I have seen some guides that say to do this, and others that say setting initial values and keys of NSUserDefaults this way will cause problems when an app is updated. I'm hoping I can definitively answer that here. In my appdelegate didFinishLaunchingWithOptions method I have:
NSUserDefaults *defaults = [NSUserDefaults standardUserDefaults];
if (![defaults integerForKey:#"totalDays"]) {
// if there is no value for the key, set it to 1
[defaults setInteger:0 forKey:#"totalDays"];
}
if (![defaults objectForKey:#"currentDate"]) {
[defaults setObject:#"32 01" forKey:#"currentDate"];
}
if (! [defaults boolForKey:#"marked"]) {
[defaults setBool:NO forKey:#"marked"];
}
if (![defaults arrayForKey:#"checkedrows"]) {
NSMutableArray *arr1 = [NSMutableArray arrayWithArray:[defaults arrayForKey:#"checkedrows"]];
}
[defaults synchronize];
It might also be helpful to note, you don't "need" default values in there to use them. It might save you time from having to check them for null or zero values later in the app.
As the other answer stated, once values are saved to user defaults, it should persist from update to update and backup to backup. I've been using them for years with no issues with lost or corrupted data.
The data stored in the user defaults are save if the user updates the app. You will not get any problems with your code after an update.
You should not set the default values at all! Instead, use the handy method NSUserDefaults provides for exactly this purpose: -registerDefaults:. Call it early in your program's startup with a dictionary of the default values.
The advantage of this is that because -registerDefaults: is transient, you can tell the difference between "the user hasn't customized this preference" and "the user explicitly set this preference to the default value", which is important if you change default settings in a newer version of the program. It's also a little faster due to not needing to save to the disk.
Related
I am having a problem in my sprite kit app where my NSUserDefaults variable is not working. In createSceneContents (which I know is being called)
if (![defaults objectForKey:#"obj"]) {
difficultyLabel.text = #"Difficulty: Easy";
[defaults setObject:#"Easy" forKey:#"obj"];
} else {
difficultyLabel.text = [NSString stringWithFormat:#"Difficulty: %#", [defaults objectForKey:#"diff"]];
}
and then when you click on the SKLabelNode to change the difficulty and this code is being called
if ([label.text isEqualToString:#"Difficulty: Easy"]) {
label.text = #"Difficulty: Hard";
[defaults setObject:#"Hard" forKey:#"obj"];
NSLog(#"%#",[defaults objectForKey:#"obj"]);
} else {
label.text = #"Difficulty: Easy";
[defaults setObject:#"Easy" forKey:#"obj"];
NSLog(#"%#",[defaults objectForKey:#"obj"]);
but when I stop the program and run it again, it always just says Difficulty: Easy. Any suggestions?
As rmaddy's answer explains, NSUserDefaults won't immediately write data to long-term storage.
The values are saved in temporary memory when you call setObject:forKey:, so if you ever try to call objectForKey: after setObject:forKey:, it will return the value in memory if it exists, and if not, it goes to look for what's been saved to long-term storage.
In the background, the device will eventually save these values to permanent storage. It's something the OS handles, but in normal operation of your app, it shouldn't be necessary to immediately store these values to permanent storage most of the time, so let the OS do this at times when its been optimized to do so (I imagine the OS probably synchs every app's user defaults at once on some regular schedule, and as much as possible, tries to do this when the processor is idle probably).
But with that said, as rmaddy explains, if you've got something that crucially needs to be saved to the permanent storage immediately, you can always call synchronize. Keep in mind though... as long as your app isn't killed while in debug mode, the values you've set to be stored in user defaults will be stored.
But for your own sake, if you want to be absolutely certain, you can put it a call to synchronize in applicationDidEnterBackground as rmaddy suggests. Keep in mind though, this method isn't called if you kill the app.
When you say you "stop the program", what do you mean? Are you running in the debugger and killing the app and rerunning it again? NSUserDefaults doesn't persist your changes immediately. Either call [defaults synchronize] after writing important data or at least add such a call to your app delegate's applicationDidEnterBackground method. And then be sure you put your app in the background before killing it to ensure the data is written first.
To store:
NSString * str = #"name123";
NSUserDefaults *def=[NSUserDefaults standardUserDefaults];
[def setObject:str forKey:#"Key"];
[def synchronize];
NSLog(#"str = = %#",str);
To Retrieve:
NSUserDefaults *def=[NSUserDefaults standardUserDefaults];
NSString *str2 = [def valueForKey:#"Key"];
NSLog(#" Saved str = = %#",str2);
I found another reason why NSUserDefaults not saving,following code can make value in NSUserDefaults not saving:
NSUserDefaults *def= [[NSUserDefaults standardUserDefaults] init];
...
NSUserDefaults *def= [[NSUserDefaults standardUserDefaults] initWithSuiteName:#"123"];
You can search NSUserDefaults in your project to catch those init twice bug.
I had this issue where it was working previously but then wasn't. I couldn't figure it out.
It turned out restarting my mac fixed it. There must be some issue with the prefsd daemon that runs in the background that can cause this I'm guessing
This question already has answers here:
Detect when an iOS app is launched for the first time? [closed]
(7 answers)
Closed 9 years ago.
I am developing an iphone app which ask for one time set up details like user name in the first two screens when the user launches the app for the first time. I dont want these 2 screens to come up when I am launching the app once the user has given the details.
I tried getting the info from internet but I was not able to how to find it out. May be I am missing the technical term or wordings involved in doing this. Could any one please help in accomplishing this scenario. Any sample code would be very helpful.
Thanks for your time
Just set a boolean variable to the user-defaults. The user-defaults is a way to save information to the phone, external from the application, that the app can call upon whenever you want.
Inside your app-delegate when it boots, check the user-defaults for a boolean.
To save a boolean to user-defaults:
NSValue *state = ... //Whatever state you want. NSValue allows for booleans.
NSUserDefaults *defaults = [NSUserDefaults standardUserDefaults];
[defaults setObject:obj forKey:#"notFirstTimeRun"];
[defaults synchronize];
To load the boolean from user-defaults:
NSUserDefaults *defaults = [NSUserDefaults standardUserDefaults];
NSValue *state = [defaults objectForKey:#"notFirstTimeRun"];
Do a check:
if ([state boolValue] == true){
//Has ran before, skip your UIViews or whatever
}
else{
//Has not ran before, do your setup or whatever.
}
What you are looking to do is basically store a flag that dictates whether the user has gone through the setup steps. And upon app launch, you check to see if that flag exists with the respective value to denote whether or not to show a setup screen. NSUserDefaults provides a really simple, easy way of persisting state across sessions.
How about setting a bool in AppDidFinishLaunching. You can check that bool everytime the app is launched and show or hide respective screen based on that.
This is how I would do it:
- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {
if ([[NSUserDefaults standardUserDefaults] boolForKey:#"HasBeenLaunched"]){
// This is not the first time, therefore open app as usual
} else {
// This is the first time, show special views
[[NSUserDefaults standardUserDefaults] setBool:YES forKey:#"HasBeenLaunched"];
[[NSUserDefaults standardUserDefaults] synchronize];
}
}
I add a dictionary to NSUserDefaults and call 'synchronize' method,but when I close my app and reopen it the values which are saved in NSUserDefault are nil.
#define kStartTime #"startTime"
#define kEndTime #"endTime"
NSUserDefaults *defaults=[NSUserDefaults standardUserDefaults];
NSString *startTime=#"08:00";
NSString *endTime=#"18:00";
NSDictionary *dict=[[NSDictionary alloc] initWithObjectsAndKeys:startTime,kStartTime,
endTime,kEndTime,
nil];
[defaults registerDefaults:dict];
[defaults synchronize];
And in the viewDidLoad method I call this:
NSString *startTimeValue=[defaults stringForKey:kStartTime];
the startTimeValue is still nil When I reopen my app in simulator.Is UserDefaults can't save in Simulator???
My point is when i close my app and reopen it in simulator the values are gone.
After I searched the apple document ,I got this.
registerDefaults:.
As is said in Apple Document :Adds the contents of the specified dictionary to the registration domain.
*The contents of the registration domain are not written to disk;*you need to call this method each time your application starts.You can place a plist file in the application's Resources directory and call registerDefaults: with the contents that you read in from that file.
So the function of the registerDefaults: is setting Default values in app,The Default value will not stored in disk by synchronize
I think you try to read the value from NSUserDefaults before you have registered the defaults.
If you register defaults these values are not saved to disk, they will not persist to the next application launch. You have to register the default values every time you launch the app.
When you read an object from NSUserDefaults and you have not saved a value before, the registered default value will be returned. If you have saved a value before, this value will be returned.
In the code you posted you have not saved anything to userDefaults. So the value you have registered as default will be returned. If you haven't registered any values this will return nil.
The code that registers the defaults should be put in a method that runs very early in the application life cycle. I would recommend to use application:didFinishLaunchingWithOptions:
If you want to save multiple values to NSUserDefaults you have to use multiple setObject:forKey: calls.
registerDefaults: can not be used to save multiple keys to NSUserDefaults at the same time!
NSUserDefaults *defaults=[NSUserDefaults standardUserDefaults];
NSDictionary *dict=[[NSDictionary alloc] initWithObjectsAndKeys:startTime,#"kStartTime",
endTime,#"kEndTime",
nil];
[defaults registerDefaults:dict];
[defaults synchronize];
NSString *startTimeValue=[defaults stringForKey:#"kStartTime"];
NSLog(#"%#",startTimeValue);
you need to add keys like #"value" like this.
Now try this code....
I got a problem of my iOS app recently. In my app, an instruction view will appear at the first time of running, then hide from then on. How can I implement this effect?
Try to use this function:
- (BOOL) isFirstRun
{
NSUserDefaults *defaults = [NSUserDefaults standardUserDefaults];
if ([defaults objectForKey:#"isFirstRun"])
{
return NO;
}
[defaults setObject:[NSDate date] forKey:#"isFirstRun"];
[[NSUserDefaults standardUserDefaults] synchronize];
return YES;
}
In your app delegate check for a key in the user defaults (your own custom key, something like "AppWasAlreadyStartedPreviously"). If the key doesn't exist yet, it's the first run. You can show your instruction view and add the key to the user defaults. The next time the user starts the app you'll find the key in the user defaults and know that it's not the first run.
See the documentation of NSUserDefaults.
Store a file and check if the file exsists every time when you start the app. If tr file does not exsists then show intro, and then create the file.
The only way I think is to store a value into a specified file, when run the app, you should check the value first, and then you can deal with the result whether the app has already been run.
I have an iPhone application that does an action. Let's call it X. I'd like to have a pop up that asks the user if they want to rate my application after they have performed action X ten times. How can I keep track of this? Meaning, if they close the application the value will still be available. Do I need to keep a text file and update the value and write to a file each time or is there an easier way?
Use NSUserDefaults.
You can do something like this to retrieve the value:
NSUserDefaults *defaults = [NSUserDefaults standardUserDefaults];
int timesOpened = [defaults integerForKey:#"timesOpened"];
To save a value you do:
NSUserDefaults *defaults = [NSUserDefaults standardUserDefaults];
int timesOpened = [defaults integerForKey:#"timesOpened"];
[defaults setInteger:(timesOpened + 1) forKey:#"timesOpened"];
[defaults synchronize];
See here for more information
Why not just use L0SolicitReview. It does this, only a little bit different (still in line with what you described, just a few extra constraints). Best of all, it's done for you.
Another option is, use SQLite3 which is already included in iOS SDK. This works for people who are more familiar with SQL than Cocoa.