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;

 }