不知怎的，我的单例属性被释放了

Question

我有一个名为 PoolManager 的单例对象，它在 plist 中加载和保存一些数据。在我的程序中，当需要了解我的池时，它会向 [PoolManager sharedPoolManager] 询问其属性。我有一个负责设置这些属性的视图，而所有其他视图只是从中读取。一切都工作正常，然后不知为何，它开始崩溃。我设置了 NSZombieEnabled = YES 并可以看到，当我访问两个 NSString 属性之一时，它们似乎已被释放。调试器消息是： *** -[CFString respondsToSelector:]: message sent to deallocated instance 0x5a336d0

我尝试返回到之前的快照，一切正常，但仍然如此。我什至使用 TimeMachine 回到昨天的项目，它也做到了。我很困惑。

这是单例对象代码...它的 surface 和 shape 字符串显然是僵尸。对于所有 NSLogs 表示抱歉

---

//  MyPoolSingleton.h

#import <Foundation/Foundation.h>

#define kFileName @"data.plist"

@interface PoolManager : NSObject {
    float   volume;
    float length;
    float width;
    float depth;    
    NSString *surface;
    NSString *shape;
    BOOL isMetric;
    int fcTarget;
    int cyaTarget;
    int taTarget;
    int chTarget;
    int saltTarget;
}

@property float volume;
@property float length;
@property float width;
@property float depth;
@property (nonatomic, retain) NSString *surface;
@property (nonatomic, retain) NSString *shape;
@property BOOL isMetric;
@property int fcTarget;
@property int cyaTarget;
@property int taTarget;
@property int chTarget;
@property int saltTarget;

+ (PoolManager*)sharedPoolManager;
- (void)retrieveState;
- (void)saveState;
- (NSString*)dataFilePath;

@end

---

//  MyPoolSingleton.m

#import "PoolManager.h"

@implementation PoolManager

@synthesize volume;
@synthesize length;
@synthesize width;
@synthesize depth;
@synthesize surface;
@synthesize shape;
@synthesize isMetric;
@synthesize fcTarget;
@synthesize cyaTarget;
@synthesize taTarget;
@synthesize chTarget;
@synthesize saltTarget;

static PoolManager* _sharedPoolManager = nil;

+ (PoolManager*)sharedPoolManager {
    @synchronized([PoolManager class])
    {
        if (!_sharedPoolManager)
            [[self alloc] init];
        return _sharedPoolManager;
    }
    return nil;
}

+ (id)alloc {
    @synchronized([PoolManager class])
    {
        NSAssert(_sharedPoolManager == nil, @"Attempted to allocate a second instance of a singleton.");
        _sharedPoolManager = [super alloc];
        return _sharedPoolManager;
    }
    return nil;
}

- (id)init {
    self = [super init];
    return self;
}

- (void)retrieveState {
    NSLog(@"--retrieveState");
    NSString *filePath = [self dataFilePath];
    if ([[NSFileManager defaultManager] fileExistsAtPath:filePath]) {
        NSLog(@"    fileExistsAtPath: reading array from plist");
        NSArray *array = [[NSArray alloc] initWithContentsOfFile:filePath];
        volume = [[array objectAtIndex:0] floatValue];
            NSLog(@"      reading array: volume = %1.1f", volume);
        length = [[array objectAtIndex:1] floatValue];
            NSLog(@"      reading array: length = %1.1f", length);
        width = [[array objectAtIndex:2] floatValue];
            NSLog(@"      reading array: width = %1.1f", width);
        depth = [[array objectAtIndex:3] floatValue];
            NSLog(@"      reading array: depth = %1.1f", depth);
        self.surface = [array objectAtIndex:4];
            NSLog(@"      reading array: surface = %@", surface);
        self.shape = [array objectAtIndex:5];
            NSLog(@"      reading array: shape = %@", shape);
        isMetric = [[array objectAtIndex:6] boolValue];
            NSLog(@"      reading array: isMetric = %d", isMetric);
        fcTarget = [[array objectAtIndex:7] intValue];
            NSLog(@"      reading array: fcTarget = %d", fcTarget);
        cyaTarget = [[array objectAtIndex:8] intValue];
            NSLog(@"      reading array: cyaTarget = %d", cyaTarget);
        taTarget = [[array objectAtIndex:9] intValue];
            NSLog(@"      reading array: taTarget = %d", taTarget);
        chTarget = [[array objectAtIndex:10] intValue];
            NSLog(@"      reading array: chTarget = %d", chTarget);
        saltTarget = [[array objectAtIndex:11] intValue];
            NSLog(@"      reading array: saltTarget = %d", saltTarget);
        [array release];
    }
    else {
        NSLog(@"    !fileExistsAtPath: intitializing values to nil/zero");
        volume = 0.0;
        length = 0.0;
        width = 0.0;
        depth = 0.0;
        surface = @"";
        shape = @"";
        isMetric = NO;
        fcTarget = 0.0;
        cyaTarget = 0.0;
        taTarget = 0.0;
        chTarget = 0.0;
        saltTarget = 0.0;
    }
}

- (void)saveState {
    NSLog(@"--saveState");
    NSMutableArray *array = [[NSMutableArray alloc] init];
        NSLog(@"      building array: volume = %1.1f", volume);
    [array addObject:[NSNumber numberWithFloat:volume]];
        NSLog(@"      building array: length = %1.1f", length);
    [array addObject:[NSNumber numberWithFloat:length]];
        NSLog(@"      building array: width = %1.1f", width);
    [array addObject:[NSNumber numberWithFloat:width]];
        NSLog(@"      building array: depth = %1.1f", depth);
    [array addObject:[NSNumber numberWithFloat:depth]];
        NSLog(@"      building array: surface = %@", surface);
    [array addObject:surface];
        NSLog(@"      building array: shape = %@", shape);
    [array addObject:shape];
        NSLog(@"      building array: isMetric = %d", isMetric);
    [array addObject:[NSNumber numberWithBool:isMetric]];
        NSLog(@"      building array: fcTarget = %d", fcTarget);
    [array addObject:[NSNumber numberWithInt:fcTarget]];
        NSLog(@"      building array: cyaTarget = %d", cyaTarget);
    [array addObject:[NSNumber numberWithInt:cyaTarget]];
        NSLog(@"      building array: taTarget = %d", taTarget);
    [array addObject:[NSNumber numberWithInt:taTarget]];
            NSLog(@"      building array: chTarget = %d", chTarget);
    [array addObject:[NSNumber numberWithInt:chTarget]];
        NSLog(@"      building array: saltTarget = %d", saltTarget);
    [array addObject:[NSNumber numberWithInt:saltTarget]];

    [array writeToFile:[self dataFilePath] atomically:YES];
    [array release];
}    

- (NSString*)dataFilePath {
    NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
    NSString *documentsDirectory = [paths objectAtIndex:0];
    return [documentsDirectory stringByAppendingPathComponent:kFileName];
}

- (void)dealloc {
    [shape release], shape = nil;
    [surface release], surface = nil;
    [super dealloc];
}

@end

Answer 1

objectAtIndex: 给出一个自动释放的对象。您应该保留它，或者在设置它们时使用属性访问器 self.surface = ... 和 self.shape = ... 。

Answer 2

就我个人而言，我更喜欢以下单例模式：（

+ (id) sharedPoolManager
{
    static id sharedPoolManager = nil;
    @synchronized (self) {
        if (sharedPoolManager == nil) {
             sharedPoolManager = [self new];
        }
    }
    return sharedPoolManager;
}

- (id) init
{
    if ((self = [super init]) != nil) {
         // Initialize ... nothing special here ...
    }
    return self;
}

请注意，类方法中的 self 相当于 [SomeClass class]）

上面更简洁，我更喜欢保留任何init 和 alloc 之外的单例代码，因为如果需要，我还可以创建多个实例。例如在单元测试中。

就我个人而言，我认为您不必保护程序员不创建多个实例。契约很明确：sharedPoolManager 返回一个单例实例。如果这就是您想要/需要的，那么就使用它。否则以通常的方式创建实例。