在 iPhone 应用程序中保留全局变量的最佳方法

Question

我是 iPhone 开发的新手，所以想问一下，保存可以被许多类访问的全局变量和常量的最佳方法是什么？

我应该将它们保留在应用程序委托中还是有更好的方法我不知道？

谢谢

Answer 1

将它们保留在应用程序委托中是一种解决方案，尽管将所有内容都放入一个真正用于响应与应用程序相关的事件的类中并不是特别优雅。

对于常量，您可以简单地创建头文件并使用#define 或const，然后在需要常量的地方包含头文件。

对于全局变量，您可以使用static 变量创建singleton class。有很多宏可以为类合成单例。以下是 Google Toolbox for Mac 中的一个示例：

//
//  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;                                     \
}

Answer 2

如果你喜欢多样性，这里还有一个，这个来自CocoaWithLove——他在谈论为什么全局变量会吓到你here；可能是一本好书。

//
//  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

通常我会创建一个头文件 Resources.h 并将我的所有定义保存在那里。使用静态变量也是一个好主意。