NSUserDefaults is such an easy and convenient way to persist data on a device, and while it is encouraged as use for basic settings, I wonder, is there a practical limit to what you should use it for?
Suppose you have a large dictionary of many objects, 1000, and each of those objects is itself a dictionary with simple text strings as values. Overall, this big dictionary is probably not too large, since it only contains text, even if a fair amount of it.
Is it O.K. to use NSUserDefaults for something like this, your main data model?
Why not just store that as an NSDictionary in a file?
See this post for a nice way to save your file as a plist:
Save NSDictionary to plist
and getting it back is as easy as this:
NSDictionary *dict = [NSDictionary dictionaryWithContentsOfFile:fileName];
Related
i need to store some objects from table.
It will be no more than 100 objects.
Is it good way to store it like array in NSUserDefaults? Or there is any better way?
Although you can store this is NSUserDefaults using [[NSUserDefaults standardUserDefaults] arrayForKey:#"key"]; you probably shouldn't. Defaults was designed to store VERY small ammounts of data, like a users preferences (thus the name). If you wish to store more data than this, then you may want to look into .plists, NSDocumentDirectory, Core-Data, or SQLite databases.
The better way would be to serialize it as a binary blob on disk using NSArrays writeToFile:atomically: or writeToURL:atomically:. NSUserDefaults aren't stored as binary and thus need extra parsing time upon loading, and extra time to write out to disk. NSUserDefaults is also not designed to hold large amounts of data but for a small set of settings data.
Store all custom data in NSDictionary or NSArray.
Now save dictionary or array with custom data in document directory follow this link
no Storing data on NSUserDefaults is not good, because it can cause a serious hack.
instead of it you can use AppDelegate to store data globally.
I'm trying to create a save & load module in my app. So the user can save some specific info and then load it at any point in time.
What I'm saving is an array of NSMutableStrings. I'm creating an iPad app so the saved info will be presented in a popover with a TableView.
So, here's the question. I would like to populate that tableView with my saved arrays, and for that I need to store my arrays somewhere. I'm new to objective-c and programming in general, and would like your advice on what's the best way of doing that.
Should I use a plist to store those arrays with Keys, so the keys will be the names that the user introduces when saving and also the name of the tableView cells? or maybe a simple NSMutableDictionary will do?
Please advise.
This answer might help you. Using Core Data might be overkill here, and saving to a plist is extremely easy. This is Benoît's answer from the linked question:
NSString *error;
NSString *rootPath = [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory,
NSUserDomainMask, YES) objectAtIndex:0];
NSString *plistPath = [rootPath stringByAppendingPathComponent:#"yourFile.plist"];
NSData *plistData = [NSPropertyListSerialization dataFromPropertyList:rootObj
format:NSPropertyListXMLFormat_v1_0 errorDescription:&error];
if(plistData) {
[plistData writeToFile:plistPath atomically:YES];
}
else {
NSLog(#"Error : %#",error);
[error release];
}
where rootObj is the object you wish to serialize, in this case, your array/dictionary.
Also, if you are going to be read/writing to this data frequently during the course of your app, using a singleton which can make a huge difference performance-wise instead of constantly reading/writing from/to a file. You can load all of your data into the singleton on app-launch and save it upon applicationWillTerminate.
To answer your array/dictionary question, it depends on how you are obtaining your strings and how you want them to be ordered. Sorting an array is extremely easy, as you can see in this answer.
Sergey, based on your description, I would advise you look into using Core Data for data storage.
https://developer.apple.com/library/mac/#documentation/cocoa/conceptual/coredata/cdprogrammingguide.html
In addition to storing data, Apple has extended the use of Core Data in all sorts of neat ways, including the use of stored data to populate a UITableViewController through the use of NSFetchedResultsController
https://developer.apple.com/library/ios/#documentation/CoreData/Reference/NSFetchedResultsController_Class/Reference/Reference.html
That's it, give that a read and you should be well on your way.
I can go either way on this for this project, but I'm curious if using a plist to store some data is going to be more or less efficient than just keeping a plist in the documents folder. The data is about 50 strings/dictionaries.
In both cases the data gets persisted using some file IO so disk access should be similar.
However, the plist seems like a little more work.
NSUserDefaults is a plist (that is why only plist types can be stored in it). So ultimately there isn't going to be much difference in efficiency (whatever you mean by that). Your consideration should rather be where it is appropriate to keep this data. Don't keep it in the Document folder unless it is appropriate for storage in iCloud, says Apple; it will be backed up when the user backs up the device, and will subtract from the user's quota, so you need to be sparing of what you keep there.
In one of my own apps, where I download a bunch of data from an RSS feed and present it to the user, I store the data in the user defaults, because it is part of the app's persistent state the next time it appears. My data isn't a document; it's the app's state. That's my reasoning, and I'd suggest you might reason along similar lines...
In my opinion, plist are much simpler to use than NSuserDefaults. Afterall, a dictionary can save itself as a plist. As for efficiency, they sould be the same as NSUserDefaults stores everything as a plist but provides more services such as comparing which key/values pair have changed compared to a provided set of key/values default pairs.
You may want to consider JSON using JSONKit. Some tests show it's faster than a binary plist, if speed is your primary concern. The API is dead simple because it creates a category on NSDictionary and NSArray. Calling -(NSData *)JSONData on either of those objects returns an NSData object ready to save.
I want to save data locally but i do not know which method is better nsdictionary or plist?Can anyone tell which method is better and why?
Thanks in advance!
I think maybe what you meant to ask is which is better, plist or binary. If you save an NSDictionary to file using writeToFile: it will be stored as a plist. So in that sense there is zero difference between the two.
However, you also have the option of converting an NSDictionary instance into a serialized NSData representation, and then storing the serialized data as a binary file.
As for which is better and why, that depends upon what you want to do. The API for converting an NSDictionary to/from a plist file is more convenient to use than the API for serializing and reconstructing to/from NSData. However, storing an NSDictionary as a plist file only works if everything in the dictionary is a plist object (instances of NSData, NSDate, NSNumber, NSString, NSArray, or NSDictionary) and if all of your keys are of type NSString. Otherwise your writeToFile: call will fail with frustratingly little information being provided about why.
So if your data structure meets the requirements for being stored as a plist and you cannot foresee it ever being changed such that it would no longer meet the requirements then you may find it more convenient storing it as a plist. Otherwise your only option is to do a binary serialization and storage using NSData. You may prefer this latter option if you want to have code that cannot be accidentally broken by someone sticking a non-plist-object in your data structure.
I have a simple problem:
I add an object to an NSArray, then I add an object to it then I use the NSUserDefaults way to save the array, but it doesn't work, I mean the array isn't saved and the console sends me this messange:
2011-03-21 23:09:53.994 Project[10490:207] * -[NSUserDefaults setObject:forKey:]: Attempt to insert non-property value '(
""
)' of class '__NSArrayM'.
does anybody know how can I fix this.
NSUserDefaults only allows you to save basic lightweight objects; for example NSString, NSNumber and NSData. If you want to add another class, you'll have to shoehorn it into an NSData object beforehand. This is pretty simple, usually just a call to [NSKeyedArchiver archivedDataWithRootObject:array];. Note that the objects in the array must implement the NSCoding protocol, which you'll have to add to any of your own custom classes if that's what you want to save.
Also keep in mind NSUserDefaults is meant for lightweight preferences, not application data. If you have a large array of objects, you might be better served by archiving it to its own file or using Core Data (if you feel comfortable using something a little more advanced).
The only types you can save in NSUserDefaults are property list types: NSString, NSDate, NSArray, NSDictionary, NSNumber, NSData. You're probably trying to save an array of objects that aren't one of these types.