我有一个名为PoolManager的单例对象，可以在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，它会询问[PoolManager sharedPoolManager]它的属性。我有一个视图负责设置这些属性，而其他所有其他属性只是从中读取。一切正常，然后无缘无故地说，它开始崩溃了。我设置了NSZombieEnabled = YES，可以看到当我访问其中一个NSString属性时，它们似乎已被释放。调试器消息为：*** -[CFString respondsToSelector:]: message sent to deallocated instance 0x5a336d0
我尝试回到之前的快照，其中一切正常，但仍然会这样做。我甚至使用TimeMachine从昨天开始回到项目中，它也是如此。我很困惑。
这是单例对象代码......显然是僵尸的surface和shape字符串。抱歉所有NSLogs
// 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
答案 0 :(得分：5)
objectAtIndex:给出一个自动释放的对象。您应该保留它，或者在设置属性访问者时使用属性访问者self.surface = ...和self.shape = ...。
答案 1 :(得分：2)
我个人更喜欢单身人士的以下模式：
+ (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等同于[SomeClass class]）
以上更简洁，我更喜欢将任何单例代码保留在init和alloc之外，因为我可以根据需要创建多个实例。例如，在单元测试中。
我个人认为你不必保护程序员不要创建多个实例。合同是明确的：sharedPoolManager返回单例实例。如果这是您想要/需要的那么就使用它。否则以通常的方式创建实例。