How do I store program variables in an iPhone application that will survive a program exit?

Question

I need to keep program variable values in an iPhone application when the application is exited. Does the SDK give the programmer any non volitile memory to use? How much is available? Will it be kept thru a power cycle? Through sleep mode? Through a hard reset?

Answer 1

You could write to your app's local storage area or use a sqlite database. Both options are documented here, http://developer.apple.com/iphone/library/codinghowtos/DataManagement/index.html#FILE_MANAGEMENT-WRITE_INFORMATION_LOCALLY

Answer 2

Your best option is to store them to into the your applications SQLite DB instance. Thats as close as you'll get to non volatile memory.

Answer 3

You want to use the NSUserDefaults class to store user settings. It's super easy. They will be persisted across device restarts, power cycles, etc.

Here's a short tutorial to get you started.

Answer 4

There are many options available for storing the data from your app to be used later. Tow of them as pointed out are using NSUserDefaults and SQLite. Another way is to create a file in the "Documents" folder of your app and save your data here. Read the contents of the file the next time the app is launched. This is explained in the Files & Networking guide from Apple

Even if using the database, make sure you create a copy of the database in the Documents folder of your app's sandbox so it persists even when you release an update for your app.

Answer 5

-(void)saveToUserDefaults:(NSString*)myString
{
    NSUserDefaults *standardUserDefaults = [NSUserDefaults standardUserDefaults];

    if (standardUserDefaults) {
     [standardUserDefaults setObject:myString forKey:@"Prefs"];
     [standardUserDefaults synchronize];
    }
}

-(NSString*)retrieveFromUserDefaults
{
    NSUserDefaults *standardUserDefaults = [NSUserDefaults standardUserDefaults];
    NSString *val = nil;

    if (standardUserDefaults) 
     val = [standardUserDefaults objectForKey:@"Prefs"];

    return val;
}