[英]Releasing NSArray containing NSDictionary objects
I am having difficulty getting my head around memory management in the following segment of code on iPhone SDK 3.1. 在iPhone SDK 3.1的以下代码段中,我很难理解内存管理。
// Create array to hold each PersonClass object created below
NSMutableArray *arrayToReturn = [[[NSMutableArray alloc] init] autorelease];
NSArray *arrayOfDictionaries = [self generateDictionaryOfPeople];
[arrayOfDictionaries retain];
for (NSDictionary *dictionary in arrayOfDictionaries) {
PersonClass *aPerson = [[PersonClass alloc] init];
for (NSString *key in [dictionary keyEnumerator]) {
if ([key isEqualToString:[[NSString alloc] initWithString: @"FIRST_NAME"]])
aPerson.firstName = [dictionary objectForKey:key];
else if ([key isEqualToString:[[NSString alloc] initWithString: @"LAST_NAME"]])
aPerson.lastName = [dictionary objectForKey:key];
}
// Add the PersonClass object to the arrayToReturn array
[arrayToReturn addObject: aPerson];
// Release the PersonClass object
[aPerson release];
}
return arrayToReturn;
The [self generateDictionaryOfPeople]
method returns an array of NSDictionary objects. [self generateDictionaryOfPeople]
方法返回NSDictionary对象的数组。 Each NSDictionary object has two keys "FIRST_NAME" and "LAST_NAME" with a person's first name and last name as the respective data. 每个NSDictionary对象都有两个键“ FIRST_NAME”和“ LAST_NAME”,并以一个人的名字和姓氏作为各自的数据。 The code is looping through each dictionary object in the arrayOfDictionaries array and assigning the dictionary data to the relevant property of an aPerson (PersonClass) object.
代码遍历arrayOfDictionaries数组中的每个字典对象,并将字典数据分配给aPerson(PersonClass)对象的相关属性。 This object is then added to an array which is returned from this method.
然后将此对象添加到此方法返回的数组中。
When running instruments I am getting a leak for the dictionary objects contained in the arrayOfDictionaries array. 运行乐器时,我发现arrayOfDictionaries数组中包含的字典对象泄漏。 The code within the
[self generateDictionaryOfPeople]
method is calling [dictionaryObject release]
on each NSDictionary object as it is created and added to the array, which makes the retain count on the object 1 (as adding the object to the array would make the retain count 2, but then my release message decrements it back to 1). [self generateDictionaryOfPeople]
方法中的代码在创建每个NSDictionary对象并将其添加到数组时,在每个NSDictionary对象上调用[dictionaryObject release]
,这使对象1的保留计数(因为将对象添加到数组将使保留计数2,但随后我的发布消息将其递减回1)。
I assume this leak is because I am never releasing the arrayOfDictionaries array, and thus the NSDictionary objects within the array are never released. 我认为这种泄漏是因为我从未发布过arrayOfDictionaries数组,因此该数组内的NSDictionary对象也从未发布过。 If I attempt to release the array at the end of the above segment of code I get a "message sent to deallocated instance" error.
如果我尝试在上述代码段的末尾释放数组,则会收到“发送到已释放实例的消息”错误。 I understand why this is occurring, because I am assigning the aPerson object data within a dictionary item (that I am subsequently releasing) but I don't know where else I can release the arrayOfDictionaries array.
我知道为什么会这样,因为我正在将aPerson对象数据分配到词典项(随后要发布)中,但是我不知道还能在哪里发布arrayOfDictionaries数组。 Any help would be greatly appreciated.
任何帮助将不胜感激。
Thanks! 谢谢!
EDIT: Below is the implementation for [self generateDictionaryOfPeople]
编辑:以下是
[self generateDictionaryOfPeople]
- (NSArray *)generateDictionaryOfPeople {
NSMutableArray *arrayFromDatabase = [[[NSMutableArray alloc] init] autorelease];
// ** Query the database for data **
while ( there are rows being returned from the database ) {
// Declare an NSMutableDictionary object
NSMutableDictionary *dictionary = [[NSMutableDictionary alloc] init];
// Loop through each column for that row
for ( while there are columns for this row ) {
columnTitle = title_of_column_from_database
columnData = data_in_that_column_from_database
// Add to the dictionary object
[dictionary setObject:columnData forKey:columnTitle];
// Release objects
[columnName release];
[columnTitle release];
}
// Add the NSMutableDictionary object to the array
[arrayFromDatabase addObject:dictionary];
// Release objects
[dictionary release];
}
// Return the array
return arrayFromDatabase;
}
Here, 这里,
if ([key isEqualToString:[[NSString alloc] initWithString: @"FIRST_NAME"]])
aPerson.firstName = [dictionary objectForKey:key];
else if ([key isEqualToString:[[NSString alloc] initWithString: @"LAST_NAME"]])
aPerson.lastName = [dictionary objectForKey:key];
Replace them with 替换为
if ([key isEqualToString:@"FIRST_NAME"])
aPerson.firstName = [dictionary objectForKey:key];
else if ([key isEqualToString:@"LAST_NAME"])
aPerson.lastName = [dictionary objectForKey:key];
The problem of the leak is you're creating 1 ~ 2 NSString
-s per loop without -release
-ing them. 泄漏的问题是您在每个循环中创建
NSString
-s而不用-release
-ing它们。 If you need constant NSString
-s, just directly use them. 如果需要恒定的
NSString
-s,则直接使用它们。
I am still getting the original leak due to not releasing the arrayOfDictionaries array.
由于未释放arrayOfDictionaries数组,我仍然遇到原始泄漏。
That means you forgot to autorelease it in generateDictionaryOfPeople
. 这意味着您忘记了在
generateDictionaryOfPeople
自动释放它。
You need to review the memory management rules . 您需要查看内存管理规则 。
You are not releasing arrayFromDatabase
. 您没有释放
arrayFromDatabase
。 (The simplest way to avoid this kind of mistake is to use factories and autorelease
as early as possible rather than defer releases manually. In this case, use [NSMutableDictionary dictionary]
instead of [[NSMutableDictionary alloc] init]
.) (避免这种错误的最简单方法是尽早使用工厂和
autorelease
,而不是手动推迟释放。在这种情况下,请使用[NSMutableDictionary dictionary]
而不是[[NSMutableDictionary alloc] init]
。)
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