My app involves a main screen with several sorting/viewing options of a set of data. Depending on what the user chooses, I may list them, e.g. alphabetically, N most recent, or grouped somehow.
I started the app as a Core Data Table-based navigation app; my app delegate sets up the Core Data stack (unchanged generated code), gives the NSManagedObjectContext to the controller for the initial screen, and it passes it to the UITableViewController implementing my "list of entities".
Since my three different views of the same data all end up showing a table listing out the data, I expanded this class to have three different NSFetchedResultsControllers, each with the one UITableViewController instance as their delegate. Before pushing this view controller on the stack, I call a method to switch which NSFetchedResultsController to use, e.g.
-(void)configureForMostRecent {
self.activeFetchedResultsController = self.mostRecentResultsController;
}
Now I am getting random crashes from Core Data, e.g. NSInternalInconsistencyException and other things like that. Sometimes, I use the app and everything's fine, other times, it crashes almost instantly.
So, my instinct is that my design is just a Bad Idea(tm).
Should I basically stick to a "One UITableViewController to one NSFetchedResultsController" sort of model and just use other coding styles to reduce boilerplate?
Using multiple NSFetchedResultsController instances is a perfectly valid design based on the description you have given so far.
Are you trying to use the same cache for each of these NSFetchedResultsController instances? Are you calling -reloadData on the table whenever you switch to a different NSFetchedResultsController? Both of those could be causing the crash you are seeing.
Update
The delegate is not an issue but not calling -reloadData is going to be a killer. The delegate methods really are there just to update the UITableView when the NSFetchedResultsController changes. The fact that a reference to is passed into those delegate methods is a hint that they are designed to handle multiple NSFetchedResultController` instances calling into them.
You could use one fetch controller, adjusting the fetch predicate and refetching as needed.
EDIT
Following my example case:
[NSFetchedResultsController deleteCacheWithName:#"MyObjectsCache"];
NSPredicate *_predicate = nil;
if (condition) {
_predicate = [NSPredicate predicateWithFormat:mySearchPredicateString];
self.currentTableView = searchDisplayController.searchResultsTableView;
}
else {
_predicate = [NSPredicate predicateWithFormat:myDefaultPredicateString];
self.currentTableView = tableView;
}
[fetchedResultsController.fetchRequest setPredicate:_predicate];
NSError *_error = nil;
if (![fetchedResultsController performFetch:&_error]) {
// handle error
}
Related
I'm trying to pass int variable to UITableView through UINavigationController (I'm using xcode 4.3) So I created 2 classes (PartsTableViewController that is "UITableViewController" and PartsNavController that is "UINavigationController"), I want to pass the variable from my current class to PartsTableViewController and then open that table with its Navigation controller that contains the title bar , so I wrote in my current class the following code:
PartsNavController *partsNav = [self.storyboard instantiateViewControllerWithIdentifier:#"partsNav"];
partsNav.groupId = myGroupp.bg_id;
[self presentModalViewController:partsNav animated:YES];
and in the PartsNavController class I wrote in viewDidLoad:
PartsTableViewController *parts = [self.storyboard instantiateViewControllerWithIdentifier:#"Parts"];
parts.groupId = groupId;
[parts.tableView reloadData];
and in PartsTableViewController I wrote in viewDidLoad:
NSLog(#"This is group: %d", groupId);
but when run, it generates the output 2 times,
This is group:1
This is group:0
first time is the value that I sent and the second time it outs 0 , I just want the value that I sent, not 0
how can I prevent this and get just the value that I sent ????
I want to pass from (MaktabatyTableViewController) to (PartsTableViewController) without using segue
The better way to do what you want is to push second TableViewController in existing UINavigationController. The easiest way to do that is to create that NavContr in StoryBoard and than to TableViews and connect it's cell with leading view controller with segue. And than use method below:
-(void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender {
UIViewController *destViewController = segue.destinationViewController;
destViewController.integerValue = value;
}
I want to pass from (MaktabatyTableViewController) to
(PartsTableViewController) without using segue
There are (at least) two strategies you can choose from:
Direct communication: People often ask how to communicate between two objects, and it almost always boils down one of the objects having a reference to the other (and sometimes vice versa). To send a message to an object, you need a pointer to that object; if you've got the pointer, there's no mystery about how to communicate. Thinking about it in those terms helps you think about the issue a little differently: instead of the immediate "how do I send a message to that object?" you can instead focus on the relationship between the two objects. How was each one created? Is one of the objects the parent of the other? Is there some common parent object that can provide a pointer? How should the objects be related, if at all?
Indirect communication: Sometimes instead of having two objects communicate directly, it's more appropriate to route the communication through some intermediate object. For example, your MaktabatyTableViewController might send a message to its delegate, and the delegate could then pass the information on to PartsTableViewController. A much more general solution is to use notifications: MaktabatyTableViewController could post a notification that PartsTableViewController listens for. The intermediate object in this case is the notification center. Either way, the advantage that you get with indirect communication is that neither object has to know about the other. That reduces coupling between the two classes and makes them both more flexible and more reusable.
From what I can see in your question, I'd suggest using notifications.
I'm using core data and NSFetchedResultsController in an app, for feeding a UIViewTable with Car objects. I have a button that, when tabbed, takes the app to another view when the user can add a new Car. The problem I have is that even if the user doesn't create the car in the second view, it's added to the table. If I restart the application, the Car wasn't added to the DB.
This is related to the fact that I create an instance of the Car in the second view, in the viewDidLoad method, using something like this:
car = [NSEntityDescription insertNewObjectForEntityForName:#"Car"
inManagedObjectContext:context];
This is added even if I don't save the context.
I tried to delete the object when the second view is about to be closed, using this:
[context deleteObject:car];
This partially works. The car is not added to the table in the first page, but looks like the indexes of the data source are altered. If I scroll all the way down I got this error:
*** Terminating app due to uncaught exception 'NSRangeException', reason: '*** -[_PFBatchFaultingArray objectAtIndex:]: index (9) beyond bounds (9)'
Any ideas will be appreciated.
Try creating your car object by passing a nil context:
car = [NSEntityDescription insertNewObjectForEntityForName:#"Car"
inManagedObjectContext:nil];
From there, if the user decides to save it you can move the object to the main context.
The other alternative is to have a separate MOC for this view (which adds unnecessary complications) and then again move the object between contexts if/when required.
Cheers,
Rog
PS: if you're wondering whether you can pass nil as the managedObjectContext, this is straight from Apple's docs on NSManagedObject:
...If context is not nil, this method
invokes [context insertObject:self]
(which causes awakeFromInsert to be
invoked)...
More details here
[EDIT]
In addition to this, I just came across something interesting when looking at the NSFetchRequest documentation and thought you might want to have a go (I haven't tried myself). It appear that you can tell the fetchRequest whether to include pending changes (i.e. not saved) or not when fetching objects:
- (void)setIncludesPendingChanges:(BOOL)yesNo
FYI the default value is YES - more details here
First, try delaying the insertion of the new object when the user commits the change.
Only if it's not appropriate:
When the context has changed, NSFetchedResultsController is automatically informed to modify its data passed to the table view controller. However, the table view itself is not modified, so you have to update the table view by yourself.
That's why NSFetchedResultsController has a delegate object (conforming to NSFetchedResultsControllerDelegate protocol) which is responsible to update the table view.
For example, in CoreDataBooks sample project, you will see delegate methods of this protocol in RootViewController class. The most related delegate method is controller: didChangeObject: atIndexPath: forChangeType: newIndexPath:. You may probably want to do something like the following:
if (changeType == NSFetchedResultsChangeDelete) {
[tableView deleteRowsAtIndexPaths:[NSArray arrayWithObject:indexPath] withRowAnimation:UITableViewRowAnimationFade];
}
I apologise if this has been asked before but I can't find the info I need.
Basically I want a UITableView to be populated using info from a server, similar to the SeismicXML example. I have the parser as a separate object, is it correct to alloc, init an instance of that parser & then tell RootViewController to make it's table data source a copy of the parser's array.
I can't include code because I haven't written anything yet, I'm just trying to get the design right before I start. Perhaps something like:
xmlParser = [[XMLParser alloc] init];
[xmlParser getXMLData];
// Assuming xmlParser stores results in an array called returnedArray
self.tableDataSource = xmlParser.returnedArray
Is this the best way of doing it?
No, you don't want to do this. You don't want your view controller directly accessing the array of the data-model. This would work in the technical sense but it would be fragile and likely to fail as the project scaled.
As the projects grow in complexity, you will want to increasingly wrap your data model object (in this case the xmlParser) in protective layers of methods to control and verify how the data model changes. Eventually, you will have projects with multiple views, multiple view controllers as well as information entering from both the user and URLs. You need to get into the habit of using the data-model object not just a dumb store you dump stuff into but as an active manager and verifier of your data.
In a situation like this I would have my data-model's array completely wrapped by making it a #protected or #private property. Then I would have dedicated methods for fetching or inserting data into the actual array inside the data-model class itself. No objects outside of the data-model should actually have direct access to the array or have knowledge of its indexes.
So, in this case your data-model would have something like:
- (NSString *) textForLineAtIndexPath:(NSIndexPath *) anIndexPath{
//... do bounds checking for the index
NSString *returnString=[self.privateArray objectAtIndex:anIndexPath.row];
if (returnString=='sometest'){
return returnString;
}
return #""; //return an empty string so the reciever won't nil out and crash
}
as well as a setTextForLineAtPath: method for setting the line if you need that.
The general instructional materials do not spend enough (usually none) time talking about the data-model but the data-model is actually the core of the program. It is where the actual logic of the application resides and therefore it should be one of the most complex and thoroughly tested class in your project.
A good data-model should be interface agnostic i.e. it should work with a view based interface, a web based interface or even the command line. It should neither know nor care that its data will be displayed in a tableview or any other interface element or type.
When I start a new project, the first thing I do is comment out the '[window makeKeyAndVisible];' in the app delegate. Then I create my data-model class and test it old-school by loading data and logging the outputs. Only when it works exactly how I wish it to do I then proceed to the user interface.
So, think real hard about what you want the app to do on an abstract level. Encode that logic in a custom class. Isolate the data from all direct manipulation from any other object. Verify all inputs to the data before committing.
It sounds like a lot of work and it is. It feels like overkill for a small project and in many cases it is. However, getting the habit early will pay big dividends very quickly as your apps grow in complexity.
Not quite. You want the data source to be an object that implements the UITableViewDataSource protocol; what I would do in this situation is create an object that implements that protocol and parses XML, so that you can alloc-init it, then set the data source to that object and have it update the table view as appropriate. So based off your code (and assuming you're running within the table view's controller):
XMLParserAndDataSource xpads = [[XMLParserAndDataSource alloc] init];
[xpads getXMLData];
self.tableView.dataSource = xpads;
It's probably a good idea to give this class itself a reference to an NSXMLParser object, so you can use that to parse the XML, then provide convenience methods (like getXMLData) as well as the UITableViewDataSource methods for your own use. (If you go this route, you should also make your XMLParserAndDataSource class implement the more useful of the NSXMLParser delegate methods, and use them as appropriate to update your table view.)
I'm a Mac programmer and not an iPhone programmer; but on the mac,
self.tableDataSource = xmlParser.returnedArray is not correct. You are supposed to either bind the table's content to an Array Controller (if iPhone has one?) or set the datasource outlet to your RootViewController.
In your rootview controller, you would implement the methods:
– tableView:cellForRowAtIndexPath:
– tableView:numberOfRowsInSection:
For – tableView:cellForRowAtIndexPath: you would return a UITableViewCell with the data you received from the XML parsing according to the index path like so:
UITableCell *myCell = [UITableCell new];
myCell.textLabel.text = [parsedXMLArray objectAtIndex:[indexPath indexAtPosition:indexPath.length-1]];
return myCell;
(Something people don't know is that you can use the + new class method on all NSObject subclasses which automatically call alloc/init.)
For – tableView:numberOfRowsInSection just return the count of the data array:
return parsedXMLArray.count;
Can't edit my question nor post replies, can only post my response as answer.
#TechZen: I'm somebody who tries to form analogies, helps me understand. What you're saying is something like: My original idea was like going into the file room & dumping all the originals on my desk to work on where as you suggest the object be more like an organised file clerk who will search through the data for me and only return the specific datum that I need while being the only one with direct access to that data.
Have I understood correctly?
#Tim: What if I later need the parser to get data for something which is not a table? That's why I thought to dump it into an array & let the caller decide what to do with the data. Would you suggest a second object that would supply the data in the newly required form? (Am I sort of one the right track here or way off?)
Maybe a FAQ at this website.
I have a TableViewController that holds a form. In that form I have two fields (each in it's own cell): one to select who paid (single selection), and another to select people expense is paid for (multiple selection).
Both fields open a new TableViewController included in an UINavigationController.
Single select field (Paid By) holds an object Membership
Multiple select field (Paid For) holds an object NSMutableArray
Both vars are being sent to the new controller identically the same way:
mySingleSelectController.crSelectedMember = self.crPaidByMember;
myMultipleSelectController.crSelectedMembers = self.crSelectedMembers;
From Paid for controller I use didSelectAtIndexPath method to set a mutable array of Memberships for whom is paid:
if ([[tableView cellForRowAtIndexPath:indexPath] accessoryType] == UITableViewCellAccessoryCheckmark) {
[self.crSelectedMembers removeObject:[self.crGroupMembers objectAtIndex:indexPath.row]];
//...
}
else {
[self.crSelectedMembers addObject:[self.crGroupMembers objectAtIndex:indexPath.row]];
//...
}
So far everything goes well. An mutable array (crSelectedMembers) is perfectly set from child view.
But...
I have trouble setting Membership object.
From Paid By controller I use didSelectAtIndexPath to set Membership:
[self setCrSelectedMember:[crGroupMembers objectAtIndex:indexPath.row]];
By NSlogging crSelectedMember I get the right selected member in self, but in parent view, to which ivar is pointed, nothing is changed.
Am I doing something wrong? Cause I CAN call the method of crSelectedMembers, but I can't change the value of crSelectedMember.
If I understand your question, the most likely cause is an improper property declaration.
If you want to pass values from one object to another using each objects properties, then you need to make sure to use assign to ensure the properties in one object are pointing at the same instances as the property in the other object.
So in your topViewController you have a property:
#property (nonatomic,retain) NSString crSelectedMember;
Then in your child view controllers you have:
#property (nonatomic,assign) NSString crSelectedMember;
This forces the value into the exact object in the parent controller.
However, this is a very fragile way to pass data between viewControllers. As your app becomes more complicated, it will be impossible to track all the passed data. (Worse, if you run into memory limitations, the parent view controller may unload and not even exist when you try to pass data to it.)
Instead, you should have a single custom object devoted to holding your data. Each view controller should query that object for the data it needs and should write any changes back to that object. The view controllers never communicate directly. This technique allows you to control the data in one specific location instead of spreading it out all over your code and it scales well. You can add an arbitrary number of view controllers to you app without having to worry about tying them all together.
See this post for details: iPhone: How to Pass Data Between Several Viewcontrollers in a Tabbar App
This seems to be a common problem, but I can't figure out anything from the answers I've seen so far. I have an iPhone app that uses a subclass of NSMutableArray to store objects, plus some additional properties. The subclass is skhCustomArray. The subclass initializes fine, with no objects in the skhCustomArray, and I assign it to the the property of my view controller, which is a pointer to an skhCustomArray.
prescriptionListVC* newPrescList = [[prescriptionListVC alloc] initWithNibName:#"PrescriptionList" bundle:nil];
newPrescList.curPersonPrescriptions = [personDetails objectAtIndex:0];
That works fine. Yet when I push my view managed by my view controller onto the navigation controller stack, the count method in the numberOfRowsInSection method crashes the app, see below.
- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section {
// Return the number of rows in the section.
return [curPersonPrescriptions count];
}
What could be causing this? How can a valid custom array, with no objects, not return a valid count? Where am I going wrong? Thanks.
Subclass of NSArray? You're aware that NSArray is a class cluster, and is therefore somewhat difficult to subclass, right? In fact, it's so fraught with danger that the NSArray documentation has a whole section dedicated to what you need to do in order to subclass it.
I'll bet that that's the source of your woes.
You almost certainly don't need to subclass NSMutableArray in this situation. Instead, make a new class which has an array as a property, along with the extra properties you desire.
When you subclass NSMutableArray, you need to implement some mandatory methods like count, addObject:, insertObjectAtIndex etc. This is what we call as class cluster.
If you want to add some more feature/behavior to already implemented object then you can write a "category" instead of "subclassing" it.
If you want to subclass it, then you have to implement all those methods which your are going to use so better write a category of NSMutableArray and extend the feature what you want and use the NSMutableArray object only. This will solve your problem and also this is the easy and almost right way to add new behavior to already existing class.