The image attached is just "Attachment-1", no extension. How do I specify one ?
NSData *compressedImage = UIImageJPEGRepresentation(self.resultImage, 0.8 );
UIActivityViewController *activityViewController = [[UIActivityViewController alloc] initWithActivityItems:@[ @"Check this out!", compressedImage ] applicationActivities:nil];
[self.navigationController presentViewController:activityViewController animated:YES completion:nil];
According to this answer you should be able to use this workaround to specify a filename
The obvious drawback of this approach is that you will have to save the image on disk.
Credit to timeuser's suggestion, converting UIImage to NSData.