Global NSMutableString

Question

I have a tabbed views where I need to select various options from different tabbed views which should be appended in the same string. For this I want to use a NSMutableString.

After all the options are selected and string is formed as required. I want to access this NSMutableString in the next view which is not tabbed. I think for this I need to declare the NSMutableString as a global variable?

Can someone please help me with this. I am new to objective-c and xcode. Thank you. Any help is much appreciated!

Answer 1

1. You can make it a property of your app delegate
2. You can use a singleton
3. You can use NSUserDefaults
4. You can arrange for all of the "interested party" objects to share some common object (with addressability passed during initialization) that contains a field pointing to your string

And probably several others.

Answer 2

You can use NSUserDefaults for this:

To save: (call before next view loaded in previous view class)

NSUserDefaults *defaults = [NSUserDefaults standardUserDefaults]; 
[defaults setObject:yourString forKey:@"KEYNAMEHERE"];
[defaults synchronize];

To retrieve (call when next view is loaded in the next view's class)

NSUserDefaults *defaults = [NSUserDefaults standardUserDefaults]; 
NSMutableString *string = [defaults objectForKey:@"KEYNAMEHERE"];

Answer 3

Another option would be to have a singleton object, especially useful if you have more than just one variable you want shared.

Here's a good post about doing singletons right: http://lukeredpath.co.uk/blog/a-note-on-objective-c-singletons.html

Basically you'd have write a very simple class something like:

State.h:

@interface State : NSObject

@property (atomic, strong) NSMutableString *mystring;
+ (id)sharedInstance;

@end

State.m:

#import "State.h"
@implementation State

@synthesize mystring;

+ (id)sharedInstance
{
  static dispatch_once_t pred = 0;
  __strong static id _sharedObject = nil;
  dispatch_once(&pred, ^{
    _sharedObject = [[self alloc] init]; // or some other init method
  });
  return _sharedObject;
}
@end

and then whenever you need it you could do:

import "State.h"

[State sharedInstance].mystring

Even simpler you can use singleton macro from here: https://gist.github.com/1057420#gistcomment-63896

I've personally found this pattern to be extremely useful.