NSURL *url = [NSURL fileURLWithPath:@"/Users/xiaomage/Desktop/test.png"];
NSURLRequest *request = [NSURLRequest requestWithURL:url];
// 第一种
[NSURLConnection sendAsynchronousRequest:request queue:[NSOperationQueue mainQueue] completionHandler:^(NSURLResponse *response, NSData *data, NSError *connectionError) {
NSLog(@"%@", response.MIMEType);
}];
// 第二种
NSURLResponse *response = nil;
[NSURLConnection sendSynchronousRequest:request returningResponse:&response error:nil];
NSLog(@"%@", response.MIMEType);
