views:

83

answers:

3

Hi everyone, I'm new to iPhone development so want to ask, what is the best way to keep global variables and constants which can be accessed by many classes?

Shall I keep them in app delegate or there is a better way which I don't know?

Thanks

+2  A: 

Keeping them in the app delegate is one solution, though it's not particularly elegant to shove everything into a class whose purpose is really to respond to events related to the application.

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

For global variables, you can create a singleton class with static variables. There are a lot of macros out there that can synthesize singletons for classes. Here's an example from the 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's 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;                                     \
}
anshuchimala
+2  A: 

In case you like variety, here's another one, this one from CocoaWithLove -- he's talking about why global vars should scare you here; probably a good 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; \
}
Kalle
A: 

Usually I make a header file Resources.h and keep all my definition there. Using static variable is also a good idea.

karim
and how do u define constants there? like this?#define MY_CONST @"my constant"
Burjua