在NSArray上评估NSPredicate(不过滤) [英] Evaluating an NSPredicate on a NSArray (without filtering)

问题描述

是否可以在NSArray上评估NSPredicate，而不必让NSPredicate开始过滤掉数组中的对象?

Is it possible to evaluate a NSPredicate on a NSArray, without having the NSPredicate starting to filter out objects in the array?

例如，说我有以下谓词，它们仅检查数组中对象的数量:

For instance, say I have the following predicate that just checks the number of objects in an array:

NSPredicate *pred = [NSPredicate predicateWithFormat:@"count == 3"];
NSArray *list = [NSArray arrayWithObjects:@"uno", @"dos", @"volver", nil];
BOOL match = [pred evaluateWithObject:list];

这将崩溃，因为pred会尝试从数组中的第一个对象而不是数组本身中检索计数"键.

This will crash, as pred will try to retrieve the "count" key from the first object in the array instead of the array itself.

推荐答案

使用 NSPredicate 的 SIZE 运算符，它等同于 count 方法 NSArray .

Use the SIZE operator of NSPredicate which is equivalent to count method of NSArray.

NSPredicate *pred = [NSPredicate predicateWithFormat:@"SELF[SIZE] == 3"];
NSArray *list = [NSArray arrayWithObjects:@"uno", @"dos", @"volver", nil];
BOOL match = [pred evaluateWithObject:list];

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