Transformable attributes are useful for storing nonstandard object types within Core Data.  For example, I provide code in [this answer][1] that lets you store UIImages as an attribute within Core Data.  The image data is converted to and from an NSData instance that contains the image&#39;s PNG representation.  This is all handled transparently for you by a custom NSValueTransformer.

You may also wish to encrypt individual attributes within your Core Data model, as I [describe here][2].  Using a transformable attribute for this makes this trivial to code.


  [1]: https://stackoverflow.com/questions/1598600/why-is-my-transformable-core-data-attribute-not-using-my-custom-nsvaluetransforme/1601546#1601546
  [2]: https://stackoverflow.com/questions/1645007/how-can-i-encrypt-coredata-contents-on-an-iphone/1646605#1646605

I&#39;m trying to long-term serialize a bunch of objects related by a strong class hierarchy in java, and I&#39;d like to use protocol buffers to do it due to their simplicity, performance, and ease of upgrade.  However, they don&#39;t provide much support for polymorphism.  Right now, the way I&#39;m handling it is by having a &quot;one message to rule them all&quot; solution that has a required string uri field that allows me to instantiate the correct type via reflection, then a bunch of optional fields for all the other possible classes I could serialize, only one of which will be used (based on the value of the uri field).  Is there a better way to handle polymorphism, or is this as good as I&#39;m going to get?

what&#39;s the right way to do polymorphism with protocol buffers?

I&#39;m wondering is there any difference in performance of using CSS Transitions vs. any of the various JavaScript animation libraries? (`script.aculo.us`, `scripty2`, `jsAnim`, `MooTools`, `$fx`, etc).

I&#39;ve tried various tests in *Safari* and *Chrome* but I don&#39;t actually see any difference. I thought that CSS Transitions were supposed to be hardware accelerated.

--- 
**Update**:

I&#39;ve tried using Scriptaculous&#39; `Effect.Fade` on 5 different DIVs (each containing a canvas with some lines). Doing the exact same thing using CSS transitions, I see absolutely no difference in performance. Both were very smooth with one DIV/Canvas, but both are very slow when I do more than 2 at a time.

I&#39;ve tried this in *Safari 4, 5 (OSX)*, *Google Chrome 5* and *FireFox 3.7pre*. Same results across the board.

In answer to UpHelix&#39;s response, you&#39;re not simply limited to `hover`, etc. You can trigger a transition by changing any `transitionable` style. For instance, set the opacity of an element in JavaScript (after, you&#39;ve specified the `transitionPropery` and `transitionDuration` for that element).

Performance of CSS Transitions vs. JS animation packages

There&#39;s this Transformable data type for attributes. What is it good for? Are there good examples?

I&#39;d like to play around with this. So after searching a while I came across this: NSValueTransformer. Seems to be something I need for this.

So how would I get started with this? For example, if I wanted to store an UIColor object, would I make an transformer for that?

What exactly is this thing transforming to or from? An NSData? And must the object which I pass to the transformer follow any protocol?

What can I do with an Transformable attribute type in Core Data on the iPhone?

There's this Transformable data type for attributes. What is it good for? Are there good examples?
I'd like to play around with this. So after searching a while I came across this: NSValueTransformer. Seems to be something I need for this.
So how would I get started with this? For example, if I wanted to store an UIColor object, would I make an transformer for that?
What exactly is this thing transforming to or from? An NSData? And must the object which I pass to the transformer follow any protocol?

On my iphone app, I have a UITableView in edit mode, where user is allowed only to reorder the rows no delete permission is given. 

So is there any way where I can hide &quot;-&quot; red button from TableView. Please let me know. 

Thanks




Is there any way to hide &quot;-&quot; (Delete) button while editing UITableView

How can I add a background image to a UILabel in an iPhone Application. I&#39;ve tried to do it through IB but with no result.

Adding Background image to UILabel

Let&#39;s say we have a view controller with one sub view. the subview takes up the center of the screen with 100 px margins on all sides. We then add a bunch of little stuff to click on inside that subview. We are only using the subview to take advantage of the new frame ( x=0, y=0 inside the subview is actually 100,100 in the parent view). 

Then, imagine that we have something behind the subview, like a menu. I want the user to be able to select any of the &quot;little stuff&quot; in the subview, but if there is nothing there, I want touches to pass through it (since the background is clear anyway) to the buttons behind it. 

How can I do this? It looks like touchesBegan goes through, but buttons don&#39;t work. 

How can I click a button behind a transparent UIView?

I have added a `UISegmentedControl` in my application.  None of the buttons are selected in normal state.  I want to implement a button click event when the first segment is selected, and another event when another button is clicked.

Define click event for UISegmentedControl

I&#39;m trying to create a universal iPhone app, but it uses a class defined only in a newer version of the SDK. The framework exists on older systems, but a class defined in the framework doesn&#39;t.

I know I want to use some kind of weak linking, but any documentation I can find talks about runtime checks for function existence - how do I check that a class exists?

Weak Linking - check if a class exists and use that class

Hey, I&#39;m working on the model layer for our app here.

Some of the requirements are like this:

 1. It should work on iPhone OS 3.0+.
 2. The source of our data is a RESTful Rails application.
 3. We should cache the data locally using Core Data.
 4. The client code (our UI controllers) should have as little knowledge about any network stuff as possible and should query/update the model with the Core Data API.

I&#39;ve checked out the *WWDC10 Session 117* on Building a Server-driven User Experience, spent some time checking out the [Objective Resource](https://github.com/yfactorial/objectiveresource/tree/master), [Core Resource](http://coreresource.org), and [RestfulCoreData](http://github.com/lukeredpath/RestfulCoreData) frameworks. 

The Objective Resource framework doesn&#39;t talk to Core Data on its own and is merely a REST client implementation. The Core Resource and RestfulCoreData all assume you talk to Core Data in your code and they solve all the nuts and bolts in the background on the model layer.

All looks okay so far and initially I though either Core Resource or RestfulCoreData will cover all of the above requirements, but... There&#39;s a couple of things none of them seemingly happen to solve correctly:

1. The main thread should not be blocked while saving local updates to the server.
2. If the saving operation fails the error should be propagated to the UI and no changes should be saved to the local Core Data storage.

Core Resource happens to issue all of its requests to the server when you call `- (BOOL)save:(NSError **)error` on your Managed Object Context and therefore is able to provide a correct NSError instance of the underlying requests to the server fail somehow. But it blocks the calling thread until the save operation finishes. FAIL.

RestfulCoreData keeps your `-save:` calls intact and doesn&#39;t introduce any additional waiting time for the client thread. It merely watches out for the `NSManagedObjectContextDidSaveNotification` and then issues the corresponding requests to the server in the notification handler. But this way the `-save:` call always completes successfully (well, given Core Data is okay with the saved changes) and the client code that actually called it has no way to know the save might have failed to propagate to the server because of some `404` or `421` or whatever server-side error occurred. And even more, the local storage becomes to have the data updated, but the server never knows about the changes. FAIL.

So, I&#39;m looking for a possible solution / common practices in dealing with all these problems:

1. I don&#39;t want the calling thread to block on each `-save:` call while the network requests happen.
2. I want to somehow get notifications in the UI that some sync operation went wrong.
3. I want the actual Core Data save fail as well if the server requests fail.

Any ideas?




How to sync CoreData and a REST web service asynchronously and the same time properly propagate any REST errors into the UI

I need to create `NSManagedObject` instances, do some stuff with them and then trash them or store to sqlite db. The problem is, I cannot create instances of `NSManagedObject` unconnected to `NSManagedObjectContext` and this means I have to clear up somehow  after I decide that I don&#39;t need some of the objects in my db. 

To deal with it, I have created an in-memory store using the same coordinator and I&#39;m placing temporary objects there by using `assignObject:toPersistentStore.` Now, how do I ensure that these temporary objects don&#39;t get to the data, which I fetch from the common to both stores context? Or do I have to create separate contexts for such a task?


----------


UPD:
----

Now I&#39;m thinking about making separate context for in-memory store. How do I move objects from one context to another? Just using [context insertObject:]? Will it work OK in this setup? If I insert one object from the graph of objects, does the whole graph also get inserted into context?

How to Deal with Temporary NSManagedObject instances?

There is a [previous SO post][1] regarding setting up error domains for your own frameworks, but what is the best practice regarding setting up error domains and custom error codes *for your own project/app*?

For example, supposing you&#39;re working on a Core Data-intensive app with lots of validations, should you just stick with the &quot;off the shelf&quot; Core Data error codes (such as `NSManagedObjectValidationError` from `CoreDataErrors.h`) or should you create your own `MyAppErrors.h` and define errors with more specificity (i.e., `MyAppValidationErrorInvalidCombinationOfLimbs`?

Creating a custom error domain and set of error codes could significantly disambiguate your code, but is it too much overhead to maintain and does one have to worry about error code numbering conflicts?  Or are there other concerns here?

  [1]: https://stackoverflow.com/questions/1779034/nserror-domains-custom-domains-conventions-and-best-practices

Best Practice - NSError domains and codes for your own project/app

I&#39;m stuck on a problem for hours now and having read everything about this on stackoverflow (and apply every advices found), I&#39;m now officially in need for help. ;o)

Here is the context :

In my iPhone project, I need to import data on the background and insert it in a managed object context. Following the advices found here, here is what I&#39;m doing :

- Save the main moc
- Instantiate a background moc with the persistent store coordinator used by the main moc
- Register my controller as an observer of the NSManagedObjectContextDidSaveNotification notification for the background moc
- Call the import method on a background thread
- Each time data is received, insert it on the background moc
- Once all the data has been imported, save the background moc
- Merge the changes into the main moc, on the main thread
- Unregister my controller as an observer for the notification
- Reset and release the background moc

Sometimes (and randomly), the exception...

    *** Terminating app due to uncaught exception &#39;NSGenericException&#39;, reason: &#39;*** Collection &lt;__NSCFSet: 0x5e0b930&gt; was mutated while being enumerated...

...is thrown when I call executeFetchRequest on the background moc, to check if the imported data already exists in the database. I wonder what is mutating the set since there is nothing that run outside the import method.

I&#39;ve included the entire code of my controller and my test entity (my project consisting of these two classes and the app delegate, which has been unmodified) :


    //
    //  RootViewController.h
    //  FK1
    //
    //  Created by Eric on 09/08/10.
    //  Copyright (c) 2010 __MyCompanyName__. All rights reserved.
    //
    
    
    #import &lt;CoreData/CoreData.h&gt;
    
    @interface RootViewController : UITableViewController &lt;NSFetchedResultsControllerDelegate&gt; {
        NSManagedObjectContext *managedObjectContext;
    	NSManagedObjectContext *backgroundMOC;
    }
    
    
    @property (nonatomic, retain) NSManagedObjectContext *managedObjectContext;
    @property (nonatomic, retain) NSManagedObjectContext *backgroundMOC;
    
    @end


    //
    //  RootViewController.m
    //  FK1
    //
    //  Created by Eric on 09/08/10.
    //  Copyright (c) 2010 __MyCompanyName__. All rights reserved.
    //
    
    
    #import &quot;RootViewController.h&quot;
    #import &quot;FK1Message.h&quot;
    
    @implementation RootViewController
    
    @synthesize managedObjectContext;
    @synthesize backgroundMOC;
    
    - (void)viewDidLoad {
        [super viewDidLoad];
    	
    	self.navigationController.toolbarHidden = NO;
    	
    	UIBarButtonItem *refreshButton = [[UIBarButtonItem alloc] initWithBarButtonSystemItem:UIBarButtonSystemItemRefresh target:self action:@selector(refreshAction:)];
    	
    	self.toolbarItems = [NSArray arrayWithObject:refreshButton];
    }
    
    #pragma mark -
    #pragma mark ACTIONS
    
    - (void)refreshAction:(id)sender {
    	// If there already is an import running, we do nothing
    	
    	if (self.backgroundMOC != nil) {
    		return;
    	}
    
    	// We save the main moc
    	
    	NSError *error = nil;
    	
    	if (![self.managedObjectContext save:&amp;error]) {
    		NSLog(@&quot;error = %@&quot;, error);
    		
    		abort();
    	}
    	
    	// We instantiate the background moc
    	
    	self.backgroundMOC = [[[NSManagedObjectContext alloc] init] autorelease];
    	
    	[self.backgroundMOC setPersistentStoreCoordinator:[self.managedObjectContext persistentStoreCoordinator]];
    		
    	// We call the fetch method in the background thread
    	
    	[self performSelectorInBackground:@selector(_importData) withObject:nil];
    }
    
    - (void)_importData {
    	NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];
    	
    	[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(backgroundMOCDidSave:) name:NSManagedObjectContextDidSaveNotification object:self.backgroundMOC];			
    	
    	FK1Message *message = nil;
    	
    	NSFetchRequest *fetchRequest = nil;
    	NSEntityDescription *entity = [NSEntityDescription entityForName:@&quot;FK1Message&quot; inManagedObjectContext:self.backgroundMOC];
    	NSPredicate *predicate = nil;
    	NSArray *results = nil;
    	
        // fake import to keep this sample simple

    	for (NSInteger index = 0; index &lt; 20; index++) {
    		predicate = [NSPredicate predicateWithFormat:@&quot;msgId == %@&quot;, [NSString stringWithFormat:@&quot;%d&quot;, index]];
    		
    		fetchRequest = [[[NSFetchRequest alloc] init] autorelease];
    		
    		[fetchRequest setEntity:entity];
    		[fetchRequest setPredicate:predicate];
    		
    		// The following line sometimes randomly throw the exception :
    		// *** Terminating app due to uncaught exception &#39;NSGenericException&#39;, reason: &#39;*** Collection &lt;__NSCFSet: 0x5b71a00&gt; was mutated while being enumerated.
    		
    		results = [self.backgroundMOC executeFetchRequest:fetchRequest error:NULL];
    				
    		// If the message already exist, we retrieve it from the database
    		// If it doesn&#39;t, we insert a new message in the database
    		
    		if ([results count] &gt; 0) {
    			message = [results objectAtIndex:0];
    		}
    		else {
    			message = [NSEntityDescription insertNewObjectForEntityForName:@&quot;FK1Message&quot; inManagedObjectContext:self.backgroundMOC];
    			message.msgId = [NSString stringWithFormat:@&quot;%d&quot;, index];
    		}
    
    		// We update the message
    		
    		message.updateDate = [NSDate date];
    	}
    
    	// We save the background moc which trigger the backgroundMOCDidSave: method
    	
    	[self.backgroundMOC save:NULL];
    	
    	[[NSNotificationCenter defaultCenter] removeObserver:self name:NSManagedObjectContextDidSaveNotification object:self.backgroundMOC];
    	
    	[self.backgroundMOC reset]; self.backgroundMOC = nil;
    	
    	[pool drain];
    }
    
    - (void)backgroundMOCDidSave:(NSNotification*)notification {	
    	if (![NSThread isMainThread]) {
    		[self performSelectorOnMainThread:@selector(backgroundMOCDidSave:) withObject:notification waitUntilDone:YES];
    		return;
    	}
    	
    	// We merge the background moc changes in the main moc
    	
    	[self.managedObjectContext mergeChangesFromContextDidSaveNotification:notification];
    }
    
    @end

    //
    //  FK1Message.h
    //  FK1
    //
    //  Created by Eric on 09/08/10.
    //  Copyright 2010 __MyCompanyName__. All rights reserved.
    //
    
    #import &lt;CoreData/CoreData.h&gt;
    
    @interface FK1Message :  NSManagedObject  
    {
    }
    
    @property (nonatomic, retain) NSString * msgId;
    @property (nonatomic, retain) NSDate * updateDate;

    @end

    // 
    //  FK1Message.m
    //  FK1
    //
    //  Created by Eric on 09/08/10.
    //  Copyright 2010 __MyCompanyName__. All rights reserved.
    //
    
    #import &quot;FK1Message.h&quot;
    
    @implementation FK1Message 
    
    #pragma mark -
    #pragma mark PROPERTIES
    
    @dynamic msgId;
    @dynamic updateDate;
    
    @end

This is all ! The whole project is here. No table view, no NSFetchedResultsController, nothing else than a background thread that import data on a background moc.

What could mutate the set in this case ?

I&#39;m pretty sure I&#39;m missing something obvious and it&#39;s driving me mad.

EDIT: 

Here is the full stack trace :

        2010-08-10 10:29:11.258 FK1[51419:1b6b] *** Terminating app due to uncaught exception &#39;NSGenericException&#39;, reason: &#39;*** Collection &lt;__NSCFSet: 0x5d075b0&gt; was mutated while being enumerated.&lt;CFBasicHash 0x5d075b0 [0x25c6380]&gt;{type = mutable set, count = 0,
    entries =&gt;
    }
    &#39;
    *** Call stack at first throw:
    (
    	0   CoreFoundation                      0x0255d919 __exceptionPreprocess + 185
    	1   libobjc.A.dylib                     0x026ab5de objc_exception_throw + 47
    	2   CoreFoundation                      0x0255d3d9 __NSFastEnumerationMutationHandler + 377
    	3   CoreData                            0x02287702 -[NSManagedObjectContext executeFetchRequest:error:] + 4706
    	4   FK1                                 0x00002b1b -[RootViewController _fetchData] + 593
    	5   Foundation                          0x01d662a8 -[NSThread main] + 81
    	6   Foundation                          0x01d66234 __NSThread__main__ + 1387
    	7   libSystem.B.dylib                   0x9587681d _pthread_start + 345
    	8   libSystem.B.dylib                   0x958766a2 thread_start + 34
    )
    terminate called after throwing an instance of &#39;NSException&#39;



&quot;Collection was mutated while being enumerated&quot; on executeFetchRequest

I have a user interface to insert a Transaction. once the user clicks on a plus he gets the screen and i want to instantiate my Core Data NSManagedObject entity let the user work on it. Then when the user clicks on the Save button i will call the save function.

so down to code:

    transaction = (Transaction *)[NSEntityDescription insertNewObjectForEntityForName:@&quot;Transaction&quot; inManagedObjectContext:self.managedObjectContext];
    //even if i dont call save: its going to show up on my table
    [self.managedObjectContext save:&amp;error]


P.S i am using an NSFetchedResultsController on that table and I see that the NSFetchedResultsController is inserting a section and an object to the table.

My thought is if there is a way to instantiate the Transaction NSManagedObject i could update it with out saving untill the client choses to.

Content Type	Original Author	Original Content on Stackoverflow
Question	dontWatchMyProfile	View Question on Stackoverflow
Solution 1 - Ios	Brad Larson	View Answer on Stackoverflow

What can I do with an Transformable attribute type in Core Data on the iPhone?

Ios Problem Overview

Ios Solutions

Solution 1 - Ios

Performance of CSS Transitions vs. JS animation packages

what's the right way to do polymorphism with protocol buffers?

Attributions