Xamarin iOS camera and photos - ios

Question

I am taking a picture with the iOS camera and trying to extract metadata from the image. This is my code:-
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, () => { });
}
protected void Handle_FinishedPickingMedia(object sender, UIImagePickerMediaPickedEventArgs e)
{
try
{
// determine what was selected, video or image
bool isImage = false;
switch (e.Info[UIImagePickerController.MediaType].ToString())
{
case "public.image":
isImage = true;
break;
}
// get common info
NSUrl referenceURL = e.Info[new NSString("UIImagePickerControllerReferenceURL")] as NSUrl;
if (referenceURL != null)
Console.WriteLine("Url:" + referenceURL.ToString());
I am able to initiate the camera, take the picture and then however when I click 'use photo'... The referenceURL comes back as NULL... How can I get the url, such that to extract GPS coordinates of the photo and such other attributes ?

Answer 1

I had a tremendous amount of trouble with the URL. It can be a file, it can be a web url and it acts different on every device. My app crashed and burned so many times with my test group. I finally found a way to get the Metadata from the data. There are multiple ways to get the DateTaken, Width and Height as well as GPS Coordinates. In addition, I needed the Camera MFG and the Model.
string dateTaken = string.Empty;
string lat = string.Empty;
string lon = string.Empty;
string width = string.Empty;
string height = string.Empty;
string mfg = string.Empty;
string model = string.Empty;
PHImageManager.DefaultManager.RequestImageData(asset, options, (data, dataUti, orientation, info) => {
dateTaken = asset.CreationDate.ToString();
// GPS Coordinates
var coord = asset.Location?.Coordinate;
if (coord != null)
{
lat = asset.Location?.Coordinate.Latitude.ToString();
lon = asset.Location?.Coordinate.Longitude.ToString();
}
UIImage img = UIImage.LoadFromData(data);
if (img.CGImage != null)
{
width = img.CGImage?.Width.ToString();
height = img.CGImage?.Height.ToString();
}
using (CGImageSource imageSource = CGImageSource.FromData(data, null))
{
if (imageSource != null)
{
var ns = new NSDictionary();
var imageProperties = imageSource.CopyProperties(ns, 0);
if (imageProperties != null)
{
width = ReturnStringIfNull(imageProperties[CGImageProperties.PixelWidth]);
height = ReturnStringIfNull(imageProperties[CGImageProperties.PixelHeight]);
var tiff = imageProperties.ObjectForKey(CGImageProperties.TIFFDictionary) as NSDictionary;
if (tiff != null)
{
mfg = ReturnStringIfNull(tiff[CGImageProperties.TIFFMake]);
model = ReturnStringIfNull(tiff[CGImageProperties.TIFFModel]);
//dateTaken = ReturnStringIfNull(tiff[CGImageProperties.TIFFDateTime]);
}
}
}
}
}
}
The little helper function
private string ReturnStringIfNull(NSObject inObj)
{
if (inObj == null) return String.Empty;
return inObj.ToString();
}

Answer 2

You can request a PHAsset from the reference Url and that will contain some metadata. You can request the image data to obtain more.
Note: If you need full EXIF, you need to check to ensure the image on on the device (could be iCloud-based), download it if needed, and then load the image data with the ImageIO framework (lots of SO postings cover this).
public void ImagePicker_FinishedPickingMedia(object sender, UIImagePickerMediaPickedEventArgs e)
{
void ImageData(PHAsset asset)
{
if (asset == null) throw new Exception("PHAsset is null");
PHImageManager.DefaultManager.RequestImageData(asset, null, (data, dataUti, orientation, info) =>
{
Console.WriteLine(data);
Console.WriteLine(info);
});
}
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).FirstOrDefault() as PHAsset;
ImageData(phAsset);
}
});
}
else
{
phAsset = PHAsset.FetchAssets(new[] { e.ReferenceUrl }, null).FirstOrDefault() as PHAsset;
ImageData(phAsset);
}
}
Note: Make sure you have request runtime photo library authorization PHPhotoLibrary.RequestAuthorization) and have set the Privacy - Photo Library Usage Description string in your info.plist to avoid a nasty privacy crash