Question

以下是关于增加接口部分中NSMutableArray类型变量的d保留计数值的程序。

@property (nonatomic, retain) NSMutableArray *dataArray;

实施部分

NSLog(@"%d",[self.dataArray retainCount]);
self.dataArray = [[NSMutableArray alloc] init];
NSLog(@"%d",[self.dataArray retainCount]);

现在在第一行它的显示保留计数值是NSLog内部的O，但是当我们分配数组时，它将保留计数增加到2.我没有明白这一点，为什么保留计数增加到2而不是1。请帮我理解这一点。

Answer 1

这可能会有所帮助：

http://whentouseretaincount.com

简而言之，您永远不应该依赖保留计数返回的值。

Answer 2

只有在覆盖getter / setter方法时才应使用_object。 “_object =”只是分配，而“self.object =”则调用其setter方法。您必须使用_object来防止和使用setter方法管理保留计数。通过编写代码来检查区别：

@property (nonatomic, retain) NSMutableArray *arr;


//=============Accessing with _object==========
 NSLog(@"Retain Count before Allocation => %lu", (unsigned long)_arr.retainCount);

    _arr = [NSMutableArray arrayWithArray:@[@"arrobj1", @"arrObj3"]];
    NSLog(@"Retain Count before Allocation => %lu", (unsigned long)_arr.retainCount);



    _arr = [[NSMutableArray alloc] init];
    NSLog(@"Retain Count After alloc+init => %lu", (unsigned long)_arr.retainCount);
//============================================
Output is :
Retain Count before Allocation => 0
Retain Count before Allocation => 1
Retain Count After alloc+init => 1




###### And also with accessing objects with self.object#######
//=============Accessing with _object==========

    NSLog(@"Retain Count before Allocation => %lu", (unsigned long)self.arr.retainCount);

    self.arr = [NSMutableArray arrayWithArray:@[@"arrobj1", @"arrObj3"]];
    NSLog(@"Retain Count before Allocation => %lu", (unsigned long)self.arr.retainCount);



    self.arr = [[NSMutableArray alloc] init];
    NSLog(@"Retain Count After alloc+init => %lu", (unsigned long)self.arr.retainCount);


//============================================
Output is: 
Retain Count before Allocation => 0
Retain Count before Allocation => 2
Retain Count After alloc+init => 2

我希望这会对你有所帮助。

Answer 3

alloc init创建一个保留的实例+1。然后保留的属性在赋值+2上添加一个保留。要获得一个保留计数，a）使用ARC和一个强大的属性，它将为您插入一个版本b）创建一个未保留的实例：

self.dataArray = [NSMutableArray array];

或c）明确自动释放：

self.dataArray = [[[NSMutableArray alloc] init] autorelease];

Answer 4

由于属性的setter也被调用

self.dataArray = [[NSMutableArray alloc] init];

保留计数被推升至2。

你也可以试试这个

NSMutableArray   *temp=[[NSMutableArray alloc]init];
self.dataArray = temp;
[temp release];

释放呼吁临时平衡额外的保留。

如何在iOS中增加NSMutableArray类型变量的保留计数

4 个答案: