我知道 Cocoa 中关于内存管理(保留计数、自动释放池等)的基本原则，但是一旦你通过简单的保留/释放，它就会变得更加困惑。我找不到合适的答案，因为大多数教程都涵盖了简单的场景。我想问一下如何编写代码和避免泄漏的最佳实践。

第一个问题 - 迭代和临时分配:

for (id object in objectArray) {    
     Model *currentItem = object;
    /* do something with currentItem */
    [currentItem release];
}

Model *model = [unarchiver decodeObjectForKey:@"ARCHIVED_MODEL_OBJECT"];
// it has to be here, because (I was told) unarchiver will return autorelease object    
[model retain]; 
label.text = model.data;

- (IBAction) loadXMLButtonClicked:(id) sender {
    objectArray = [self loadData]; // 1 - objectArray is instance var
    NSArray *objectArray = [self loadData]; // 2 - objectArray is local var

    // loadXMLButtonClicked is called on button click, here the method finishes
    // and control goes back to application, autorelease pool is cleaned?

    // case 1 - objectArray stays retained in instance variable? (because setter was used)
    // case 2 - objectArray is soon to be released, there were no retains? 
    // (ignore the fact that it's local var, just hypothetically)

}

- (NSArray *) loadData {
    NSArray *objectArray = [[NSArray alloc] init];
    // populate array here
    return [objectArray autorelease];
}

- (NSArray *) loadData {
(...)
NSXMLParser *parser = [[NSXMLParser alloc] initWithData:data];
ModelXMLParser *parserDelegate = [[ModelXMLParser alloc] init];
[parser setDelegate:parserDelegate];
[parser parse];

objectArray = [[parserDelegate objectArray] copy]; 
// is this ok? *i* don't need the parser object so I think I should get rid of it
// and copy the data. How this copy works, is it shallow (only new reference to array)
// or deep copy (objects allocated again as well)?
// how to do deep copy of NSArray?

[parserDelegate release];
[parser release];
}

@implementation ModelXMLParser

@synthesize objectArray; // array of objects
@synthesize currentObject; // temporary object
@synthesize currentChars; // temporary chars
@synthesize parseChars; // parse chars only when there's need, leave those /t/n etc

- parser didStartElement (...) {
    if ([elementName isEqualToString:@"objects"]) {
        objectArray = [[NSMutableArray alloc] init];
    }
    else if ([elementName isEqualToString:@"object"]) {
        currentObject = [[Model alloc] init];
    }
    else if ([elementName isEqualToString:@"name"]) {
        // do I have to init currentObject.name (NSString) here? I guess not
        [self setParseChars:YES]; // just set the flag to make parse control easier
    }
    else if ([elementName isEqualToString:@"number"]) {
        // int isn't object anyway, no init
        [self setParseChars:YES]; // just set the flag to make parse control easier
    }   
}

- parser foundCharacters (...) {
    if (parseChars) {
        currentChars = [[NSString alloc] initWithString:string];
        // why is currentChars retainCount = 2 here?
        // is it like currentChars = [NSString new] and then currentChars = string? (so retain once more)
        // is it good way to control parser? (please ignore the NSMutableString and appending example, try this one)
        // should I just do currentChars = string here?

        [currentChars autorelease]; // this is currently my solution, because there's no leak, but I feel it's incorrect
    }
}

-  parser didEndElement (...) {
    if ([elementName isEqualToString:@"object"]) {
        [objectArray addObject:[currentObject copy]]; // should I copy here or just addObject, it retains anyway?
        [currentObject release]; // I've initialized currentObject before, now I don't need it, so I guess retainCount goes to 0 here?
    }
    else if ([elementName isEqualToString:@"name"]) {
        currentObject.name = currentChars; // is this correct, or shoud I do [currentChars copy] as well?
        [self setParseChars:NO];
        [currentChars release]; // as before, initialized, now releasing, but is this really correct?
    }
    else if ([elementName isEqualToString:@"number"]) {
        currentObject.number = [currentChars intValue]; // is this correct, or shoud I do [currentChars copy] as well?
        [self setParseChars:NO];
        [currentChars release]; // as before, initialized, now releasing, but is this really correct?
    }   
}

- (void) dealloc {
    // I shouldn't release currentChars or currentObject, those (I suppose) should be freed after parsing done,
    // as a result of earlier releases?

    [objectArray release];
    [super dealloc];
}

@implementation Model

@synthesize name; // this is NSString
@synthesize number; // this is int

- (id) copyWithZone:(NSZone *) zone {
    Model *copy = [[[self class] allocWithZone:zone] init];
    copy.name = [self.name copy];
    copy.number = self.number;
    return copy;
}

- (void) dealloc {
    [name release];
    // I don't have to release int, right? it's not an object
    [super dealloc];
}

最佳答案

第一个问题 - 迭代和临时分配

您不应该在此处释放对象，因为您不是所有者。如果您是对象的所有者，您应该只释放它。见 Memory Management Guide for Cocoa .如果您调用名称以 init 开头的方法，您只是对象的所有者。 , new ，或包含 copy以其名义。

由于 for 循环不使用具有任何这些名称的方法，因此您不是所有者，因此您不得释放对象。这将导致在对象完成之前释放对象，这几乎肯定会导致内存损坏和崩溃。

第二个问题 - 即时保留:

你不需要立即调用保留，你只需要在自动释放池下一次清空之前调用它。这可能是在您的方法返回主事件循环后不久。由于您不知道这会在何时发生，您必须确保如果您希望能够在函数(在本例中为 loadXMLButtonClicked:)返回后访问该对象，那么您必须 retain在你回来之前。

自 decodeObjectForKey不以 init 开头或 new或包含 copy以它的名义，您不会成为所有者。调用 retain使您成为所有者。

第三个问题 - 自动释放和传递变量:

首先，用同名的局部变量隐藏类成员是不好的做法。其次，除非loadData被用作多用途实用程序函数(我猜它不是，因为它不带任何参数)，它应该只将结果直接分配给成员变量 objectArray .返回结果然后将调用函数分配给成员变量是毫无意义且容易出错的。

第三，您没有使用 objectArray属性 setter ——您只是直接分配给成员变量。如果要使用setter，必须明确说self.objectArray = ... (前面有 self.)。因此，objectArray永远不会保留，所以它会在下一次自动释放池清除时被释放，这不是你想要的。你必须在某个时候保留它，或者相反，只是不要在 loadData 结束时自动释放它。 ，并为其分配类成员变量 objectArray .

如果属性是用 retain 声明的属性，然后使用setter 会自动调用retain当你用它赋值时(它也会 release 旧值)。如果相反，该属性是用 copy 声明的属性，那么每次分配给它时都会复制该值，并且您将成为新对象的所有者。

第 4 个问题 - 解析器 xml 最佳实践:

您正在制作对象数组的浅拷贝。如果要进行深拷贝，可以使用 initWithArray:copyItems: 信息。

do i have to init currentObject.name (NSString) here? i guess not?

why is currentChars retainCount = 2 here?

this is currently my solution, because there's no leak, but i feel it's incorrect?

should I copy here or just addObject, it retains anyway?

关于iphone - Objective-C 内存管理、xml 解析器和其他重要示例，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/546588/