NSFetchedResultsController object deleted from UITableView on update - ios

Please be gentle, this is my first ever post.
When I update a subclassed NSManagedObject and perform a save using a fetched results controller, instead of calling NSFetchedResultsChangeUpdate in "didChangeObject" it calls NSFetchedResultsChangeDelete. The save works and it updates the objects, but then immediately deletes it from the UITableView. If I quit and return, the object re-appears in the tableview with the updates so I know it is saving it to the DB.
I am developing code for a simple task app using XCODE 5. I am using an iPhone 4S and not the simulator to test it. It was working fine until I made some mods to another part of the code (I thought unconnected and now it doesn't work.
I have a sort order and when I update an object and it changed in the sort order, there was a nice animation for the moving of the UITableViewCells....now I have to force a fetch again and do [self.tableView reloadData]. This is a hack as I do not get any animations, but it is the only way I can get it to update:
I have a prepare for segue method:
- (void) prepareForSegue: (UIStoryboardSegue *) segue sender: (id) sender
{
// configure the destination view controller:
if ( [segue.destinationViewController isKindOfClass: [ShowEditTaskTableViewController class]])
{
if ([sender isKindOfClass:[UITableViewCell class]] )
{
NSIndexPath *indexPath = [self.taskTableView indexPathForCell:sender];
[self.taskTableView deselectRowAtIndexPath:indexPath animated:YES];
// Pass the selected task to the new view controller.
ShowEditTaskTableViewController *detailViewController = segue.destinationViewController;
Task *info = [self.fetchedResultsController objectAtIndexPath:indexPath];
detailViewController.editedObject = info;
}
else
{
NSIndexPath *indexPath = [self.taskTableView indexPathForCell:sender];
[self.taskTableView deselectRowAtIndexPath:indexPath animated:YES];
ShowEditTaskTableViewController *detailViewController = segue.destinationViewController;
Task *info = (Task *)[NSEntityDescription insertNewObjectForEntityForName:#"Task" inManagedObjectContext:self.managedObjectContext];
detailViewController.editedObject = info;
}
}
}
There is nothing special here. "Task" is my NSManagedObject.
I have a rewind (EDIT: changed reverse to rewind after comment) segue and before it is called, I set the variables which will be set stored in the editedObject.:
- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender
{
if ([segue.identifier isEqualToString:#"addNewTaskSave"]) {
// Note: This is an unwind segue to go back to the previous screen.
self.dueDate = self.taskDatePicker.date;
self.description = self.taskDescriptionTextView.text;
self.priority = self.taskPrioritySegment.selectedSegmentIndex;
}
}
and in the RootViewController it calls:
- (IBAction)addNewTaskSave:(UIStoryboardSegue *)segue
{
ShowEditTaskTableViewController *controller = segue.sourceViewController;
controller.editedObject.shortDesc = controller.description;
controller.editedObject.priority = #(controller.priority);
controller.editedObject.dueDate = controller.dueDate;
controller.editedObject.completed = #0;
NSError *error;
if (![self.managedObjectContext save:&error]) {
...
}
.....
}
It uses the standard didChangeObject delegate methods. This worked fine until I clearly changed something.
Now after the save, it sets the NSFetchedResultsChangeDelete option and deletes the table row.
The fix is to add:
self.fetchedResultsController = nil;
if (![[self fetchedResultsController] performFetch:&error]) {
...
}
[self.taskTableView reloadData];
However, this means that what is actually observed is just a straight update of the Table View with no animation.
Without this code, you can observe an animated delete of the table row. If I quit and restart, my edited object is there.
I have scoured SO which has been my constant companion for the last 4 weeks (the time I have been coding for IOS) and cannot find anything on this behaviour.
Any help would be greatly appreciated.
EDIT:
before the save, controller.editedObject isDeleted = NO, isUpdated = YES, so I can't see why it is setting NSFetchedResultsControllerChangeDelete.

I'm just going to discuss one piece of your code; and this may not have anything to do with the fetch results controller issue described.
Your so-called unwind/reverse segue has me stumped. I don't think prepareForSegue:sender: is relevant for an official unwind segue. So maybe you're not really using an official unwind segue (which is created by control-dragging from a button to the "exit" icon beneath a storyboard scene).
Unless you're referring to an unwind segue, there's no such thing as a "reverse" segue that takes you back to a previous screen. A push segue, for example, doesn't have a separate counterpart called a "pop" segue.
I suspect that you have segues crisscrossing between two scenes in storyboard. In other words, you created a segue from scene A to scene B, and you created a segue from scene B to scene A. If that's really the case, I would avoid doing that because it's unconventional. Maybe spend some time reviewing segues.
Ok, so I'll briefly address the fetched results controller issue. If there are user-driven changes to the data in a table view populated by a fetched results controller, then you will need to set a flag and temporarily "turn off" the fetched results controller delegate methods. This issue is mentioned briefly in the docs for NSFetchedResultsControllerDelegate protocol under "User-Driven Updates".

It appears my scouring of SO was not very good. see here https://stackoverflow.com/a/18998335/3482632
I added a UISegmentControl to filter and used the int value of its segment index.
int index = self.filterSegment.selectedSegmentIndex;
NSPredicate *predicate = [NSPredicate predicateWithFormat:[NSString stringWithFormat:#"filter == %d", index]];
[fetchRequest setPredicate:predicate];
"filter" in my NSManagedObject subclass is an NSNumber. when I changed the NSPredicate to
NSPredicate *predicate = [NSPredicate predicateWithFormat:[NSString stringWithFormat:#"filter == %#", #(index)]];
everything works fine.

Related

Xcode: Why is my NSLog getting called twice?

I have an ID for a post from my server that I would like to access in two different view controllers. The first view controller is a table view that displays the posts. The user will select a row and the ID for that post will be passed to the next view controller to display details about the post. I use the code below.
-(void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath {
PFObject *objectId = [collectionArray objectAtIndex:indexPath.row];
selectedObjectID = [objectId objectId];
self.objectID = [objectId objectId];
[self performSegueWithIdentifier:#"details" sender:self];
}
-(void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender {
if ([segue.identifier isEqual: #"details"]) {
PreviewDetailsViewController *details = (PreviewDetailsViewController *)[segue destinationViewController];
details.objectID = self.objectID;
}
}
"selectedObjectID" is an extern variable and "self.objectID" is a property I set for both classes and tried to set it in the prepareForSegue method. Both of these ways of doing it do the same thing. It passes the variable to the next view controller but when I
NSLog(#"object = %#", self.objectID);
or
NSLog(#"object = %#", selectedObjectID);
in the viewDidLoad of the next view controller, it passes the ID to the next view controller, but it logs out this
object = (null)
object = Zz81bHEeJD
It's like it is getting called twice and the call that matters when I try to query for "self.objectID" or "selectedObjectID" I get
*** Terminating app due to uncaught exception 'NSInvalidArgumentException',
reason: 'Cannot do a comparison query for type: (null)'
which is causing me much headache.
Can anyone explain to me what is going on here and how I can rectify this?
viewDidLoad gets called when your view controller is loaded. When you are in prepareForSegue, you know that the view controller has already been loaded - because you are able to get a reference to it from destinationViewController. This means that viewDidLoad executes before you assign a value to details.objectId.
You should access the property in a method such as viewWillAppear, or trigger your query in a custom setter for the objectId property on your PreviewDetailsViewController.
And I assume that the extern was just for testing, but don't use externs

Custom setter for segue not seeing the object I'm sending to it in iPhone Master/Detail storyboard

Basically, I'm trying to send an object from the master view to the detail view by way of a custom setter. However, as soon as the setter gets called in the detail view, the app immediately crashes. I'm not too good at debugging, but I think it's because the object isn't making it to the setter -- it's seeing it as nil. Could be wrong about that, though.
Here's the code for the segue in the master view:
- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender
{
if ([[segue identifier] isEqualToString:#"showDetail"]) {
NSIndexPath *indexPath = [self.tableView indexPathForSelectedRow];
CCNewsItem *theNewsItem = self.listOfNewsItems[indexPath.row];
NSLog(#"Preparing to pass: %#", theNewsItem);
[[segue destinationViewController] setSelectedNewsItem:theNewsItem];
}
}
And here it is for the setter in the detail view:
- (void)setSelectedNewsItem:(CCNewsItem *)newItem
{
if (self.selectedNewsItem != newItem) {
self.selectedNewsItem = newItem;
// Update the view.
[self configureView];
}
}
It crashes exactly on the - (void)setSelectedNewsItem:(CCNewsItem *)newItem line. I've made super-sure that the object being passed is valid (I log it to double check, and all seems well), but it seems that it either isn't making it to the setter or it's somehow exploding when it hits it.
Any ideas? Thanks!
As requested, here's the logs/exception
This is what my NSLog shows on the object I'm trying to pass:
2013-11-02 14:18:23.660 Curtis Consulting[14862:60b] Preparing to pass: <CCNewsItem: 0x14e70580>
When the app stops on the setter's first line (I'm not sure why; I have all breakpoints disabled), it shows the values of newItem (the passed object) as:
newItem CCNewsItem * nil 0x00000000
NSObject NSObject
_headline NSString * nil
_body NSString * nil
_url NSURL * nil
Edit 2
Since, as near as I can tell, there is no way to copy the error it's showing (in a green bar at the right, but I don't have any breakpoints turned on), here's my transcription of it:
Thread 1: EXC_BAD_ACCESS (code=2, address=0x27c84ff8)
In your setter method change:
if (self.selectedNewsItem != newItem) {
self.selectedNewsItem = newItem;
to
if (_selectedNewsItem != newItem) {
_selectedNewsItem = newItem;
Because your current code has an infinite loop calling the accessor method. Be sure you know what using self. means...

Delete existing data from another view

I trying to build app like native Apple Notes. And I have a question\problem.
In apple notes when you open already existing note again and delete all text from it - note deleting and data from core data deleting too. How can I do it? First view of app - List of notes, and second view - note. I can't understand how delete that object, what I need. For example: when my segue from list to note look like that:
-(void) prepareForSegue:(UIStoryBoardSegue *)segue sender:(id)sender{
NoteDetailVC *destViewController = segue.destinationViewController;
if([[segue identifier] isEqualToString:#"ShowNote"]){
NSManagedObject *selectedNote = [self.notes objectAtIndex[[self.tableView indexPathForSelectedRow] row]];
destViewController.selectedNoteInfo = selectedNote;
}
}
And in NoteDetailVC I interact with data some like that:
if (selectedNoteInfo){
// bla bla bla code
}
On create I use setValue: command and else. I understand how dismiss controller without saving data before I set new value. But don't understand how delete already existing object from core data. How check what index I need and etc? Help please! :-)
And sorry for my English again :)
Here is the approach I would take, given I am understanding your question correctly.
When the user chooses to create a new note, create your NSManagedObject to represent that.
Note *newNote = [NSEntityDescription insertNewObjectForEntityForName:#"Note" inManagedObjectContext:self.context];
When they go back to the list or press Done... In prepareForSegue:sender: check the contents of the note.
if (note.contents.length == 0) {
[self.context deleteObject:note];
}
[self.context save:&error]

How can I return to a view without creating repeating versions of the same view?

I have a split view where the top section of my split shows some questions, and the bottom section shows some other stuff. The problem is that I had it written to "push" to a new view every time the user selects a question. This is obviously less than ideal because the user can enter a situation where they have 15 copies (more or less, depending on how many times the user selects a question) of the same question to go back through.
I thought that a simple solution would be to set a BOOL for when a user selects a question, but as it turns out, this introduces a new bug where the user can select a question once, but if they go back they are out of luck. I'm kind of stuck here, and any guidance would be greatly appreciated.
Program flow:
First you need to understand a little about what I am trying to do. I am building a historical inquiry app that focuses on allowing teachers to support student learning of historical inquiry. As such, there are core questions as well as documents the students can analyze.
Based on the way the app has come along, JSLDetailViewController displays the core questions and JSL_QuestionInteraction displays the questions for analyzing the documents.
Relevant code snippet:
-(void) tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath {
if(indexPath.section == 0){
if(!didSelectQuestion){
[self performSegueWithIdentifier:#"questionDisplaySegue" sender:indexPath];
didSelectQuestion = TRUE;
} else {
JSLDetailViewController *detailView = [JSLDetailViewController alloc];
detailView.telegram = indexPath.row;
[detailView setDetailItem:indexPath];
}
}else if(indexPath.section == 1){
[self performSegueWithIdentifier:#"telegramQuestionDisplaySegue" sender:indexPath];
JSL_QuestionInteraction *questionView = [[JSL_QuestionInteraction alloc] init];
questionView.managedObjectContext = self.managedObjectContext;
}
}
-(void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender{
if([segue.identifier isEqualToString:#"questionDisplaySegue"]){
JSLDetailViewController *detailView = (JSLDetailViewController *)segue.destinationViewController;
detailView.telegram = index.row;
[detailView setDetailItem:index];
JSLDetailViewController *controller = (JSLDetailViewController *)segue.destinationViewController;
controller.managedObjectContext = self.managedObjectContext;
} else if ([segue.identifier isEqualToString:#"telegramQuestionDisplaySegue"]){
JSL_QuestionInteraction *questionView = [[JSL_QuestionInteraction alloc] init];
questionView.managedObjectContext = self.managedObjectContext;
}
}
Please let me know if you need any additional details to understand this problem.
I don't know if any of what I write here will fix your problem because I still don't really understand your structure, but I see a couple of things wrong in your posted code.
First, when you're doing segues you shouldn't be alloc init'ing anything in code, the segue instantiates the new controllers for you. It's not clear what you're doing with detailView in didSelectRowAtIndexPath:, you do an alloc with no init -- you should never ever do an alloc without an init. If that detailView is something that's already present on screen, you should get a reference to that instance and set telegram and detailItem on that.
In the "if" clause of prepareForSegue you are assigning the segue.destinationViewController to two different local variables, detailView and controller -- they both point to the same thing, so there's no reason to have them both.
In the "else" clause, once again your alloc init'ing a controller, which you shouldn't do. You probably want to get the segue's destination view controller instead.

Memory management using ARC on iOS

Just have a quickly question (more of a curiosity thing) based on a problem I just solved (I will post the answer to my problem in the post, which can be found here: My former question
The thing is that I have this UITableView which contains custom cell objects. Every time you enter this view, I generate new cells for the UITableView like this:
if (cell == nil)
{
[[NSBundle mainBundle] loadNibNamed:#"UploadCellView" owner:self options:nil];
cell = customCell;
}
Which happens in the standard method:
-(UITableViewCell*)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
Now the problem is that my custom cell objects listens for NSNotifications about upload objects happening in the background, so they can update its model data to their labels and progress bars etc. It happens like this (this is a method from the custom cell objects):
-(void) uploadProgress: (NSNotification*)notification
{
NSDictionary *userInfo = [notification userInfo];
NSNumber *uploadID = [userInfo valueForKey:#"uploadID"];
if (uploadID.integerValue == uploadActivity.uploadID)
{
UIProgressView *theProgressBar = (UIProgressView*)[self viewWithTag:progressBarTag];
[theProgressBar setProgress:(uploadActivity.percentageDone / 100) animated:YES];
UILabel *statusText = (UILabel*)[self viewWithTag:percentageTag];
[statusText setText:[NSString stringWithFormat:#"Uploader - %.f%% (%.01fMB ud af %.01fMB)", uploadActivity.percentageDone, uploadActivity.totalMBUploaded, uploadActivity.totalMBToUpload]];
}
}
When an upload finish they simply do this:
-(void) uploadFinished: (NSNotification*)notification
{
NSDictionary *userInfo = [notification userInfo];
NSNumber *uploadID = [userInfo valueForKey:#"uploadID"];
if (uploadID.integerValue == uploadActivity.uploadID)
{
[self setUploadComplete];
[[ApplicationActivities getSharedActivities] markUploadAsFinished:uploadActivity];
NSLog(#"BEGINNING RELOAD");
[parentTable reloadData];
NSLog(#"ENDING RELOAD");
}
}
Now the problem is when they call their owning tableview. When the view which the tableview is contained within dismisses, the old custom cell objects are still alive in the background getting NSNotfications. And when that upload is then done, the old custom cell objects from the former table views still tries to call that parentTable property which was set at that time, now resulting in calling random junk memory.
The way I solved this was to keep an array of all cell objects getting created in the table and then make them stop listening when the view is dismissed like this:
-(void) viewWillDisappear:(BOOL)animated
{
for (UploadCell *aCell in lol)
{
[aCell stopListening];
}
[self.navigationController popViewControllerAnimated:YES];
}
But this seems like a bit of a hack. How would I go about making sure that the custom cell objects are deleted when the view is dismissed? Because when the view is intialized again, new cells are simply made anyways, so I have no use for the old ones.
The custom view cells have a strong property pointer to the tableview they get associated with, but I thought the ARC would make sure that TableView pointer would not get invalidated then? Obviously it is somehow. Maybe because of the containing view being deleted when popped?
Sounds like the cells have a retain property pointing back to your UITableViewDataSource class.
They should instead have an assign property, then they will be released properly when the table view is released (which it currently cannot be if your cells are retaining it).
Also, the cells should shut down notifications when they are dropped out of the tableview, by overriding the cells didMoveToSuperview method:
- (void)didMoveToSuperview
{
[super didMoveToSuperview];
if ( [self superview] == nil )
{
[self unsubscribeFromYourNotifications];
}
}
That is so if they scroll off screen they will not be wasting resources updating things.
Have you considered a separate update model that keeps a map between uploadIDs and cells that listens for the notification? That way, the cells aren't responsible for updating the table themselves, the update model would do it. When the table goes away, you can shut down the update model.

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