ios - NSMutableArray 没有将数据正确存储到循环中

Question

我尝试将一些 NSMutableDictionaries 存储到 NSMutableArray 中并抛出一个 for 循环:

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项目的确切数量，但只有一个值。

我的意思是:

在循环内(NSLog(@"%@",element);):

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

循环后(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，每次迭代都会分配一个新字典:

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:这假定您使用的是 ARC，否则您将向右、向左和向中间泄漏字典...