iOS Objective-C: 获取指定年月的最后一天日期

您可以使用 NSCalendar 和 NSDateComponents 来实现这个功能。以下是一个示例代码：

- (NSInteger)getSelectedDayForYear:(NSInteger)year month:(NSInteger)month {
    NSCalendar *calendar = [NSCalendar currentCalendar];
    NSDateComponents *currentComponents = [calendar components:NSCalendarUnitYear | NSCalendarUnitMonth | NSCalendarUnitDay fromDate:[NSDate date]];
    NSDateComponents *selectedComponents = [[NSDateComponents alloc] init];
    selectedComponents.year = year;
    selectedComponents.month = month;
    selectedComponents.day = 1;
    NSDate *selectedDate = [calendar dateFromComponents:selectedComponents];
    
    if ([selectedDate compare:[NSDate date]] == NSOrderedDescending) {
        // 选中日期在当前日期之后
        return currentComponents.day;
    } else {
        NSRange range = [calendar rangeOfUnit:NSCalendarUnitDay inUnit:NSCalendarUnitMonth forDate:selectedDate];
        return range.length;
    }
}

使用示例：

NSInteger selectedDay = [self getSelectedDayForYear:2023 month:7];
NSLog('Selected day: %ld', (long)selectedDay);

上面的代码将根据传入的年和月返回选中的日期。如果选中日期在当前日期之后，将返回当前日期的天数。否则，将返回选中日期对应月份的天数。