问题描述
我试图理解ARC的工作方式，据我所知，我应该在这里做错事。这是我正在使用的代码：
I'm trying to understand the way ARC works, and as far as I know, I should be doing something wrong here. This is the code I'm using:
接口：
@interface ViewController : UIViewController{
}
@property (strong, nonatomic) NSString * myString ;
@property (weak, nonatomic) NSString * myPointer ;
实施：
- (void)viewDidLoad{
[super viewDidLoad];
self.myString = @"Hello world!" ; // myString is strong
self.myPointer = self.myString ; // myPointer var is weak
[self performSelector:@selector(makeNilMyValue) withObject:nil afterDelay:1];
[self performSelector:@selector(printValues) withObject:nil afterDelay:2];
}
- (void) makeNilMyValue{
self.myString = nil ;
}
- (void) printValues{
NSLog(@"myString: %@", self.myString) ;
NSLog(@"myPointer: %@", self.myPointer) ;
}
执行此操作后，我得到：
After executing this, I get:
2012-02-26 11:40:41.652 test1[933:207] myString: (null)
2012-02-26 11:40:41.653 test1[933:207] myPointer: Hello world!
如果我没错，由于myPointer很弱，它不应该保留内容物体。所以，它应该显示为nil而不是Hello World！。
If I'm not wrong, due to myPointer is weak, it shouldn't retain the content of the object. So, it should show nil instead of "Hello World!".
我做错了什么？
根据Caleb的回答，我创建了另一个弱指针，请参阅下面的代码：
- (void)viewDidLoad{
[super viewDidLoad];
self.myString = @"Hello world!" ; // myString is strong
self.myPointer = self.myString ; // myPointer var is weak
self.myPointer2 = self.myString ; // myPointer2 var is weak
[self performSelector:@selector(makeNilMyValue) withObject:nil afterDelay:1];
[self performSelector:@selector(printValues) withObject:nil afterDelay:2];
}
- (void) makeNilMyValue{
self.myPointer2 = @"value changed!" ;
self.myString = nil ;
}
- (void) printValues{
NSLog(@"myString: %@", self.myString) ;
NSLog(@"myPointer: %@", self.myPointer) ;
}
重点是我仍然得到了我以前的答案：
The point is that I still got the same answer I used to have:
2012-02-26 12:08:13.426 test1[1333:207] myString: (null)
2012-02-26 12:08:13.427 test1[1333:207] myPointer: Hello world!
推荐答案
正如Caleb指出的那样，为此使用常量NSString示例不是一个好主意。
As Caleb pointed out, using a constant NSString for this example is not a good idea.
NSString * temp = @/ tmp / scratch;请注意，以这种方式创建字符串
常量时，应避免使用除7位
ASCII字符之外的任何内容。这样的对象是在编译时创建的，并且在程序执行期间存在
。编译器使这个对象
常量在每个模块的基础上是唯一的，并且它们永远不会被释放，
尽管你可以保留并释放它们，就像你做任何其他对象一样。你
也可以直接发送消息到一个字符串常量，因为你做任何
其他字符串：
NSString *temp = @"/tmp/scratch"; Note that, when creating a string constant in this fashion, you should avoid using anything but 7-bit ASCII characters. Such an object is created at compile time and exists throughout your program’s execution. The compiler makes such object constants unique on a per-module basis, and they’re never deallocated, though you can retain and release them as you do any other object. You can also send messages directly to a string constant as you do any other string:
BOOL相同= [@比较isEqualToString： myString];
BOOL same = [@"comparison" isEqualToString:myString];
解释了常量字符串永远不会消失。
The documentation explains that constant strings will never disappear.
尝试使用其他东西进行实验。我尝试了NSObject，它产生了预期的结果。
Try using something else for your experiment. I tried NSObject and it produced expected results.
接口：
@interface ViewController : UIViewController
@property (strong, nonatomic) NSObject * myString;
@property (weak, nonatomic) NSObject * myPointer;
@end
实施：
@implementation ViewController
@synthesize myString = _myString;
@synthesize myPointer = _myPointer;
- (void)viewDidLoad{
[super viewDidLoad];
self.myString = [[NSObject alloc] init];
self.myPointer = self.myString;
self.myString = nil;
NSLog(@"myString: %@", self.myString);
NSLog(@"myPointer: %@", self.myPointer);
}
- (BOOL)shouldAutorotateToInterfaceOrientation:(UIInterfaceOrientation)interfaceOrientation
{
return (interfaceOrientation != UIInterfaceOrientationPortraitUpsideDown);
}
@end
弱指针设置为零如文档中所述，当没有强大的内存指针时 - 或。
Weak pointers are set to nil when there are no strong pointers to the memory as explained in the documentation - Apple Developer or llvm.
这篇关于iOS ARC - 弱而强的属性的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！