Question

无法理解为什么这不起作用，它只是说每次都没有使用过id num ......并且从不将它添加到数组中。任何有关这方面的帮助将非常感激。我几乎肯定错过了一些明显的东西，但它让我很生气。

- (IBAction)idNumInputEnd:(id)sender
{
    // Check if ID Number has been used before, if it hasnt, add it to the list.
    NSString *idNumCheck = idNumberInput.text;

    if ([idNumberList containsObject:idNumCheck])
    {
        NSLog(@"This id number has been used before, ask user if he would like to reload the       data");
    }
    else
    {
        NSLog(@"This id number hasn't been used before and is thus being added to the array");
        [idNumberList addObject:idNumCheck];
    }
}

Answer 1

我怀疑（由Martin分享，根据他的评论）idNumberList从未被分配并初始化为空NSMutableArray。

如果是这种情况，ARC会将nil分配给idNumberList，因此[idNumberList containsObject:idNumCheck]会评估为nil，以及[idNumberList addObject:idNumCheck]

换句话说，您评估的代码就像

if (nil) {
    NSLog(@"This id number has been used before, ask user if he would like to reload the       data");
} else {
    NSLog(@"This id number hasn't been used before and is thus being added to the array");
    nil;
}

鉴于此，将始终使用else分支，addObject对nil对象的调用将无声地失败，这会导致您遇到的行为。

要解决此问题，请按以下方式初始化idNumberList：

idNumberList = [[NSMutableArray alloc] init];

如果NSString尚未被提交，则将NSString添加到NSMutableArray - 不起作用

1 个答案: