ios - NSMutableArray 未将数据正确存储到循环中

Question

我尝试将一些存储NSMutableDictionaries到一个NSMutableArraythrow a for 循环中：

NSMutableArray *productsIdAndQuantities = [[NSMutableArray alloc]init];
NSMutableDictionary *element = [[NSMutableDictionary alloc]init];

for (id object in shoppingArray) {
    [element setObject:[object valueForKey:@"proId"] forKey:@"id"];
    [element setObject:[object valueForKey:@"qty"] forKey:@"quantity"];
    NSLog(@"%@",element);//tested, it's different on every iteration
    [productsIdAndQuantities addObject:element];
}

循环结束后，我尝试调试productsIdAndQuantities，结果发现它包含上面循环的确切数量的项目，但只有一个值。

这就是我的意思：

循环内部（NSLog(@"%@",element);）：

{
    id = 13293;
    quantity = "-2";
}
{
    id = 12632;
    quantity = "-5";
}

循环之后（NSLog(@"%@",productsIdAndQuantities);相同的值！！！！！！）：

(
    {
        id = 12632;
        quantity = "-5";
    },
    {
        id = 12632;
        quantity = "-5";
    }
)

Answer 1

您正在将相同的字典添加到数组中；改用它，它在每次迭代时分配一个新字典：

NSMutableArray *productsIdAndQuantities = [[NSMutableArray alloc]init];
for (id object in shoppingArray) {
    NSMutableDictionary *element = [[NSMutableDictionary alloc]init];
    [element setObject:[object valueForKey:@"proId"] forKey:@"id"];
    [element setObject:[object valueForKey:@"qty"] forKey:@"quantity"];
    NSLog(@"%@",element);//tested, it's different on every iteration
    [productsIdAndQuantities addObject:element];
}

注意：这假设您使用的是 ARC，否则您将在右侧、左侧和中心泄漏字典...