Question

我正在尝试运行for循环并添加解析数据库中的所有对象以提供总计。这是我一直得到的错误：二进制表达式的操作数无效（'NSNumber *'和'NSNumber *'）

这是我的代码：

- (void)viewDidLoad
{
[super viewDidLoad];
PFQuery *query = [PFQuery queryWithClassName:@"Account"];
[query findObjectsInBackgroundWithBlock:^(NSArray *objects, NSError *error) {
    NSNumber *sum;
    for (PFObject *object in objects) {
        NSString *balanceString = object[@"startingBalance"];

        NSNumberFormatter *f = [[NSNumberFormatter alloc] init];
        [f setNumberStyle:NSNumberFormatterDecimalStyle];
        NSNumber *balanceNumber = [f numberFromString:balanceString];

        sum = sum + balanceNumber;
        NSLog(@"%f", sum);
    }


}];

Answer 1

您必须将NSNumber转换为基本类型（例如float或int）才能执行算术运算

float sum = 0;
NSNumberFormatter *f = [[NSNumberFormatter alloc] init]; // and you should reuse formatter
[f setNumberStyle:NSNumberFormatterDecimalStyle];
for (PFObject *object in objects) {
    NSString *balanceString = object[@"startingBalance"];
    NSNumber *balanceNumber = [f numberFromString:balanceString];

    sum += [balanceNumber floatValue];
    NSLog(@"%f", sum);
}

Answer 2

您不应对两个 nsnumber 对象执行算术运算，您应该将这些对象转换为float，long，double。执行算术运算后，您可以转换为 nsnumber 类型。

解析IOS的循环总和

2 个答案: