单例、NSMutableDictionary 和 plist

Posted 2023-02-23

【中文标题】单例、NSMutableDictionary 和 plist

【英文标题】：Singleton, NSMutableDictionary and plist

【发布时间】：2011-08-24 12:27:16

【问题描述】：

我的应用中有一个名为 SettingsManager 的单例，它应该负责对 plist 的读/写设置。 Singleton 是使用来自 Cocoa With Love (zipped macro file) 的宏合成的。我只是将保留的返回类型从 (void) 更改为 (oneway void)。这是由于 ios 中的新编译器可以处理内存管理。我的问题是，每当我调用 savePrefs 时，调用选择器的按钮都会在活动状态下“挂起”，有时我会收到 EXC_BAD_ACCESS。所以我想我在内存管理方面失败了。令人惊讶的是，当没有可用的 plist 文件时（在应用程序安装后立即），所有默认值都会正确存储并从我的 NSMutableDictionary 中检索。下面是我的代码。将非常感谢您的帮助。

马丁

代码：

1/ 单例标题

#import <Foundation/Foundation.h>

#define SALARY_PREF_KEY @"MonthlySalary"
#define DEFAULT_SALARY [NSNumber numberWithDouble: 0.0]
#define CURRENCY_PREF_KEY @"Currency"
#define DEFAULT_CURRENCY @"USD"
#define EXPENSES_PREF_KEY @"Expenses"
#define DEFAULT_EXPENSES [NSNumber numberWithDouble: 0.0]
#define TIME_INTERVAL_PREF_KEY @"TimeInterval"
#define DEFAULT_INTERVAL [NSNumber numberWithInteger: 2]
#define SAVINGS_PREF_KEY @"Savings"
#define DEFAULT_SAVINGS [NSNumber numberWithDouble: 0.0]

@interface SettingsManager : NSObject 
    NSString *prefsFilePath;
    NSMutableDictionary *settingsDictionary;
    NSNumber *salary;
    NSString *currency;
    NSNumber *expenses;
    NSNumber *timeInterval;
    NSNumber *savings;


+ (SettingsManager *)sharedSettingsManager;

@property (nonatomic, retain) NSString *prefsFilePath;
@property (nonatomic, retain) NSMutableDictionary *settingsDictionary;
@property (nonatomic, retain) NSNumber *salary;
@property (nonatomic, retain) NSString *currency;
@property (nonatomic, retain) NSNumber *expenses;
@property (nonatomic, retain) NSNumber *timeInterval;
@property (nonatomic, retain) NSNumber *savings;

    - (void) savePrefs;
@end

2/ 实施：

#import "SynthesizeSingleton.h"
#import "SettingsManager.h"

@implementation SettingsManager

SYNTHESIZE_SINGLETON_FOR_CLASS(SettingsManager);

@synthesize settingsDictionary, 
            salary, 
            currency, 
            expenses, 
            timeInterval, 
            savings, 
            prefsFilePath;

- (id)init 
    self = [super init];  
    if (self) 
        if (prefsFilePath == nil) 
            NSString *documentsDirectory = [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) objectAtIndex: 0];
            prefsFilePath = [documentsDirectory stringByAppendingPathComponent:@"iEarn.plist"];
        
        if ([[NSFileManager defaultManager] fileExistsAtPath: prefsFilePath]) 
            settingsDictionary = [[NSMutableDictionary alloc] 
                                  initWithContentsOfFile: prefsFilePath];
         
        else 
            settingsDictionary = [[NSMutableDictionary alloc] initWithCapacity: 7];
            [settingsDictionary setObject: DEFAULT_SALARY forKey: SALARY_PREF_KEY];
            [settingsDictionary setObject: DEFAULT_CURRENCY forKey: CURRENCY_PREF_KEY];
            [settingsDictionary setObject: DEFAULT_EXPENSES forKey: EXPENSES_PREF_KEY];
            [settingsDictionary setObject: DEFAULT_INTERVAL forKey: TIME_INTERVAL_PREF_KEY];
            [settingsDictionary setObject: DEFAULT_SAVINGS forKey: SAVINGS_PREF_KEY];
            [settingsDictionary writeToFile: prefsFilePath atomically: YES];
        
        self.salary = [settingsDictionary objectForKey:SALARY_PREF_KEY];
        self.currency = [settingsDictionary objectForKey:CURRENCY_PREF_KEY];
        self.expenses = [settingsDictionary objectForKey:EXPENSES_PREF_KEY];
        self.timeInterval = [settingsDictionary objectForKey:TIME_INTERVAL_PREF_KEY];
        self.savings = [settingsDictionary objectForKey:SAVINGS_PREF_KEY];
    
    return self;


- (void) savePrefs 
    [settingsDictionary setObject: salary forKey: SALARY_PREF_KEY];
    [settingsDictionary setObject: currency forKey: CURRENCY_PREF_KEY];
    [settingsDictionary setObject: expenses forKey: EXPENSES_PREF_KEY];
    [settingsDictionary setObject: timeInterval forKey: TIME_INTERVAL_PREF_KEY];
    [settingsDictionary setObject: savings forKey: SAVINGS_PREF_KEY];
    [settingsDictionary writeToFile: prefsFilePath atomically: YES];   


- (void) dealloc 
    [settingsDictionary dealloc];
    [super dealloc];

@end

3/ 我怎么称呼savePrefs

- (IBAction)saveButtonPressed:(id)sender 
    [[SettingsManager sharedSettingsManager] setSalary: [NSNumber numberWithDouble: [salary.text doubleValue]]];
    [[SettingsManager sharedSettingsManager] setCurrency: currency.text];
    [[SettingsManager sharedSettingsManager] setExpenses: [NSNumber numberWithDouble: [expenses.text doubleValue]]];
    [[SettingsManager sharedSettingsManager] setTimeInterval: [NSNumber numberWithInt: [intervalStepper value]]];
    [[SettingsManager sharedSettingsManager] setSavings: [NSNumber numberWithDouble: [savings.text doubleValue]]];
    [[SettingsManager sharedSettingsManager] savePrefs];

【参考方案1】：

您似乎直接访问了prefsFilePath 实例变量，而不是使用它的访问器：

prefsFilePath = [documentsDirectory stringByAppendingPathComponent:@"iEarn.plist"];

存储的值是自动释放的，所以在当前池耗尽后，引用不再有效。相反，您应该使用：

self.prefsFilePath = [documentsDirectory stringByAppendingPathComponent:@"iEarn.plist"];

或

prefsFilePath = [[documentsDirectory stringByAppendingPathComponent:@"iEarn.plist"] retain];

注意：您可以为所有属性访问添加前缀以避免出现问题，或者rename the instance variables。

【讨论】：

非常感谢！它挽救了这个问题。我实际上是在代码中到处寻找错误，但在 prefsFilePath 分配中......由于我来自 Java，仍然需要学习很多关于内存管理的知识。但是与强制 GC 运行相比，拥有更低级别的控制感觉是正确的。再次感谢！