排序NSDictionary,降序.如何使用`compare:options:`选择器发送选项？

Question

我试图对NSDictionary进行排序.

从Apple文档 我看到你可以使用keysSortedByValueUsingSelector:

NSDictionary *dict = [NSDictionary dictionaryWithObjectsAndKeys:
    [NSNumber numberWithInt:63], @"Mathematics",
    [NSNumber numberWithInt:72], @"English",
    [NSNumber numberWithInt:55], @"History",
    [NSNumber numberWithInt:49], @"Geography",
    nil];

NSArray *sortedKeysArray = [dict keysSortedByValueUsingSelector:@selector(compare:)];

这使:

// sortedKeysArray contains: Geography, History, Mathematics, English

但我想要:

// sortedKeysArray contains: English, Mathematics, History, Geography

我已经读过你可以使用compare:options:,并且NSStringCompareOptions可以改变比较以便在另一个方向上进行比较.

但是我不明白你如何compare:options: 使用选择器中的选项发送.

我想做这样的事情:

NSArray *sortedKeysArray = [dict keysSortedByValueUsingSelector:@selector(compare:options:NSOrderDescending)];

我该如何切换比较的顺序？

相关:https: //discussions.apple.com/thread/3411089？start = 0&tstart = 0

Answer 1

选项1:使用比较器-compare:反向调用:(感谢Dan Shelly!)

NSArray *blockSortedKeys = [dict keysSortedByValueUsingComparator: ^(id obj1, id obj2) {
     // Switching the order of the operands reverses the sort direction
     return [objc2 compare:obj1];
}];

只需反转降序和升序返回语句,您应该得到您想要的.

选项2:反转您拥有的阵列:

请参阅如何在Objective-C中撤消NSArray？

Answer 2

我用 ：

    NSSortDescriptor *sortOrder = [NSSortDescriptor sortDescriptorWithKey:@"self" ascending:NO];
    self. sortedKeys = [[self.keyedInventoryItems allKeys] sortedArrayUsingDescriptors:[NSArray arrayWithObject:sortOrder]];