现在您应该对这个查询的大部分感到熟悉，所以我们只关注条件逻辑。
Most aspects of this query should be familiar to you by now, so concentrate on the conditional logic.
如果曾经从事过objective - c开发，那么应当对这个技巧感到熟悉。
If you've ever done any Objective-C development, this technique should look familiar.
如果您阅读了本系列之前的文章，那么您将对此感到熟悉(参见参考资料)。
If you have read the previous articles in this series, then this will be familiar to you (see Resources).
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