内存释放目标c

Question

Point of my view, when we create object and then set it = nil, this object will be release. but I tried to insert a lot of data to NSMutableDictionary, and then i set NIL for each object. Memory still be there and did not decrease. Please see my code:

- (void)viewDidLoad {
    [super viewDidLoad];
     NSMutableDictionary*frameAnotationLeft=[[NSMutableDictionary alloc] init];;
    // Do any additional setup after loading the view, typically from a nib.

    NSMutableDictionary *  testDict = [[NSMutableDictionary alloc] init];
    frameAnotationLeft = [[NSMutableDictionary alloc] init];
    for ( int j=0; j<1000; j++) {
        for (int i= 0; i<5000; i++) {

            NSString* __weak test = @"dule.For the most part, Automatic Reference Counting lets you completely forget about memory management. The idea is to focus on high-level functionality instead of the underlying memory management. The only thing you need to worry about are retain cycles, which was covered in the Properties module.For the most part, Automatic Reference Counting lets you completely forget about memory management. The idea is to focus on high-level functionality instead of the underlying memory management. The only thing you need to worry about are retain cycles, which was covered in the Properties module.For the most part, Automatic Reference Counting lets you completely forget about memory management. The idea is to focus on high-level functionality instead of the underlying memory management. The only thing you need to worry about are retain cycles, which was covered in the Properties module.For the most part, Automatic Reference Counting lets you completely forget about memory management. The idea is to focus on high-level functionality instead of the underlying memory management. The only thing you need to worry about are retain cycles, which was covered in the Properties module.";
            NSMutableArray * arrayTest = [[NSMutableArray alloc] init];
            [arrayTest addObject:test];
            test = nil;
            [testDict setObject:arrayTest forKey:[NSString stringWithFormat:@"%d",i]];

            arrayTest = nil;
        }

        [frameAnotationLeft setObject:testDict forKey:[NSString stringWithFormat:@"%d",j]];

    }

    testDict = nil;

    // Begin to release memory
    for (NSString* key in frameAnotationLeft) {

        NSMutableDictionary *testDict2 = (NSMutableDictionary*)[frameAnotationLeft objectForKey:key];

        for (NSString* key2 in testDict2) {
        NSMutableArray * arrayTest = (NSMutableArray *)[testDict2 objectForKey:key2];
        NSString* test = [arrayTest objectAtIndex:0];
        [arrayTest removeAllObjects];
        test = nil;
        arrayTest = nil;
    }
    [testDict2 removeAllObjects];
    testDict2 = nil;
    }
    [frameAnotationLeft removeAllObjects];
    frameAnotationLeft = nil;

}

Memory when i run it is 218 mb. and it did not decrease. Someone can help me and give me solution? Thank so muuch

Answer 1

If you are using ARC, setting local variables to nil is unnecessary and will have no effect. Local variables are completely memory-managed for you. And setting a variable to nil does not , as you imagine, cause the memory itself to be cleared; it reduces the object's retain count, but that's all. If the object's retain count has fallen to zero, then the memory may be reclaimed at some future time, but you have no control over when that will happen. Thus, your nil setting does nothing whatever, because the same thing is being done for you by ARC anyway.

If you are concerned about accumulation of secondary autoreleased objects during a tight loop (as here), simply wrap the interior of the loop in an @autoreleasepool block.