NSMutableDictionary会对key进行强引用,对value进行copy,key必须有copyWithZone方法。
NSMapTable可以灵活配置key和value的内存管理方法,
更多类型见NSPointerFunctionsOptions枚举值
[NSMutableDictionary dictionary]
等同于
[NSMapTable mapTableWithKeyOptions:NSPointerFunctionsCopyIn valueOptions:NSPointerFunctionsStrongMemory]
比较一下区别
NSMutableDictionary *aMapTable = [NSMutableDictionary dictionary];
{
NSObject *object = [[NSObject alloc] init];
NSURL *key = [NSURL URLWithString:@"urlkey"];
[aMapTable setObject:object forKey:key];
uintptr_t count1 = _objc_rootRetainCount(key);
uintptr_t count2 = _objc_rootRetainCount(object);
NSLog(@"key retainCount:%lu, value retainCount:%lu",count1, count2);
NSLog(@"NSMapTable:%@", aMapTable);
}
NSLog(@"NSMapTable:%@", aMapTable);
结果
key retainCount:1, value retainCount:2
NSMapTable:{
urlkey = "<NSObject: 0x600000af6f60>";
}
NSMapTable:{
urlkey = "<NSObject: 0x600000af6f60>";
}
key是copy的,value是强引用的,大括号作用域结束后,临时变量被释放,value引用计数减1。
NSMapTable *aMapTable = [NSMapTable mapTableWithKeyOptions:NSPointerFunctionsStrongMemory valueOptions:NSPointerFunctionsWeakMemory];
{
NSObject *object = [[NSObject alloc] init];
NSURL *key = [NSURL URLWithString:@"urlkey"];
[aMapTable setObject:object forKey:key];
uintptr_t count1 = _objcrootRetainCount(key);
uintptr_t count2 = _objc_rootRetainCount(object);
NSLog(@"key retainCount:%lu, value retainCount:%lu",count1, count2);
NSLog(@"NSMapTable:%@", aMapTable);
}
NSLog(@"NSMapTable:%@", aMapTable);
结果:
key retainCount:1, value retainCount:1
NSMapTable:NSMapTable {
[6] urlkey -> <NSObject: 0x600001d5c940>
}
NSMapTable:NSMapTable {
}
key是copy的,value是弱引用,大括号作用域结束后,临时变量被释放,值不再存在。
更多推荐
Map和Dictionary
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