將對象設置為nil時不調用dealloc方法

Question

我有個問題。

我首先創建了一個擴展NSObject的對象，我提供了描述和dealloc方法的覆蓋。 這是我的Employee.m文件：

@implementation Employee
.....

-(NSString *)description
{
    return [NSString stringWithFormat:@"Employ ID: %d has $%d value of assets", [self     employeeID], [self valueOfAssets]];
}

-(void)dealloc
{   
    NSLog(@"deallocating.. %@", self);
    [super dealloc];
}

在我的main.m中，我首先創建了一個NSMutableArray來保存Employee對象列表：

NSMutableArray *employees = [[NSMutableArray alloc] init];

for (int i =0; i< 10; i++)
{
    // Create an instance of Employee
    Employee *person = [[Employee alloc] init];

    // Give the instance varaible interesting values
    [person setEmployeeID:i];
    [employees addObject: person];
}

最后我把員工定為零

employees = nil;

我期望調用每個Employee對象的dealloc方法，我會看到一些日志，如：

deallocating.. Employ ID 0 has value.....
deallocating.. Employ ID 2 has value.....
....

但是，我沒有看到任何日志，如果我在dealloc方法上設置斷點，則斷點永遠不會被命中。

有什么想法嗎？

Answer 1

幾點意見：

1. person = nil不會在非ARC代碼中釋放對象。 它將在ARC代碼中（至少如果它很強大）。

2. 在ARC中，當本地對象超出范圍時，它們將自動為您釋放。 在非ARC中，不會為您釋放超出范圍的對象（如果您在其他地方沒有其他對這些對象的引用，則最終會泄漏）。

3. 將項添加到可變數組將增加項的保留計數，因此即使您在非ARC代碼中包含一個版本，該對象也不會被釋放，直到保留計數降至零（不僅僅通過釋放來完成）將對象添加到數組后，也將對象從數組中刪除。

因此，鑒於這是非ARC代碼，它可能是這樣的：

- (void)testInNonArcCode
{
    NSMutableArray *employees = [[NSMutableArray alloc] init]; // employees retain count = +1

    for (int i =0; i< 10; i++)
    {
        //create an instance of Employee
        Employee *person = [[Employee alloc] init]; // person retain count = +1

        //Give the instance varaible interesting values
        [person setEmployeeID:i];
        [employees addObject: person];  // person retain count = +2
        [person release];  // person retain count = +1 (YOU REALLY WANT TO DO THIS OR ELSE OR NON-ARC PROGRAM WILL LEAK)
        // person = nil;   // this does nothing, except clears the local var that's limited to the for loop scope ... it does nothing to reduce the retain count or improve memory management in non-ARC code, thus I have commented it out
    }

    // do whatever you want

    [employees removeAllObjects]; // this will remove all of the person objects and they will have their respective retain counts reduced to 0, and therefore the Employee objects will be released

    [employees release]; // employees array's own retain count reduced to zero (and will now be dealloced, itself)
}

在ARC代碼中：

- (void)testInArcCode
{
    NSMutableArray *employees = [[NSMutableArray alloc] init]; // employees retain count = +1

    for (int i =0; i< 10; i++)
    {
        //create an instance of Employee
        Employee *person = [[Employee alloc] init]; // person retain count = +1

        //Give the instance varaible interesting values
        [person setEmployeeID:i];
        [employees addObject: person];  // person retain count = +2

        // person = nil;      // this would reduce person retain count to +1 (but unnecessary in ARC because when person falls out of scope, it will have it's retain count automatically reduced)
    }

    // do whatever you want

    [employees removeAllObjects]; // this will remove all of the person objects and they will have their respective retain counts reduced to 0, and therefore will be released

    // [employees release]; // not permitted in ARC
    // employees = nil;     // this would effectively release employees, but again, not needed, because when it falls out of scope, it will be released anyway
}

Answer 2

解放對象的正確方法就是這樣做

[employees release];

將其設置為nil將不會釋放內存。

Answer 3

由於您被允許調用[super dealloc] ，我可以假設您沒有使用自動引用計數 。 這意味着您需要顯式地將您編寫的每個alloc與平衡release調用配對。 對於你來說，當你使數組為零時，你基本上泄露了員工的所有內存。 您需要再次遍歷數組以釋放它們，或者更好，因為您正在學習... 盡快開始編寫ARC代碼。

值得注意的是，ARC是針對這種情況而創建的; 它對我們的大腦有意義，現在如果你使用最新的工具它可以成為現實。