cool hit counter How to tell when an object is freed in iosARC_Intefrankly

How to tell when an object is freed in iosARC

First let's understand the NSHashTable

NSHashTable follows the example of NSSet (NSMutableSet), but offers more manipulation options than NSSet, especially in terms of support for weak reference relations, and NSHashTable is more flexible when it comes to object/memory handling. Compared to NSSet, NSHashTable has the following features.

  • NSSet (NSMutableSet) holds strong references to its elements, and these elements are used with hash values and the isEqual: method to do hash detection and determine if they are equal.
  • NSHashTable is mutable, it has no immutable version.
  • It can hold a weak reference to an element and can correctly remove the object after it has been destroyed. And that can't be done at NSSet.
  • Its members can be copied as they are added.
  • Its members can use pointers to identify equality and do hash detection.
  • It can contain arbitrary pointers, and its members are not restricted to objects. We can configure an NSHashTable instance to manipulate arbitrary pointers, not just objects.
- (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.
    [self testWeakMemory];

Adding the object to be observed to the HashTable

- (void)testWeakMemory {
    if (!_hashTablele) {
        _hashTablele = [NSHashTable weakObjectsHashTable];
    _obj = [[NSObject alloc] init];
    [_hashTablele addObject:_obj];
    NSLog(@"hashTablele: %@", _hashTablele);

The HashTable determines if the object exists, and if not it is freed

- (void)viewWillDisappear:(BOOL)animated
    [super viewWillDisappear:animated];
    self.obj = nil;
    if ([_hashTablele containsObject:_obj]) {
        NSLog(@"obj The object was not released");
        NSLog(@"obj  The object has been released");
     NSLog(@"hashTablele: %@", _hashTablele);

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