将对象设置为 nil 时不会调用 dealloc 方法

我有个问题。

我首先创建了一个扩展 NSObject 的对象，我提供了描述和 dealloc 方法的重写。这是我的 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，我首先创建了一个 NSMutableArray 来保存 Employee 对象的列表：

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];
}

最后我将员工设置为零

employees = nil;

我预计dealloc要调用每个 Employee 对象的方法，我会看到一些日志，例如：

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

但是，我没有看到任何日志，如果我在dealloc方法中，断点永远不会被命中。

有什么想法吗？

一些观察结果：

1. person = nil不会释放非 ARC 代码中的对象。它将在 ARC 代码中（至少如果它很强大的话）。

2. 在 ARC 中，本地对象超出范围时会自动为您释放。在非 ARC 中，超出范围的对象不会为您释放（如果您在其他地方没有对这些对象的其他引用，则最终会导致泄漏）。

3. 将项目添加到可变数组中会增加该项目的保留计数，因此即使您在非 ARC 代码中包含释放，该对象也不会被释放，直到保留计数降至零（通过不仅释放来实现）将 person 对象添加到数组后，还将它们从数组中删除。

因此，鉴于这是非 ARC 代码，它可能类似于：

- (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 代码中：

- (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
}