NSSortDescriptor优先级

Question

我使用NSSortDescriptor使用firstName对联系人进行排序，但如果名字是nil，则排序错误。

如果我有：

  

联系人1：Firstname = BAAAA和LastName = XXXXXX

     

联系人2：Firstname = nil和LastName = AAAAAA

它会是这样的。

1- AAAAAAA

2- BAAAA XXXXXX

所以我需要知道是否存在一个在Firstname和LastName之间建立优先级的解决方案。

如果Firstname ==nil那么采用LastName

谢谢

Answer 1

NSSortDescriptor *descriptor1 = [[NSSortDescriptor alloc] initWithKey:@"lastName" ascending:YES];
NSSortDescriptor *descriptor2 = [[NSSortDescriptor alloc] initWithKey:@"firstName" ascending:YES];
NSArray *sorted = [contatcs sortedArrayUsingDescriptors:@[descriptor1, descriptor2]];

数组中描述符的顺序决定了优先级。对于核心数据查询，它将类似于

NSManagedObjectContext *moc = [self managedObjectContext];
NSEntityDescription *entityDescription = [NSEntityDescription entityForName:@"Contact" inManagedObjectContext:moc];
NSFetchRequest *request = [[NSFetchRequest alloc] init];
[request setEntity:entityDescription];

[request setSortDescriptors:@[descriptor1, descriptor2]];

NSError *error;
NSArray *array = [moc executeFetchRequest:request error:&error];
if (array == nil)
{
    // Deal with error...
}

Answer 2

您可以继承NSSortDescriptor并覆盖compareObject:toObject:方法：

- (NSComparisonResult)compareObject:(id)object1 toObject:(id)object2 {
    NSString *firstName1 = [object1 valueForKey:@"firstName"];
    NSString *lastName1 = [object1 valueForKey:@"lastName"];

    NSString *firstName2 = [object2 valueForKey:@"firstName"];
    NSString *lastName2 = [object2 valueForKey:@"lastName"];

    if(firstName1 == nil || firstName2 == nil) {
        return [lastName1 compare:lastName2];
    }

    return [firstName1 compare:firstName2];
}