在Objective-C中使用全局变量

Question

首先,我尝试了几乎所有在stackoverflow中给出的解决方案,但我没有成功实现全局变量,我甚至做了一步一步的教程,但我仍然得到相同的错误.

继承人的问题:

我有一个包含多个视图的程序,我想在所有视图上使用变量,所以我使用了全局变量,

我有:

GlobalVars.h

#import <UIKit/UIKit.h>
extern NSArray *truckBoxes;
extern NSArray *farmerlist;
extern NSString *farmerCardNumber;

extern NSString *fName;

@interface GlobalVars : NSObject
{
}

@end

GlobalVars.m

#import "GlobalVars.h"

NSArray *farmerlist;
NSArray *truckBoxes;
NSString *farmerCardNumber;
NSString *fName;
@implementation GlobalVars
{

}
@end

我将该文件包含在类中(连接到视图控制器):在我添加的.h文件下 #import "GlobalVars.h

我可以访问farmerlist和truckBoxes从应用程序,但无法访问fName或farmerCardNumber.

我可以写farmerCardNumber同一个视图并从中读取,但如果我稍后尝试从另一个视图访问它,我会得到

2013-10-26 11:11:45.612 C3Cms[10427:70b] Branch : 11558
2013-10-26 11:11:59.459 C3Cms[10427:70b] -[__NSArrayM length]: unrecognized selector sent to instance 0x8b7fbc0
2013-10-26 11:11:59.463 C3Cms[10427:70b] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[__NSArrayM length]: unrecognized selector sent to instance 0x8b7fbc0'
*** First throw call stack:
(
    0   CoreFoundation                      0x02a3b5e4 __exceptionPreprocess + 180
    1   libobjc.A.dylib                     0x014d58b6 objc_exception_throw + 44
    2   CoreFoundation                      0x02ad8903 -[NSObject(NSObject) doesNotRecognizeSelector:] + 275
    3   CoreFoundation                      0x02a2b90b ___forwarding___ + 1019
    4   CoreFoundation                      0x02a2b4ee _CF_forwarding_prep_0 + 14
    5   Foundation                          0x00f0db2d -[NSConcreteMutableAttributedString replaceCharactersInRange:withString:] + 39
    6   Foundation                          0x00f0e79a -[NSConcreteMutableAttributedString initWithString:attributes:] + 293
    7   UIKit                               0x001e8116 -[UILabel _setText:] + 97
    8   UIKit                               0x001e82d4 -[UILabel setText:] + 40
    9   C3Cms                               0x00001c1d -[printForm viewDidLoad] + 77
    10  UIKit                               0x0014e9a8 -[UIViewController loadViewIfRequired] + 696
    11  UIKit                               0x0014ec44 -[UIViewController view] + 35
    12  UIKit                               0x00168a72 -[UINavigationController _startCustomTransition:] + 778
    13  UIKit                               0x00175757 -[UINavigationController _startDeferredTransitionIfNeeded:] + 688
    14  UIKit                               0x00176349 -[UINavigationController __viewWillLayoutSubviews] + 57
    15  UIKit                               0x002af39d -[UILayoutContainerView layoutSubviews] + 213
    16  UIKit                               0x000a5dd7 -[UIView(CALayerDelegate) layoutSublayersOfLayer:] + 355
    17  libobjc.A.dylib                     0x014e781f -[NSObject performSelector:withObject:] + 70
    18  QuartzCore                          0x030d772a -[CALayer layoutSublayers] + 148
    19  QuartzCore                          0x030cb514 _ZN2CA5Layer16layout_if_neededEPNS_11TransactionE + 380
    20  QuartzCore                          0x030cb380 _ZN2CA5Layer28layout_and_display_if_neededEPNS_11TransactionE + 26
    21  QuartzCore                          0x03033156 _ZN2CA7Context18commit_transactionEPNS_11TransactionE + 294
    22  QuartzCore                          0x030344e1 _ZN2CA11Transaction6commitEv + 393
    23  QuartzCore                          0x03034bb4 _ZN2CA11Transaction17observer_callbackEP19__CFRunLoopObservermPv + 92
    24  CoreFoundation                      0x02a0353e __CFRUNLOOP_IS_CALLING_OUT_TO_AN_OBSERVER_CALLBACK_FUNCTION__ + 30
    25  CoreFoundation                      0x02a0348f __CFRunLoopDoObservers + 399
    26  CoreFoundation                      0x029e13b4 __CFRunLoopRun + 1076
    27  CoreFoundation                      0x029e0b33 CFRunLoopRunSpecific + 467
    28  CoreFoundation                      0x029e094b CFRunLoopRunInMode + 123
    29  GraphicsServices                    0x029979d7 GSEventRunModal + 192
    30  GraphicsServices                    0x029977fe GSEventRun + 104
    31  UIKit                               0x0003b94b UIApplicationMain + 1225
    32  C3Cms                               0x00002882 main + 130
    33  libdyld.dylib                       0x019bc70d start + 1
)
libc++abi.dylib: terminating with uncaught exception of type NSException

Answer 1

实现全局变量并管理它们的生命周期(即它们被初始化)甚至提供全局方法的一种方法是实现暴露这些变量/方法并使用单例模式的类:

GlobalVars.h:

#import <Foundation/Foundation.h>

@interface GlobalVars : NSObject
{
    NSMutableArray *_truckBoxes;
    NSMutableArray *_farmerlist;
    NSString *_farmerCardNumber;
    NSString *_fName;
}

+ (GlobalVars *)sharedInstance;

@property(strong, nonatomic, readwrite) NSMutableArray *truckBoxes;
@property(strong, nonatomic, readwrite) NSMutableArray *farmerList;
@property(strong, nonatomic, readwrite) NSString *farmerCardNumber;
@property(strong, nonatomic, readwrite) NSString *fName;

@end

GlobalVars.m:

#import "GlobalVars.h"

@implementation GlobalVars

@synthesize truckBoxes = _truckBoxes;
@synthesize farmerList = _farmerList;
@synthesize frameCardNumber = _frameCardNumber;
@synthesize fName = _fName;

+ (GlobalVars *)sharedInstance {
    static dispatch_once_t onceToken;
    static GlobalVars *instance = nil;
    dispatch_once(&onceToken, ^{
        instance = [[GlobalVars alloc] init];
    });
    return instance;
}

- (id)init {
    self = [super init];
    if (self) {
        _truckBoxes = [[NSMutableArray alloc] init];
        _farmerlist = [[NSMutableArray alloc] init];
        // Note these aren't allocated as [[NSString alloc] init] doesn't provide a useful object
        _farmerCardNumber = nil;
        _fName = nil;
    }
    return self;
}

@end

然后,您可以使用这样的全局变量,例如:

GlobalVars *globals = [GlobalVars sharedInstance];
globals.fName = @"HelloWorld.txt";
[globals.farmerList addObject:@"Old Macdonald"];
[self processList:[globals farmerList]];

但请考虑:

• 你不需要像这样使用全局变量; 您应该能够创建一个必要时创建的模型对象,并将其引用传递给视图.这是MVC.
• 您还发布了一个与Objective-C极为常见的无关问题的堆栈跟踪; 一旦你意识到它是什么,只有你能解决这个错误.