使用NSSortDescriptor将空白字符串放在排序末尾的简单方法? [英] Easy way to put blank strings at end of sort using NSSortDescriptor?

问题描述

我正在使用NSSortDescriptor对NSDictionary个项目的NSArray进行排序.效果很好，正是我所需要的...除了我希望字典项的排序键具有空​​白值的项显示在排序列表的末尾.有没有一种方法可以轻松实现这一目标?还是我必须创建一些自定义排序功能?不，我不想只是将其设置为DESC顺序...我希望排序的结果看起来像是A，A，B，B，C，空白，空白.

I'm using NSSortDescriptor to sort an NSArray of NSDictionary items. Works great, just what I needed... except that I'd like for the dictionary items that have blank values for my sort key to show up at the end of the sorted list. Is there a way to easily accomplish this? Or will I have to create some custom sorting functions? And no, I don't want to just set it to DESC order... I'd like sorted results to look like A, A, B, B, C, blanks, blank.

推荐答案

在看到另一个使用自定义比较的示例后，想到了这一点.这是我最后得到的代码:

Figured this out after seeing another example using a custom comparison. Here is the code I ended up with:

@interface NSString (CustomStatusCompare)
- (NSComparisonResult)customStatusCompare:(NSString*)other;
@end

@implementation NSString (CustomStatusCompare)
- (NSComparisonResult)customStatusCompare:(NSString*)other {
    NSAssert([other isKindOfClass:[NSString class]], @"Must be a NSString");
    if ([self isEqual:other]) {
        return NSOrderedSame;
    }
    else if ([self length] > 0 && [other length] > 0) {
        return [self localizedCaseInsensitiveCompare:other];        
    }
    else if ([self length] > 0 && [other length] == 0) {
        return NSOrderedAscending;
    }
    else {
        return NSOrderedDescending;
    } 
}
@end



NSSortDescriptor *serviceTypeDescriptor =
[[NSSortDescriptor alloc] initWithKey:@"Service"
                             ascending:YES
                             selector:@selector(localizedCaseInsensitiveCompare:)];

NSSortDescriptor *locationDescriptor = 
[[NSSortDescriptor alloc] initWithKey:@"Location"
                             ascending:YES
                             selector:@selector(customStatusCompare:)];  //using custom comparison here!

NSArray *descriptors = [NSArray arrayWithObjects:locationDescriptor, nameDescriptor, nil];        
self.navArray = [self.navArray sortedArrayUsingDescriptors:descriptors];

因此，如果两个字符串都不为空，则比较器返回NSOrderedSame ...如果两个字符串均为非空，则调用常规比较函数...如果只有一个字符串为空，则它将反转该比较的常规顺序.瞧！

So the comparer returns NSOrderedSame if both strings are empty... calls the regular comparison function if both strings are non-empty... if only one string is empty, it reverses the normal order of that comparison. Voila!

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