objective-c - 带有文件内容的数组 : results in crash

Question

我正在创建一个应用程序，但收到 EXC_BAD_ACCESS 错误。

---

代码

@interface DNProjectsCategory : DNCategory {
  NSArray *projects;
}

@property(nonatomic, retain) NSArray *projects;

@end

还有:

@implementation DNProjectsCategory
@synthesize projects;

// MEM

- (void)dealloc {
  [projects release];
  
  [super dealloc];
}

// INIT.
- (id)init {
  if (self = [super init]) {
    title = NSLocalizedString(@"PROJECTS", nil);
    isSubCategory = NO;
    
    // Initialize projects
    //!!LINE 32 IS HERE!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
    projects = [NSArray arrayWithContentsOfFile:DNPROJECTSFILE];
  }
  
  return self;
}

// CATEGORIES

- (NSArray *)subCategories {
  NSMutableArray *projectsArray = [[[NSMutableArray alloc] init] autorelease];
  
  for (NSDictionary *project in projects) {
    DNCategory *projectCategory = [[DNCategory alloc] initWithTitle:[project valueForKey:@"title"]
                                                      subCategories:nil
                                                      isSubCategory:YES];
    
    [projectsArray addObject:projectCategory];
    [projectCategory release];
  }
  
  return projectsArray;
}

---

DNPROJECTSFILE 的内容

参见http://gist.github.com/618628

---

控制台和仪器

这是控制台在运行时显示的内容(NSZombie 已启用):

run
[Switching to process 41257]
Running…
2010-10-09 23:32:36.899 Done[41257:a0f] *** -[CFString isKindOfClass:]: message sent to deallocated instance 0x1001caab0
sharedlibrary apply-load-rules all

以下是 Instruments 在 NSZombie 测试中的说法:

Zombie Messaged

An Objective-C message was sent to a deallocated object (zombie) at address: 0x10012af80.

 

Stack Trace

   0 CoreFoundation _CFRuntimeCreateInstance
   1 CoreFoundation __CFStringCreateImmutableFunnel3
   2 CoreFoundation CFStringCreateWithBytes
   3 CoreFoundation _uniqueStringForCharacters
   4 CoreFoundation getString
   5 CoreFoundation parseXMLElement
   6 CoreFoundation parseXMLElement
   7 CoreFoundation parseArrayTag
   8 CoreFoundation parseXMLElement
   9 CoreFoundation parsePListTag
  10 CoreFoundation parseXMLElement
  11 CoreFoundation _CFPropertyListCreateFromXMLStringError
  12 CoreFoundation _CFPropertyListCreateWithData
  13 CoreFoundation CFPropertyListCreateFromXMLData
  14 Foundation _NSParseObjectFromASCIIPropertyListOrSerialization
  15 Foundation +[NSArray(NSArray) newWithContentsOf:immutable:]
  16 Foundation +[NSArray(NSArray) arrayWithContentsOfFile:]
  17 Done -[DNProjectsCategory init] /Users/rsonic/Developer/Done/DNProjectsCategory.m:32
  18 Done -[DNBindingsController categories] /Users/rsonic/Developer/Done/DNBindingsController.m:18
  19 Foundation -[NSObject(NSKeyValueCoding) valueForKey:]
  20 Foundation -[NSObject(NSKeyValueCoding) valueForKeyPath:]
  21 AppKit -[NSBinder valueForBinding:resolveMarkersToPlaceholders:]
  22 AppKit -[NSArrayDetailBinder _refreshDetailContentInBackground:]
  23 AppKit -[NSObject(NSKeyValueBindingCreation) bind:toObject:withKeyPath:options:]
  24 AppKit -[NSIBObjectData nibInstantiateWithOwner:topLevelObjects:]
  25 AppKit loadNib
  26 AppKit +[NSBundle(NSNibLoading) _loadNibFile:nameTable:withZone:ownerBundle:]
  27 AppKit +[NSBundle(NSNibLoading) loadNibNamed:owner:]
  28 AppKit NSApplicationMain
  29 Done main /Users/rsonic/Developer/Done/main.m:13
  30 Done start

---

问题

我真的不知道如何修复这个双重发布。据我所知，除了 dealloc 之外，我不会在任何地方释放 projects 变量。有人可以帮我吗？谢谢。

Answer 1

您没有使用访问器，因此项目永远不会保留。您的 init 方法有两种选择:

projects = [[NSArray arrayWithContentsOfFile:DNPROJECTSFILE] retain];

或

self.projects = [NSArray arrayWithContentsOfFile:DNPROJECTSFILE];

---

@property(nonatomic, retain) NSArray *projects;

该属性“创建”两个方法，一个 getter - (NSArray *)projects 和一个(在您的情况下更重要)setter - (void)setProjects:(NSArray*)a ; 您在属性声明中编写的保留语句仅适用于 setter。如果直接使用 projects = foo; 设置变量，则不会使用 setter。
但是 self.projects = foo; 相当于 [self setProject:foo]，这是动态创建的 setter。
您的 setter 看起来与此类似:

- (void)setProjects:(NSArray*)anArray {
    [anArray retain];
    [projects release];
    projects = anArray;
}

因此，如果您使用 setter，您从 arrayWithContentsOfFile: 获得的自动释放的 NSArray 将被保留。
在 Objective C 中进行的每个非“alloc”、“copy”、“retain”或任何以 new 开头的调用都会返回一个自动释放的对象。如果您想稍后使用它们(即在离开创建它们的方法之后)，则必须保留它们。

也许您想再看一下 Apple Memory Managment Guide