App Icon size of iPhone 6 and iPhone 6 plus : 

NSUserDefaults iPhone/Objective c

iPhone Tutorial – Saving/Retrieving Data Using NSUserDefaults :

The NSUserDefaults class provides a programmatic interface for interacting with the defaults system. The defaults system allows an application to customize its behavior to match a user’s preferences.

At runtime, you use an NSUserDefaults object to read the defaults that your application uses from a user’s defaults database. NSUserDefaults caches the information to avoid having to open the user’s defaults database each time you need a default value. The synchronize method, which is automatically invoked at periodic intervals, keeps the in-memory cache in sync with a user’s defaults database.

Saving to NSUserDefaults :
========================

Basically, all you have to do is load NSUserDefaults, and then tell it to save a value to a specific key. Here is a simple example of writing an integer to NSUserDefaults:

NSUserDefaults *defaults = [NSUserDefaults standardUserDefaults]; [defaults setInteger:101 forKey:@"RollNo"]; 

[defaults synchronize];

As mentioned earlier,
we loaded the NSUserDefaults plist to the object “defaults”. We then told that object to set an integer for the key “RollNo”.
But we know that, we must have to use “synchronize” method to save the value. It isn’t absolutely necessary, because this is called automatically every so often, but if you want to be sure to save the changes to NSUserDefaults right now, this is how.


Other Samples for NSUserDefaults :
NSUserDefaults *prefs = [NSUserDefaults standardUserDefaults];     

// saving an NSString
[prefs setObject:@"IT0809" forKey:@"AccessNo"];
   
// saving an NSInteger
[prefs setInteger:42 forKey:@"RollNo"];
    
// saving a Double
[prefs setDouble:9.99 forKey:@"DoubleKey"];
    
// saving a Float
[prefs setFloat:1.7565671 forKey:@"FloatKey"];
    
[prefs synchronize];

Reading from NSUserDefaults
========================

Reading is even easier, as shown below:

NSUserDefaults *defaults = [NSUserDefaults standardUserDefaults];
NSInteger theHighScore = [defaults integerForKey:@"RollNo"];

Other Samples for NSUserDefaults :

NSUserDefaults *prefs = [NSUserDefaults standardUserDefaults];

// getting an NSString


NSString *myString = [prefs stringForKey:@"AccessNo"];

// getting an NSInteger


NSInteger myInt = [prefs integerForKey:@"RollNo"];

// getting an Float


float myFloat = [prefs floatForKey:@"FloatKey"];

Delete all keys from a NSUserDefaults dictionary iPhone :

- (void)resetDefaults {

     NSUserDefaults * defs = [NSUserDefaults standardUserDefaults];
     NSDictionary * dict = [defs dictionaryRepresentation];
     for (id key in dict) {
           [defs removeObjectForKey:key];
     }
     [defs synchronize];
}

Refer this Links :

1. http://www.icodeblog.com/2008/10/03/iphone-programming-tutorial-savingretrieving-data-using-nsuserdefaults/
2. http://ios-blog.co.uk/tutorials/quick-tips/storing-data-with-nsuserdefaults/

Common Error of iOS : 

1. xcode timed out waiting for app to launch:

Reason 1. : It turned out I was using my Distribution Profile instead of the Developer Profile in Debug mode. You can check the Profile you are using by going to Build Settings->Code Signing Entity.
Make sure you are using your Developer Profile in Beta and Debug mode.

Reason 2. : I had this problem when I used a Distribution certificate instead of Developer one when running the app from Xcode. You may check it out your target --> Build Settings --> Code signing.

Check Below Links:

• http://stackoverflow.com/questions/22683419/xcode-5-could-not-launch-process-launch-failed-timed-out-waiting-for-app-to-la
• http://stackoverflow.com/questions/13048321/xcode-timed-out-waiting-for-app-to-launch
• http://stackoverflow.com/questions/14659094/xcode-4-6-error-timed-out-waiting-for-app-to-launch