Question

我有一个NSString对象，我已经分配了。我想在应用程序的整个生命周期中偶尔附加到此字符串我对如何正确处理下面示例中的内存感到困惑。感谢。

我是否需要保留每次附加的字符串，或者可以使用属于自动释放池的字符串追加，stringByAppendingString:返回？
每次我做追加时，我是否泄漏了以前分配给my_string的内存？

代码：

NSString* my_string = [[NSString alloc] initWithString:@"Initial string"];
NSString* something = [NSString stringWithFormat:@"%@", @" with something"];
my_string = [[my_string stringByAppendingString:something] retain];
NSString* something_else = [NSString stringWithFormat:@"%@", @" and something_else"];
my_string = [[my_string stringByAppendingString:something_else] retain];
[my_string release];

Answer 1

NSString* my_string = [[NSString alloc] initWithString:@"Initial string"];

不是自动释放的（因为它是使用init ...方法创建的，这是一种约定），它的retainCount为1。

NSString* something = [NSString stringWithFormat:@"%@", @" with something"];

是自动释放的。

可以附加一个属于自动释放池的字符串，如 stringByAppendingString：返回

只要你期望它能存活下去。但是在你的代码中：

NSString* my_string = [[NSString alloc] initWithString:@"Initial string"];
NSString* something = [NSString stringWithFormat:@"%@", @" with something"];
my_string = [[my_string stringByAppendingString:something] retain];

你有泄漏。您应该在重新分配之前自动释放my_string。所以最后一行应该是：

my_string = [[[my_string autorelease] stringByAppendingString:something] retain];

否则你永远丢失了指向你想释放的对象的指针。当你保留结果时，你有责任释放它，所以你也应该在最后一行之前泄漏，这应该是

my_string = [[[my_string autorelease] stringByAppendingString:something_else] retain];

Answer 2

要记住的主要事情是NSString是不可变的。无论是分配，使用格式创建还是附加，您总是会返回 new 字符串对象。所以让我们打破这个：

NSString* my_string = [[NSString alloc] initWithString:@"Initial string"];
//String object created with "Initial string" content. Retain +1

NSString* something = [NSString stringWithFormat:@"%@", @" with something"];
//String object created with content " with something" and autoreleased.

my_string = [[my_string stringByAppendingString:something] retain];
//String object created with content "Initial string with something", autorelesed, and retained. Effective retain +1
//Assignment replaces old "Initial string" reference. "Initial string" object still has retain of +1, so it doesn't get deallocated (it leaks).

NSString* something_else = [NSString stringWithFormat:@"%@", @" and something_else"];
//String object created with content " and something_else" and autoreleased.

my_string = [[my_string stringByAppendingString:something_else] retain];
//String object created with contents "Initial string with something and something_else", autoreleaased, and retained. Effective retain +1
//Assignment replaces old "Initial string with something" reference. "initial string with something" object still had a retain of +1, so the object leaks.

[my_string release];
//String object "Initial string with something and something_else" released. Retain -1. Object is deallocated and doesn't leak.

//...Sometime later at the end of the runloop, the autorelease pool is drained and " with something" and " with something_else" are both deallocated.

所以：

是。可以附加一个自动释放的字符串。在运行循环结束之前，不会在自动释放的对象上调用release，这至少是在此方法退出之后。
是的，每次进行追加时，您都会泄漏先前分配给my_string的对象...但不是导致泄漏的追加，而是分配。您可以将nil分配给my_string，如果您先没有my_string或release，则用于指向的保留对象autorelease仍会泄漏。< / p>

Answer 3

在第二个作业中，您丢失了第一个stringByAppendingString来电的保留引用，因此：

可以在不调用retain的情况下附加字符串，除非您在代码中稍后需要该值。
是的，每次调用stringByAppendingString都会返回一个新的自动释放字符串。如果您暂时使用该值，请不要保留它。

附加到NSString时的适当内存管理

3 个答案: