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[英]What happens exactly, when I set an property to nil in the dealloc method?
[英]dealloc method is not invoked when set an object to nil
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方法的覆盖。 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];
}
最后我把员工定为零
employees = nil;
我期望调用每个Employee对象的dealloc
方法,我会看到一些日志,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
方法上设置断点,则断点永远不会被命中。
有什么想法吗?
几点意见:
person = nil
不会在非ARC代码中释放对象。 它将在ARC代码中(至少如果它很强大)。
在ARC中,当本地对象超出范围时,它们将自动为您释放。 在非ARC中,不会为您释放超出范围的对象(如果您在其他地方没有其他对这些对象的引用,则最终会泄漏)。
将项添加到可变数组将增加项的保留计数,因此即使您在非ARC代码中包含一个版本,该对象也不会被释放,直到保留计数降至零(不仅仅通过释放来完成)将对象添加到数组后,也将对象从数组中删除。
因此,鉴于这是非ARC代码,它可能是这样的:
- (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
}
解放对象的正确方法就是这样做
[employees release];
将其设置为nil
将不会释放内存。
由于您被允许调用[super dealloc]
,我可以假设您没有使用自动引用计数 。 这意味着您需要显式地将您编写的每个alloc
与平衡release
调用配对。 对于你来说,当你使数组为零时,你基本上泄露了员工的所有内存。 您需要再次遍历数组以释放它们,或者更好,因为您正在学习... 尽快开始编写ARC代码。
值得注意的是,ARC是针对这种情况而创建的; 它对我们的大脑有意义,现在如果你使用最新的工具它可以成为现实。
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