The best way to save global variables in an iPhone application

Question

I am new to iPhone development, so I want to ask what is the best way to save global variables and constants that many classes can access?

Should I store them in the application delegate or is there a better way that I don't know?

thanks

Answer 1

Saving them as an application delegate is one solution, although it is not particularly elegant to insert everything into a class whose purpose is to really respond to events related to the application.

For constants, you can simply create header files and use #define or const , and then include header files wherever you need constants.

For global variables, you can create a singleton class with static variables. There are many macros that can synthesize singletones for classes. Here is an example from Google Toolbox for Mac:

 // // GTMObjectSingleton.h // Macro to implement methods for a singleton // // Copyright 2005-2008 Google Inc. // // Licensed under the Apache License, Version 2.0 (the "License"); you may not // use this file except in compliance with the License. You may obtain a copy // of the License at // // http://www.apache.org/licenses/LICENSE-2.0 // // Unless required by applicable law or agreed to in writing, software // distributed under the License is distributed on an "AS IS" BASIS, WITHOUT // WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the // License for the specific language governing permissions and limitations under // the License. // #define _GTMDevAssert(condition, ...) \ do { \ if (!(condition)) { \ [[NSAssertionHandler currentHandler] \ handleFailureInFunction:[NSString stringWithUTF8String:__PRETTY_FUNCTION__] \ file:[NSString stringWithUTF8String:__FILE__] \ lineNumber:__LINE__ \ description:__VA_ARGS__]; \ } \ } while(0) /// This macro implements the various methods needed to make a safe singleton. // /// This Singleton pattern was taken from: /// http://developer.apple.com/documentation/Cocoa/Conceptual/CocoaFundamentals/CocoaObjects/chapter_3_section_10.html /// /// Sample usage: /// /// GTMOBJECT_SINGLETON_BOILERPLATE(SomeUsefulManager, sharedSomeUsefulManager) /// (with no trailing semicolon) /// #define GTMOBJECT_SINGLETON_BOILERPLATE(_object_name_, _shared_obj_name_) \ static _object_name_ *z##_shared_obj_name_ = nil; \ + (_object_name_ *)_shared_obj_name_ { \ @synchronized(self) { \ if (z##_shared_obj_name_ == nil) { \ /* Note that 'self' may not be the same as _object_name_ */ \ /* first assignment done in allocWithZone but we must reassign in case init fails */ \ z##_shared_obj_name_ = [[self alloc] init]; \ _GTMDevAssert((z##_shared_obj_name_ != nil), @"didn't catch singleton allocation"); \ } \ } \ return z##_shared_obj_name_; \ } \ + (id)allocWithZone:(NSZone *)zone { \ @synchronized(self) { \ if (z##_shared_obj_name_ == nil) { \ z##_shared_obj_name_ = [super allocWithZone:zone]; \ return z##_shared_obj_name_; \ } \ } \ \ /* We can't return the shared instance, because it been init'd */ \ _GTMDevAssert(NO, @"use the singleton API, not alloc+init"); \ return nil; \ } \ - (id)retain { \ return self; \ } \ - (NSUInteger)retainCount { \ return NSUIntegerMax; \ } \ - (void)release { \ } \ - (id)autorelease { \ return self; \ } \ - (id)copyWithZone:(NSZone *)zone { \ return self; \ } 

Answer 2

In case you like the variety, here is another one, this one from CocoaWithLove - it talks about why global varnas should scare you here ; probably well read.

 // // SynthesizeSingleton.h // CocoaWithLove // // Created by Matt Gallagher on 20/10/08. // Copyright 2008 Matt Gallagher. All rights reserved. // // Permission is given to use this source code file, free of charge, in any // project, commercial or otherwise, entirely at your risk, with the condition // that any redistribution (in part or whole) of source code must retain // this copyright and permission notice. Attribution in compiled projects is // appreciated but not required. // #define SYNTHESIZE_SINGLETON_FOR_CLASS(classname) \ \ static classname *shared##classname = nil; \ \ + (classname *)shared##classname \ { \ @synchronized(self) \ { \ if (shared##classname == nil) \ { \ shared##classname = [[self alloc] init]; \ } \ } \ \ return shared##classname; \ } \ \ + (id)allocWithZone:(NSZone *)zone \ { \ @synchronized(self) \ { \ if (shared##classname == nil) \ { \ shared##classname = [super allocWithZone:zone]; \ return shared##classname; \ } \ } \ \ return nil; \ } \ \ - (id)copyWithZone:(NSZone *)zone \ { \ return self; \ } \ \ - (id)retain \ { \ return self; \ } \ \ - (NSUInteger)retainCount \ { \ return NSUIntegerMax; \ } \ \ - (void)release \ { \ } \ \ - (id)autorelease \ { \ return self; \ } 

Answer 3

Usually I make the header file Resources.h and save my entire definition. Using a static variable is also a good idea.