iOS Xamarin Attaching a picture to the Email Body - Null Exception - ios

Question

I am using my first Xamarin iOS app to take a picture, extract meta data of the picture, attach the picture to an email body and send email.
// (1.) Take a photo with the Camera //
partial void BtnCamera_TouchUpInside(UIButton sender)
{
UIImagePickerController imagePicker = new UIImagePickerController();
imagePicker.PrefersStatusBarHidden();
imagePicker.SourceType = UIImagePickerControllerSourceType.Camera;
// handle saving picture and extracting meta-data from picture //
imagePicker.FinishedPickingMedia += Handle_FinishedPickingMedia;
// present //
PresentViewController(imagePicker, true, () => { });
}
// (2.) Saves the image to the phone and then extracts metadata //
protected void Handle_FinishedPickingMedia(object sender, UIImagePickerMediaPickedEventArgs e)
{
//NSUrl url = null;
try
{
#region Save Image and Get Meta-data
// Save Image before processing for meta-data //
SaveImagetoPhone(e);
// Get meta-data from saved image //
GetImageMetaData(e);
// (3.) Save picture to the phone and extract photo url //
private static void SaveImagetoPhone(UIImagePickerMediaPickedEventArgs e)
{
NSUrl url = null;
void ImageData(PHAsset asset)
{
if (asset == null)
throw new Exception("PHAsset is null");
PHImageManager.DefaultManager.RequestImageData(asset, null, (data, dataUti, orientation, info) =>
{
url = info.ValueForKey(new NSString("PHImageFileURLKey")) as NSUrl;
PhotoDataClass._file = url.Path;
}); }
PHAsset phAsset;
if (e.ReferenceUrl == null)
{
e.OriginalImage?.SaveToPhotosAlbum((image, error) =>
{
if (error == null)
{
var options = new PHFetchOptions
{
FetchLimit = 1,
SortDescriptors = new[] { new NSSortDescriptor("creationDate", true) }
};
phAsset = PHAsset.FetchAssets(options).LastOrDefault() as PHAsset;
ImageData(phAsset);
}
});
}
else
{
phAsset = PHAsset.FetchAssets(new[] { e.ReferenceUrl }, null).FirstOrDefault() as PHAsset;
ImageData(phAsset);
}
}
At this point I have successfully extracted the URL for the file:-
"/var/mobile/Media/DCIM/100APPLE/IMG_0036.JPG"
However when I run my email function, even though the url is populated, I get a null exception without any explanation that I know of.
// (4.) Email functionality //
https://developer.xamarin.com/recipes/ios/shared_resources/email/send_an_email/
partial void BtnMessageDone_TouchUpInside(UIButton sender)
{
MFMailComposeViewController mailController;
if (MFMailComposeViewController.CanSendMail)
{
StringBuilder htmlBodyMail = FormatEmailBody();
mailController = new MFMailComposeViewController();
// do mail operations here
mailController.SetToRecipients(new string[] { "xxx.yy#email.com" });
mailController.SetSubject("mail test");
mailController.SetMessageBody(htmlBodyMail.ToString(), false);
UIImage img = UIImage.FromFile(PhotoDataClass._file);
mailController.AddAttachmentData(img.AsJPEG(), "image/JPG", "Image.JPG");
mailController.Finished += (object s, MFComposeResultEventArgs args) =>
{
Console.WriteLine(args.Result.ToString());
args.Controller.DismissViewController(true, null);
};
this.PresentViewController(mailController, true, null);
}
}
The null exception occurs on the line inside the email functionality:-
mailController.AddAttachmentData(img.AsJPEG(), "image/JPG", "Image.JPG");

Answer 1

From your code, the image will be null when you use UIImage img = UIImage.FromFile(PhotoDataClass._file);. So this null exception will be thrown.
We should use PHAsset to retrieve image from system photo library instead of using the url directly. You can store the LocalIdentifier to the class PhotoDataClass, then retrieve the PHAsset through this identifier when you want to use it later.
Modify the ImageData method:
void ImageData(PHAsset asset)
{
if (asset == null)
throw new Exception("PHAsset is null");
PhotoDataClass.AssetIdentifier = asset.LocalIdentifier;
}
Then BtnMessageDone_TouchUpInside method can be:
MFMailComposeViewController mailController;
if (MFMailComposeViewController.CanSendMail)
{
var results = PHAsset.FetchAssetsUsingLocalIdentifiers(new string[] { PhotoDataClass.AssetIdentifier }, null);
foreach (PHAsset asset in results)
{
if (asset.LocalIdentifier == PhotoDataClass.AssetIdentifier)
{
PHImageManager.DefaultManager.RequestImageData(asset, null, (data, dataUti, orientation, info) =>
{
StringBuilder htmlBodyMail = FormatEmailBody();
mailController = new MFMailComposeViewController();
// do mail operations here
...
UIImage img = UIImage.LoadFromData(data);
mailController.AddAttachmentData(img.AsJPEG(), "image/JPG", "Image.JPG");
...
});
}
}
}
Moreover That LastOrDefault() is not what I think it is
This is because your NSSortDescriptor, use SortDescriptors = new[] { new NSSortDescriptor("creationDate", false) } or phAsset = PHAsset.FetchAssets(options).FirstOrDefault() as PHAsset; to get your photo you just capture from your camera.