如何正确释放没有句柄的分配对象答案

【问题标题】：How to properly release assigned object with no handle如何正确释放没有句柄的分配对象
【发布时间】：2010-09-09 00:57:18
【问题描述】：

Instruments 指出这是内存泄漏，但我不确定如何正确释放它，或者何时应该释放它。是否有更好的约定为仅在循环内需要的新对象分配属性？具体行是expense.addedDate = [NSDate new];。

- (void) addObjects:(NSString *)itemDescription withItemAmount:(NSString *)itemAmount {
// Add a new expense to the persistent store.
NSString *expenseDescription = itemDescription;
NSString *expenseAmount = itemAmount;
if (!expenseDescription.length || !expenseAmount.length) {
    UIAlertView *invalidEntry = [[[UIAlertView alloc] initWithTitle:@"Invalid Entry" 
                                                            message:@"You must include a description and cost." 
                                                           delegate:self 
                                                  cancelButtonTitle:@"OK" 
                                                  otherButtonTitles:nil] autorelease];
    [invalidEntry show];
} else {
    Expense *expense = (Expense *)[NSEntityDescription insertNewObjectForEntityForName:@"Expense"
                                                                inManagedObjectContext:self.managedObjectContext];
    expense.addedDate = [NSDate new];
    expense.itemDescription = expenseDescription;
    expense.cost = [NSNumber numberWithInt:[expenseAmount intValue]];

    NSError *error;
    if (![self.managedObjectContext save:&error]) {
        NSLog(@"Error %@", [error localizedDescription]);
        UIAlertView *errorSave = [[[UIAlertView alloc] initWithTitle:@"Unable to Save!" 
                                                            message:@"Money manager was not able to save this entry." 
                                                           delegate:self 
                                                  cancelButtonTitle:@"OK" 
                                                  otherButtonTitles:nil] autorelease];
        [errorSave show];
    } else {
        NSLog(@"Saved Expense to Database.");
    }
}
}

【问题讨论】：

标签： ios objective-c memory-management retain

【解决方案1】：

我认为您不想使用new 选择器，因为它不是自动释放的。如果你正在寻找一个默认的、当前的时间戳、自动释放的 NSDate 对象，你应该使用：

expense.addedDate = [NSDate date];

为了记录，

[NSObject new]

等价于

[[NSObject alloc] init]

Apple's docs on the new method

【讨论】：

【解决方案2】：

如果你声明“expense.addedDate”的属性来使用retain (@property(retain)) 你不应该像你一样分配日期，因为对象的retainCount 为2，稍后当它被释放时会导致一个内存泄漏。

使用自动释放对象或在分配后释放对象就足够了。

例如

expense.addedDate = [NSDate date];  // will return an autoreleased object

或

NSDate* dt = [NSDate new];
expense.addedDate = dt;
[dt release];

或第三种方式

NSDate* dt = [[NSDate new] autorelease];

【讨论】：

自动释放（所以 #1 或 #3）是首选。