构建nspredicate时EXC_BAD_ACCESS [英] EXC_BAD_ACCESS when building nspredicate

问题描述

我正在计算生日和今天之间的月数。
使用该数字，我正在构建一个谓词来从核心数据中获取对象。
虽然正确计算月数（如日志所示），但在构建谓词时我得到一个EXC_BAD_ACCESS。

I am calculating the number of months between a birthdate and today. With that number, I am building a predicate to fetch objects from core data. Although the number of months is calculated correctly (as the log shows), I am getting a EXC_BAD_ACCESS when building the predicate.

这是我的代码：

    NSCalendar *gregorian = [[NSCalendar alloc]
                         initWithCalendarIdentifier:NSGregorianCalendar];

    NSUInteger unitFlags = NSMonthCalendarUnit;

    NSDateComponents *components = [gregorian components:unitFlags
                                            fromDate:birthdate
                                              toDate:today options:0];
    int months = [components month];
    NSLog(@"months: %ld", (long)months);
    NSPredicate *pred = [NSPredicate predicateWithFormat:@"(alter_min_monat > %@)", months];

为什么会发生这种情况？

Why is this happening?

推荐答案

问题是占位符。
％@ 不应与 int 一起使用，但使用 ％d 代替。

The issue is the placeholder. %@ shouldn't be used with an int, but with a %d instead.

所以这一行：

NSPredicate *pred = [NSPredicate predicateWithFormat:@"(alter_min_monat > %@)", months];

应该是：

NSPredicate *pred = [NSPredicate predicateWithFormat:@"(alter_min_monat > %d)", months];

其他相关信息：字符串编程指南：字符串格式说明符

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