[image_picker] Fix image_picker Hanging After Attempting to Open Unavailable Camera on iOS Simulator

[chgibb]

Description

This PR resolves the description given in the title. image_picker hangs on iOS simulator after being rejected for the camera being unavailable.

Related Issues

flutter/flutter #18095 describes very similar behaviour, except with respect to the gallery and video picker.
flutter/plugins #595 introduced the FLTImagePickerPlugin#imagePickerControllerDidCancel method, however it is never actually called anywhere in the code base. This PR simply makes use of it.

Checklist

• I read the Contributor Guide and followed the process outlined there for submitting PRs.
• My PR includes unit or integration tests for all changed/updated/fixed behaviors (See Contributor Guide).
• All existing and new tests are passing.
• I updated/added relevant documentation (doc comments with ///).
• The analyzer (flutter analyze) does not report any problems on my PR.
• I read and followed the Flutter Style Guide.
• The title of the PR starts with the name of the plugin surrounded by square brackets, e.g. [shared_preferences]
• I updated pubspec.yaml with an appropriate new version according to the pub versioning philosophy.
• I updated CHANGELOG.md to add a description of the change.
• I signed the CLA.
• I am willing to follow-up on review comments in a timely manner.

Breaking Change

Does your PR require plugin users to manually update their apps to accommodate your change?

• Yes, this is a breaking change (please indicate a breaking change in CHANGELOG.md and increment major revision).
• No, this is not a breaking change.

[cyanglaz]

I believe the imagePickerControllerDidCancel is a delegate method in the UIImagePickerControllerDelegate so it should be called by the system when the image picker is cancelled.
I feel like this issue can be fixed by bringing the below code outside of the camera authorization check.

 if ([UIImagePickerController isSourceTypeAvailable:UIImagePickerControllerSourceTypeCamera]) {
   _imagePickerController.sourceType = UIImagePickerControllerSourceTypeCamera;
   [_viewController presentViewController:_imagePickerController animated:YES completion:nil];
 } else {
   [[[UIAlertView alloc] initWithTitle:@"Error"
                               message:@"Camera not available."
                              delegate:nil
                     cancelButtonTitle:@"OK"
                     otherButtonTitles:nil] show];
 }

[chgibb]

A full search for the name returns no results except the declaration. As for factoring out the code you showed, what exactly do you propose? I am only passingly familiar with Objective-C.

[cyanglaz]

@chgibb no worries. So OBJC has a delegation pattern. Basically our ImagePickerPlugin conform to the UIImagePickerControllerDelegate protocol. One of the method in the protocol is imagePickerControllerDidCancel. So the iOS framework is calling [UIImagePickerControllerDelegate imagePickerControllerDidCancel] somewhere. Delegate methods are not usually meant to be called manually.
That said, my hunch is that the issue is that we didn't check the camera availability before checking the camera authorization. We were checking the availability after authorization. See showCamera.
So ideally, if we move this logic that i posted outside and check the camera availability first, then check the authorization, we might be able to fix the issue.

[chgibb]

@cyanglaz I believe that fundamentally, a result is not being returned in the event that the camera is not available. The else branch after the check for availability displays a dialog alerting the use that the camera is not available but does not return a result back to Flutter. Adding

self.result(nil);
self.result = nil;
_arguments = nil;

immediately following the "Camera not available" dialog also appears to resolve the issue. I realize that is simply the method body of the didCancel delegate, but it was my understanding that lines 122-124 already checked for camera availability.

[cyanglaz]

Adding

self.result(nil);
self.result = nil;
_arguments = nil;

makes much more sense! Do you mind to update the PR with this change?

[chgibb]

@cyanglaz absolutely! I will make the change on Monday and ping you again for review and approval. I appreciate the timely and kind discussion and feedback!

[chgibb]

Made the change @cyanglaz .

[cyanglaz]

@chadidi CI seems not happy about some formatting, do you mind reformat?