Ios AF3.0下载任务。下载内存中的数据总是会导致内存爆炸

AF3.0下载任务。下载内存中的数据总是会导致内存爆炸

NSURLSessionConfiguration *configuration = [NSURLSessionConfiguration defaultSessionConfiguration];
AFURLSessionManager *manager = [[AFURLSessionManager alloc] initWithSessionConfiguration:configuration];

NSURL *URL = [NSURL URLWithString:@"http://dlsw.baidu.com/sw-search-sp/soft/9d/25765/sogou_mac_32c_V3.2.0.1437101586.dmg"];

NSURLRequest *request = [NSURLRequest requestWithURL:URL];

_downloadTask = [manager downloadTaskWithRequest:request progress:^(NSProgress * _Nonnull downloadProgress) {

    dispatch_async(dispatch_get_main_queue(), ^{

        [progressview setProgress:downloadProgress.fractionCompleted animated:YES];

        dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(0.3 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{

            str=[NSString stringWithFormat:@"%.2f",downloadProgress.fractionCompleted*100];
            lab.text=str;

        });
    });
} destination:^NSURL * _Nonnull(NSURL * _Nonnull targetPath, NSURLResponse * _Nonnull response) {
    NSURL *documentsDirectoryURL = [[NSFileManager defaultManager] URLForDirectory:NSDocumentDirectory inDomain:NSUserDomainMask appropriateForURL:targetPath create:NO error:nil];
    return [documentsDirectoryURL URLByAppendingPathComponent:[response suggestedFilename]];
} completionHandler:^(NSURLResponse * _Nonnull response, NSURL * _Nullable filePath, NSError * _Nullable error) {
    NSLog(@"File downloaded to: %@", filePath);

}];