How to set crop information for `thumbnailImageData` of CNMutableContact - ios

Question

I create/update contacts, using CNMutableContact.
I can set new image via imageData property, but I need to set custom crop information for creating thumbnail. Property thumbnailImageData is read-only.
Code:
let cnContact = CNMutableContact()
cnContact.imageData = imageData //created before
How to add custom thumbnailImage crop?

Answer 1

It seems that setting a thumbnail is not possible in iOS. However, by definition, a thumbnail of an image is the same image cropped to a smaller dimension. Hence iOS will auto generate the thumbnail from the image data set on the contact while saving the contact.
If you want to setup a different images for thumbnail and actual contact image, iOS will not allow you to do this.
Problem I have:
Before adding a new contact (CNMutableContact reference) in the user's contacts, I want to display the contact to the user. I can use the imageData to setup the new contact's image. However, when using CNContactViewController to display this new contact, the image is not cropped as per thumbnail. The thumbnail image showed looks super weird and scaled. How to resolve this?
Solution:
This occurs because the thumbnailImageData property on the CNMutableContact object is nil. This property cannot be set by the developers. This property can only be set by iOS internals and is auto generated by iOS while saving the contact.
So, before displaying the CNMutableContact object, you should save it to the users contacts, to kick in the auto-thumbnail-generation, and then immediately delete the contact.
The following extension on CNMutableContact depicts what you can do to achieve this.
extension CNMutableContact {
func generateThumbnailImage() {
if self.thumbnailImageData != nil {
return
}
// contact.thumbnailImageData is nil
// First save the contact for the thumbnail to be generated
let saveRequest = CNSaveRequest()
saveRequest.add(self, toContainerWithIdentifier: nil)
do {
try CNContactStore().execute(saveRequest)
} catch let error {
print("Error occurred while saving the request \(error)")
}
// self.thumbnailImageData is not nil. Contact Store will generate the thumbnail for this contact with the imageData provided.
// Now delete the contact
let deleteRequest = CNSaveRequest()
deleteRequest.delete(self)
do {
try CNContactStore().execute(deleteRequest)
} catch let error {
print("Error occurred while deleting the request \(error)")
}
// The contact is removed from the Contact Store
// However, the contact.thumbnailImageData is not nil anymore. Contacts Store has generated the thumbnail automatically with the imageData provided.
}
}