该路径下文件已经存在，就要先将其移除，在移动文件

         NSFileManager *fileManager = [NSFileManager defaultManager];

         if ([fileManager fileExistsAtPath:[fileURL path] isDirectory:NULL]) {

             [fileManager removeItemAtURL:fileURL error:NULL];

         }

         [fileManager moveItemAtURL:location toURL:fileURL error:NULL];

         //--------创建plist文件-----------

         NSString *plistPath = [documentsPath stringByAppendingPathComponent:@"imagePath.plist"];

         NSMutableDictionary *PathPlist= [[[NSMutableDictionary alloc]initWithContentsOfFile:plistPath]mutableCopy];

         if (PathPlist==nil) {

             PathPlist = [[NSMutableDictionary alloc ] init];

         }

         [PathPlist setObject:imageName forKey:ImageURL];

         [PathPlist writeToFile:plistPath atomically:YES ];

     }];

     [DownloadTask resume];

 }

 - (NSString *)getDocumentsPath {

     NSArray *documents = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory,NSUserDomainMask, YES);

     NSString *documentsPath = documents[];

     NSString* ImagePath =[documentsPath stringByAppendingPathComponent:@"DownloadImage"];

     //文件管理器

     NSFileManager *fileManager = [NSFileManager defaultManager];

     //新建文件夹

     [fileManager createDirectoryAtPath:ImagePath withIntermediateDirectories:YES attributes:nil error:nil];

     return ImagePath;

 }