I'm quite new to Swift, and I just started with persistence. I was wondering how the NSKeyUnarchiver works.
NSKeyedUnarchiver.unarchiveObject(withFile: file)
This is my current code. I have the file, but I don't know exactly what I'm getting. What if I archived multiple objects? How do I know which one I'm pulling? Somebody please help.
Only a single object can be archived per file. However, this can be an array, a dictionary, or other collection type, which stores multiple objects.
Related
I'm having some issues with the app, that I'm making, which I thought would be a lot easier to explain with some photos, so ... :
Ofcourse the "Create New Person-button" in nr. 1 leads you to number two.
Now, I'm having issues figuring out how to save this data about the person in the "People Diary". The goal is, that when you enter a person's name, add a photo (an enable-camera feature, I will struggle with at a later time...) and add an answer to the question - then you only need to press "Save this person", and then you will be redirected to the AllPersonsInYourDiaryViewController, where there is now a new tableViewCell with this new person's name (maybe with a subtitle containing the answer and the photo shown in miniature in the cell too).
(Naturally you can then enter this cell with the data about the person too - but that comes next.)
So far in the app, I have used NSUserDefault, when allowing the user to create this specifik Diary by the Name "Antons Diary" with the specifik question and so on. But now it came to my attention, that maybe it is smarter to use something else? I tried with dictionaries, but couldn't get this to work properly.
So...: Before I spend hours and hours playing around with one of these ways, will someone smarter than me, tell me what the best approach would be?
If I can give my two cents, the first thing you have to do is to “design” how to represent a person programmatically. You can create a struct or class to do so, even though a struct is more suitable:
struct Person {
var name: String?
var answer: String?
var photo: String?
}
Then you can decide how to save the data of such an object persistently. If you want to use a database, then I would recommend using SQLite with FMDB library. It’s really easy and fast to learn how to use it, and it's also quite handy. I've used it big projects and it works smoothly. I find CoreData too complicated and an overkill based on what you need.
If you don’t want to use a database, your only other way is to save to files, but still, you’ve got options here too. If you encode (see Codable protocol in Swift), you can use NSKeyedArchiver to convert to Data object and write then to disk. If you like using dictionaries, and since the properties you’re going to have for a person are not going to be too many, you could create a dictionary by assigning the properties and their values, and then convert and save as JSON data, or even Plist files. Without any intension to do promotion here, but just to provide some additional help, if you want take a look to a library that I’ve written and that can do all these automatically for you. It’s a protocol that you have to adopt, and then you can instantly convert your struct to a dictionary, JSON or plist and save to files.
No matter which way you’re going to select, save the images as single files to documents directory, and keep their file names only stored to database/file. Based on them, you can build the path to each image (or the URL) easily when needed. Warning: Do not save the full path to the documents directory, especially if you’re testing on Simulator; paths are changing on each build. Save the file name only.
Additionally, if you’re going to use a struct like the one shown above, you could implement small but super convenient functions that will be responsible for saving, loading, or updating your data to the solution (database/file) you’ll eventually select. That way, you’ll have related stuff gathered in one place, and easily accessible (i.e., person.save()).
struct Person {
var name: String?
var answer: String?
var photo: String?
func save() {
…
}
func load() {
…
}
// More functions…
}
Lastly, avoid using UserDefaults, or at least keep just a few non-critical data there. UserDefaults are not meant to keep all data produced by your app. Most importantly, do not use it for saving sensitive data, especially passwords or other stuff like that.
I hope the above will help you make your mind.
I can give you the logic behind coreData and NSUserDefaults, but you will decide which one should be used.
CoreData is usually used as a database. you can create entities and attributes for every entity. Moreover, you can create relations between these entities.
When extracting data from coreData, you can arrange this data using NSSortDescriptor or select a specific record using NSPredicate.
So as you can see CoreData is a database.
While NSUserDefaults is usually used to save a password, username, userID... and such issues that you will regularly use in the app. NSUserDefaults gives you a direct access to the saved variables at any time. However, CoreData will take more time and lines of code to access the entity and make the query.
Now, check which method suits your case more.
I'm using Realm.io as database and I need a select * from all_tables in Realm.
I mean a method returning an RLMArray, but I have not found anything about this.
I need the class reference, such as Realm Browser.
Thanks.
You can use [realm.schema.objectSchema valueForKey:#"className"] to get an NSArray of all of the RLMObject subclasses used in the Realm.
I don't believe this is possible at the moment. You should request it on github. In the mean time you will have to create your own. First you have to know that an RLMArray can only hold one type so if in these different tables there are different types than you can not do the following. It would be as easy as creating your own method for this. It would consist of getting all objects from each table and just inserting them into the RLMArray; If your tables don't have the same type then you will have to use a NSMutableArray or an NSArray.
I'm having some problems storing a change to a complex object. I've done a lot of digging and can't figure this out for the life of me.
From debugging, I can clearly see that the object is correct before storing, but when I retrieve the stored data, it's empty(say the increase of a stat). Specifically here is the breakdown below
StatSheet has ArrayList of Players
Player has ArrayList of Stats
ArrayList of StatSheets -> ArrayList of Players -> ArrayList of Stats
The ArrayList of Stat objects doesn't store after a change is made, no matter what I do. The arraylist of players seems to update fine which confuses me. I have tried changing the update depth to 2, 3, 4, 5, and beyond. I have also tried specifically setting cascadeOnUpdate to true. Can someone please help, I've been at this for days.
It's been a while that I looked at db4o and you didn't give a lot of details about your environment or code but maybe you can look at these solutions:
Do you use web environment? So look at this first answer:
A few questions about working with db4o
Do you use 'commit' when you store your objects? Because after storing and updating process you should commit the changes.
The array list of objects is store but db4o don't know what to do with the inner objects. The ArrayList isn't 'Activatable', so you can't retrieve yours objects.
You must put activationPurpose on every getter/setter of your stored object to enable the activation of object.
As you can't do this on native java objects, DB4O provide you some objects that have been tagged with activationPurpose on there getter/setter : like :
com.db4o.collections.ActivatableArrayList
So every java collection that should be store must be replace with it db4o equivalent (com.db4o.collections.*).
I have an NSMutableArray that contains NSMutableDictionary's. Each dictionary has an AVAsset, an NSURL, an NSString, and two UIImages. I want to save my array to disk so that each time I close and open my app, I can load the array and convert the URLs's to NSData objects in order to play audio and use the AVAssets for some other actions. I know I can save and load my array using initWithContentsOfFile and writeToFile:atomically and this answer is pretty informative: Saving a NSArray. However, that answer was from 2009. Is there a better way of saving and loading an array these days?.
As for the answer you linked, the answer is still valid. And according to it, you cannot store it the way it mentions. This is because array must be plist format compatible in order to be saved like that. When you parse your array down to lowest element hierarchy, you have UIImage which is just an object pointer and doesn't make sense.
One practical way would be store UIImages as separate files, and store their paths as part of your NSMutableDictionary objects. Same holds true for AVAssets. Off course you need to engineer the solution to fully accomplish this goal.
One more way to store non-plist compatible objects is to use archiving and unarchiving feature. Refer to the documentation. Here, make sure that each object in the tree follows protocol NSCoding (Probably, AVAsset in your question does not conform to it, so you need a way to work around it). For an example, see this answer and search the likes of it.
I've got a huge xml File which needs to be parsed.
For different Tags inside the xml, e.g Football Soccer Data, I create NSManagedObjects e.g. SoccerPlayer and so forth.
I also need to use these objects a few times within the parsing method and so I created an Object which finds me the right object for the id I provide.
This works fine for the first game inside the xml but won't work for any one after that.
Could be the problem that I have to delete a few objects as I parse through the xml?
For my XML Parsing Framework, I use TouchXML.
Has anyone else experienced this behaviour before?
I agree with the comment that some code would help -- it's hard to understand exactly what the problem is. Nevertheless, I'll point out that the documentation for NSManagedObject's -objectID says:
Important: If the receiver has not yet been saved, the object ID is a
temporary value that will change when
the object is saved.
So, if you're creating an object, storing it's objectID, saving the context, and then trying to find the object with the objectID that you stored, you're probably going to fail because the temporary objectID was replaced with a permanent one when the context was saved.