- (nullable NSDate *)dateFromString:(NSString *)string;
- (NSString *)stringFromDate:(NSDate *)date;
常見的日期格式
NSString * -> NSDate *
NSString *string = @"2015-11-20 09:10:05";
NSDateFormatter *fmt = [[NSDateFormatter alloc] init];
fmt.dateFormat = @"yyyy-MM-dd HH:mm:ss";
NSDate *date = [fmt dateFromString:string];
NSLog(@"%@", date);
NSString *string = @"11月-20號/2015年 09-10:05秒";
NSDateFormatter *fmt = [[NSDateFormatter alloc] init];
fmt.dateFormat = @"MM月-dd號/yyyy年 HH-mm:ss秒";
NSLog(@"%@", [fmt dateFromString:string]);
- Tue May 31 17:46:55 +0800 2011
NSString *string = @"Tue May 31 17:46:55 +0800 2011";
NSDateFormatter *fmt = [[NSDateFormatter alloc] init];
fmt.dateFormat = @"EEE MMM dd HH:mm:ss Z yyyy";
fmt.locale = [[NSLocale alloc] initWithLocaleIdentifier:@"en_US"];
NSLog(@"%@", [fmt dateFromString:string]);
NSString *string = @"1745645645645";
NSTimeInterval second = string.longLongValue / 1000.0;
NSDate *date = [NSDate dateWithTimeIntervalSince1970:second];
NSLog(@"%@", date);
NSCalendar的注意點
#define iOS(version) ([UIDevice currentDevice].systemVersion.doubleValue >= (version))
NSCalendar *calendar = nil;
if ([UIDevice currentDevice].systemVersion.doubleValue >= 8.0) {
calendar = [NSCalendar calendarWithIdentifier:NSCalendarIdentifierGregorian];
} else {
calendar = [NSCalendar currentCalendar];
}
NSCalendar *calendar = nil;
if ([NSCalendar respondsToSelector:@selector(calendarWithIdentifier:)]) {
calendar = [NSCalendar calendarWithIdentifier:NSCalendarIdentifierGregorian];
} else {
calendar = [NSCalendar currentCalendar];
}
NSDate * -> NSString *
NSDate *date = [NSDate date];
NSDateFormatter *fmt = [[NSDateFormatter alloc] init];
fmt.dateFormat = @"yyyy年MM月dd號 HH:mm:ss";
NSString *string = [fmt stringFromDate:date];
獲得日期元素
NSString *string = @"2015-11-20 09:10:05";
NSString *month = [string substringWithRange:NSMakeRange(5, 2)];
NSLog(@"%@", month);
NSString *string = @"2015-11-20 09:10:05";
NSDateFormatter *fmt = [[NSDateFormatter alloc] init];
fmt.dateFormat = @"yyyy-MM-dd HH:mm:ss";
NSDate *date = [fmt dateFromString:string];
NSCalendar *calendar = [NSCalendar currentCalendar];
NSInteger month = [calendar component:NSCalendarUnitMonth fromDate:date];
NSInteger hour = [calendar component:NSCalendarUnitHour fromDate:date];
NSInteger minute = [calendar component:NSCalendarUnitMinute fromDate:date];
NSLog(@"%zd %zd %zd", month, hour, minute);
NSString *string = @"2015-11-20 09:10:05";
NSDateFormatter *fmt = [[NSDateFormatter alloc] init];
fmt.dateFormat = @"yyyy-MM-dd HH:mm:ss";
NSDate *date = [fmt dateFromString:string];
NSCalendar *calendar = [NSCalendar currentCalendar];
NSCalendarUnit unit = NSCalendarUnitYear | NSCalendarUnitMonth | NSCalendarUnitDay | NSCalendarUnitHour | NSCalendarUnitMinute | NSCalendarUnitSecond;
NSDateComponents *cmps = [calendar components:unit fromDate:date];
NSLog(@"%@", cmps);
日期比較
NSString *createdAtString = @"2015-11-20 11:10:05";
NSDateFormatter *fmt = [[NSDateFormatter alloc] init];
fmt.dateFormat = @"yyyy-MM-dd HH:mm:ss";
NSDate *createdAtDate = [fmt dateFromString:createdAtString];
NSDate *nowDate = [NSDate date];
/**
NSComparisonResult的取值
NSOrderedAscending = -1L, // 升序, 越往右邊越大
NSOrderedSame, // 相等
NSOrderedDescending // 降序, 越往右邊越小
*/
NSComparisonResult result = [nowDate compare:createdAtDate];
if (result == NSOrderedAscending) {
NSLog(@"createdAtDate > nowDate");
} else if (result == NSOrderedDescending) {
NSLog(@"createdAtDate < nowDate");
} else {
NSLog(@"createdAtDate == nowDate");
}
NSString *createdAtString = @"2015-11-20 09:10:05";
NSDateFormatter *fmt = [[NSDateFormatter alloc] init];
fmt.dateFormat = @"yyyy-MM-dd HH:mm:ss";
NSDate *createdAtDate = [fmt dateFromString:createdAtString];
NSTimeInterval interval = [createdAtDate timeIntervalSinceNow];
NSLog(@"%f", interval);
NSDateFormatter *fmt = [[NSDateFormatter alloc] init];
fmt.dateFormat = @"yyyy-MM-dd HH:mm:ss";
NSString *createdAtString = @"2015-11-01 09:10:05";
NSDate *createdAtDate = [fmt dateFromString:createdAtString];
NSString *otherString = @"2015-10-31 08:56:45";
NSDate *otherDate = [fmt dateFromString:otherString];
NSCalendar *calendar = nil;
if ([NSCalendar respondsToSelector:@selector(calendarWithIdentifier:)]) {
calendar = [NSCalendar calendarWithIdentifier:NSCalendarIdentifierGregorian];
} else {
calendar = [NSCalendar currentCalendar];
}
NSCalendarUnit unit = NSCalendarUnitYear | NSCalendarUnitMonth | NSCalendarUnitDay | NSCalendarUnitHour | NSCalendarUnitMinute | NSCalendarUnitSecond;
NSDateComponents *cmps = [calendar components:unit fromDate:createdAtDate toDate:otherDate options:0];
NSLog(@"%@", cmps);
條件判斷的一些注意點
1.判斷一個數組中是否有具體內容
1> 正確
if (array.count) {
}
2> 錯誤
if (array) {
}
2.判斷一個字符串是否有具體內容
1> 正確
if (string.length) {
}
2> 錯誤
if (string) {
}