如何测试CoreData对象的属性是否为null？ [英] How can I test if an attribute of a CoreData object is null?

问题描述

我想测试是否已设置NSManageObject子类的NSNumber属性。请注意，该属性是NSNumber / Integer16
我尝试了几种方法，但没有奏效（以下情况始终为false）：

I want to test if an NSNumber attribute of a NSManageObject Subclass has been set or not. Note, that the attribute is of NSNumber / Integer16 I have tried several approaches but none worked (these below always evaluate to false):

// Note: patient.zyklus_laenge is of NSNumber (Integer16)
// does not work
id value = patient.zyklus_laenge;
if (value == [NSNull null]) {
    self.zyklusLaengeTextField.text = [NSString stringWithFormat:@"%d", 28];
} else {
    self.zyklusLaengeTextField.text = [NSString stringWithFormat:@"%@", patient.zyklus_laenge];
}
// does not work
if (!patient.zyklus_laenge) {
    self.zyklusLaengeTextField.text = [NSString stringWithFormat:@"%d", 28];
} else {
    self.zyklusLaengeTextField.text = [NSString stringWithFormat:@"%@", patient.zyklus_laenge];
}
// does not work
if ([patient.zyklus_laenge isEqual:nil]) {
    self.zyklusLaengeTextField.text = [NSString stringWithFormat:@"%d", 28];
} else {
    self.zyklusLaengeTextField.text = [NSString stringWithFormat:@"%@", patient.zyklus_laenge];
}
// does not work
if (patient.zyklus_laenge == nil) {
    self.zyklusLaengeTextField.text = [NSString stringWithFormat:@"%d", 28];
} else {
    self.zyklusLaengeTextField.text = [NSString stringWithFormat:@"%@", patient.zyklus_laenge];
}

有人能启发我并解释为什么这些都不起作用吗？

Can anyone enlighten me and explain me why these are not working?

推荐答案

id value = patient.zyklus_laenge;
if (value == [NSNull class]) 

to

id value = patient.zyklus_laenge;
if ([value isKindOfClass:[NSNull class]])

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