I have some NSManagedObject subclass in my app, and I'm trying to understand when and how to save changes.
I will try to explain myself, for example class A is NSManagedObject subclass.
During app life cycle I do:
App launched
...
Create an instance of class A
...
Change some properties of A instance
...
App go to background
...
App becomes active again
...
Change some more properties of A instance
...
App terminates
When do I need to call [context save:] ??
Do I call it after every change in A instance? Or maybe I call it only when app go to background?
Should I call it after creation or deletion of any A instance?
A nice approach is place UIManagedDocument in your AppDelegate. Then you can call [context save] whenever some change occurs in the app (like a crash). The order I like to follow is something like:
Create UIManagedDocument object (in application did load or wherever)
and assign it to a property
Setup the document (check whether it exist on disk or is already open, etc.. and respond accordingly)
Pass the UIManagedObjectContext to the initial UIViewController in your app (from there you can pass the context to other view controllers)
UIManaged document will save the context for you.
Take a look at the UIManagedDocument documentation to configure persistent store options (you send an NSDictionary of options to your UIManagedDocument instance, see the first example through the link below).
UIManagedDocument documentation:
http://developer.apple.com/library/ios/#documentation/UIKit/Reference/UIManagedDocument_Class/Reference/Reference.html
Also see the CoreData lecture and demo (lectures 13 and 14) of the iPhone and iPad application development course with Paul Hegarty available free on iTunesU (Fall 2011).
The data will not be saved to the persistent store until you call save. So, it depends on what you want in your app. If you want it to be able to recover the last value it ever had, then you should save after each modification.
Easy change is to just save after making modifications.
You could do something a bit more fancy, like only save after some set amount of time, so many changes are grouped together... and catch any event that will put your app in the background and then save...
But, that's what UIManagedDocument does automatically for you, so you could just use that instead.
Depending on the amount of changes that you make and the volume of data that needs to be saved with each change, yo can choose to save a little or a lot. If you are just saving a string or a number or a bool, then go ahead and call save: on your context as soon as the changes were made.
If it is a lot of data, you may want to coalasce your changes and then save it on a background queue so that you are not blocking the main queue. This way you are not waiting to go to the background to perform your saves.
Tim
Related
My application has deep navigational chains of 8+ screens deep (Wizard-style). When i'm editing a View Controller, and i want to make a quick visual change and re-test, As a tester, I have to go through the full flow to end up where I was before recompiling, in the same Data state. Is there a way that Xcode can somehow preserve the application state, and re-run the same view controller?
If there was an automated way to detect the last launched screen, and re-display it after the recompile, that would save a lot of developers a lot of time.
I realize something like this can be built custom. Something like:
IF A Certain Debug Flag is ON:
- Retrieve from NSUserDefaults the Class Name of the last controller used, and redisplay it.
The problem with this is: Data State and Navigation State will not be preserved. Also, all other object state which invokes and depends on your controller will not be included. That's why I need a more universal solution.
IF A Certain Debug Flag is ON: - Retrieve from NSUserDefaults the Class Name of the last controller used, and redisplay it.
The problem with this is: Data State and Navigation State will not be preserved.
But this is exactly the problem that the built-in state saving and restoration mechanism is intended to solve, is it not?
https://developer.apple.com/library/ios/featuredarticles/ViewControllerPGforiPhoneOS/PreservingandRestoringState.html
I recommend you use a User Interface target and then create an XCTestCase that works on your view controller and exercise it. Use the new record button in Xcode 7 to get you started with the test case. Familiarize yourself with some of the new queries it uses for some of the dynamic information you may be creating.
Another option would be to inject your test case's UI state into the application delegate in the setup function of an XCTestCase. Then it will need custom logic to navigate to the correct view controller. Then your test case could focus on just that ViewController once the Application delegate has navigated to it.
Of course you can use the debugger and breakpoints in the Test Case and your View Controller while UI Testing. By "scripting" this you do significantly less manual clicking on a device to test a ViewCOntroller
Also you've now got a Test! Hopefully worth something to you down the road when you change something
I wrote this little program which is supposed to print the current frontmost application twice, with a 3-second break in between.
void printFrontmostApp() {
NSRunningApplication *frontmostApplication = [NSWorkspace sharedWorkspace].frontmostApplication;
NSLog(#"%#",frontmostApplication);
}
int main(int argc, const char * argv[]) {
#autoreleasepool {
printFrontmostApp();
sleep(3);
printFrontmostApp();
}
return 0;
}
When I ran this program, I realised that frontmostApplication is not refreshed when it is called the second time. I found the solution here. But I still have two questions:
1) I want to know why the frontmostApplication is not updated.
2) How do I force it to refresh every time I call it? I don't want to receive a notification every time the frontmost application deactivates, because it is a little inefficient for my purposes.
Edit:
Just to be crystal clear, let's suppose the time now is 10:00:00. I call printFrontmostApp, and it prints "Xcode" to the console, because Xcode is the current frontmost app. Then the program sleeps for 3 seconds. At 10:00:01, I opened another app, say TextEdit. At 10:00:03, my program calls printFrontmostApp for the second time. I expect it to print "TextEdit", which is the current frontmost application. But it prints "Xcode" instead. I can't understand this behaviour.
Can someone please explain what happens at 10:00:03? The function seems to "remember" the value of frontmostApplication at 10:00:00 and retains it when it is called the second time. I thought that any memory will be released once it goes out of scope, so why is this happening?
And how do I get my program to get the frontmost app at 10:00:03? I can get the frontmost app at 10:00:00, I should be able to do the same 3 seconds later right?
The documentation for -[NSWorkspace runningApplications] — not the method you're using, but related — says:
Similar to the NSRunningApplication class’s properties, this property will only change when the main run loop is run in a common mode. Instead of polling, use key-value observing to be notified of changes to this array property.
From the NSRunningApplication documentation:
Properties that vary over time are inherently race-prone. For example, a hidden app may unhide itself at any time. To ameliorate this, properties persist until the next turn of the main run loop in a common mode. For example, if you repeatedly poll an unhidden app for its hidden property without allowing the run loop to run, it will continue to return NO, even if the app hides, until the next turn of the run loop.
It's a near certainty that the same principle applies to -frontmostApplication even though the documentation doesn't say so explicitly. You will never get different results by polling without allowing the run loop to run.
For 1) the answer is the same described in the question you have linked: You have to observe this notification, that tells you when a new application was activated:
NSWorkspaceDidActivateApplicationNotification
About 2) You have different observers for activation and deactivation like:
NSWorkspaceDidDeactivateApplicationNotification
So your are not going to observe notifications that you are not registered, please take a look at NSWorkspace Notifications for a comprehensive list.
Otherwise, please define your question about refreshing/polling (that I think it's not a good idea anyways).
How can I get notified when NSDocument is saved, the first time and subsequent times?
I first thought that overriding writeToURL:ofType:error: would do it, but it appears that this method is also called for temporary autosaves before the document is saved for the first time, and maybe on copy/duplicate operations.
On the other hand, setFileURL: appears to be called the first time that the document is saved but not on subsequent times.
Is there some kind of Save notification? Or do I have to work around the various border cases of the above methods?
NSDocument has writeSafelyToURL::::, which in addition to the target location URL also gets a NSSaveOperationType passed in.
This would allow you to filter out autosave operations.
Don't forget to call the super implementation when overriding writeSafelyToURL.
Long time reader, first time poster here.
I'm creating a test app that creates a NSURLConnection and then displays the result on an UILabel.
I am presently using a Notification Center observer, which fires a notification from within connectionDidFinishLoading to wait for the connection to complete successfully, before I look for the result.
However, what I am struggling to conceptualize is where to store the response data so that I can access it from my View Controller and post the result to the UILabel. (Or from anywhere other than an instance of my Connection Class, for that matter.)
I don't want to post directly to the UILabel from connectionDidFinishLoading. I need a way to decide what I will do with the response later - so my Connection Class stays generalized.
I need a better way to save the response data somewhere, where I can reference it after the instance of the Connection Class has terminated.
Ideally, it should be somewhere that I can have multiple instances of the Connection Class open, and access each response in turn as I need them. This eliminates the potential to just create a variable in my View Controller or somewhere else more global and dump the response to it.
Any ideas on what design patterns could/should be used here would be greatly appreciated!
My suggestions for you to start with are :
Make a singleton class. I will have a property NSDictionary * info or NSArray *infoList; You will have acces to the same data from wherever the app. Update the property, post the notification, access the property from the viewController.
Store the info into a plist/file. Serialize the information, or save plain stream. Whatever you like.Thus after you finish writing to the file, post the notification, read from the file from anyplace within the app.
In both cases if you want multiple connections i suggest going for the factory design Pattern.
I'm working with a document-based core-data OS X application. The problem I'm having is that whenever I edit any field on the document, after I press tab or click to something else (i.e. I finish editing/change focus), the document is marked as clean and undo is reset. When I try to save the file, however, the resulting document opens without the data I entered. What might be the problem, or, any pointers on where to look to fix this? Here's some stuff I know and things I've already tried:
I know it's not somehow saving because it never stops at the breakpoint in my overridden writeSafelyToURL:(NSURL *)inAbsoluteURL ofType:(NSString *)inTypeName forSaveOperation:(NSSaveOperationType)inSaveOperation error:(NSError **)outError and it also never sends an NSManagedObjectContextDidSaveNotification.
The documents are packaged in an NSFileWrapper directory with the core data store inside (and also some other files). I access the entities through an NSObjectController and a couple NSArrayControllers. It happens with both core data properties and manually registered changes in the rest of the file wrapper.
Update: At the suggestion of Martin, I tried NSUndoManager's notifications, and all I can seem to glean from it is that more than one undo manager is in play. If I add an observer for NSUndoManager, it won't post if I specify an object, and then if I don't, the notification object is not equal to [self undoManager]. I added updateChangeCount to my category on NSPersistentDocument, and it never gets called. setDocumentEdited basically confirmed that something about losing first responder is passing NO into that method. What could be causing this, and how can I fix it?
You could break on the method setDocumentEdited: of NSWindow to see which operation updates the change status.
In addition updateChangeCount: of NSDocument might be a place to take a look at.
NSUndoManager also posts several Notifications which can give additional hints what to look at.
The answer is actually pretty silly considering how long this stumped me. I was working on some objects on load, and I accidentally set [[self undoManager] disableUndoRegistration] at both the points where I should disable and enable. It was a little more than that, though. A related element in Interface Builder needed to be checked Prepares Content. When I had done both those things, the problem vanished.