ios - NSPredicate 与 NSDate 按天/月过滤但不是年

Question

我需要创建一个谓词，它需要使用属性 creationDate 过滤对象列表，这是一个 NSDate 对象。我想获取具有相同日期和月份但不同年份的对象列表。实际上，我想要过去今天(作为日/月)发生的对象。我怎样才能创建这个谓词？例如:今天是 2016 年 7 月 27 日，我想要创建日期为 7 月 27 日的所有对象。

Answer 1

首先，从日期中提取日和月...

NSDateComponents *components = [[NSCalendar currentCalendar] components:NSCalendarUnitDay | NSCalendarUnitMonth | NSCalendarUnitYear fromDate:date];
NSInteger day = [components day];
NSInteger month = [components month];

接下来，(一种方式)构建谓词...

[NSPredicate predicateWithBlock:^BOOL(id object, NSDictionary * bindings) {
    // object must be cast to the type of object in the list
    MyObject *myObject = (MyObject *)object;
    NSDate *creationDate = myObject.creationDate;

    // do whatever you want here, but this block must return a BOOL
}];

将这些想法放在一起......

- (NSPredicate *)predicateMatchingYearAndMonthInDate:(NSDate *)date {
    NSDateComponents *components = [[NSCalendar currentCalendar] components:NSCalendarUnitDay | NSCalendarUnitMonth | NSCalendarUnitYear fromDate:date];
    NSInteger day = [components day];
    NSInteger month = [components month];

    return [NSPredicate predicateWithBlock:^BOOL(id object, NSDictionary * bindings) {
        MyObject *myObject = (MyObject *)object;
        NSDate *creationDate = myObject.creationDate;
        NSDateComponents *creationComponents = [[NSCalendar currentCalendar] components:NSCalendarUnitDay | NSCalendarUnitMonth | NSCalendarUnitYear fromDate:creationDate];
        NSInteger creationDay = [creationComponents day];
        NSInteger creationMonth = [creationComponents month];
        return day == creationDay && month == creationMonth;
    }];
}

就是这样。使用一些 NSDate 构建谓词，您希望在数组中匹配日期和月份，然后在数组上运行该谓词 (filteredArrayUsingPredicate:)。

NSDate *today = [NSDate date];
NSPredicate *predicate = [self predicateMatchingYearAndMonthInDate:today];
NSArray *objectsCreatedToday = [myArray filteredArrayUsingPredicate:predicate];