File 获取URL Objective-C处的文件大小

我正在寻找一种方法来获取NSURL地址处特定文件的文件大小。这是我尝试过的，但它总是在日志输出中返回“0”：

NSString *url = @"http://www.examplesite.com/file01.zip";

unsigned long long fileSize1 = [[[NSFileManager defaultManager] attributesOfItemAtPath:[url lastPathComponent] error:nil] fileSize];
NSLog(@"size of %@ in bytes === %llu", [url lastPathComponent], fileSize1);

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在搜索了一些之后，我找到了这个解决方案。它在服务器上查找文件大小，并在日志中显示结果

NSString *url = @"http://www.examplesite.com/file01.zip";
                NSURL *URL = [NSURL URLWithString:url];
                NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:URL];
                [request setHTTPMethod:@"HEAD"];
                NSHTTPURLResponse *response;
                [NSURLConnection sendSynchronousRequest:request returningResponse:&response error: nil];
                long long size = [response expectedContentLength];
                NSLog(@"File size before download: %lld",size);

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在搜索了一些之后，我找到了这个解决方案。它在服务器上查找文件大小，并在日志中显示结果

NSString *url = @"http://www.examplesite.com/file01.zip";
                NSURL *URL = [NSURL URLWithString:url];
                NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:URL];
                [request setHTTPMethod:@"HEAD"];
                NSHTTPURLResponse *response;
                [NSURLConnection sendSynchronousRequest:request returningResponse:&response error: nil];
                long long size = [response expectedContentLength];
                NSLog(@"File size before download: %lld",size);