Question

我有一个标签和两个箭头按钮。当我按下左箭头时，我希望显示当前比该日期少一天。当我按下右箭头时，应该添加一天。

目前这是我的代码。

- (IBAction)addDay:(id)sender {
    NSDateComponents *dayComponent = [[NSDateComponents alloc] init];
    dayComponent.day = 1;
    NSCalendar *theCalendar = [NSCalendar currentCalendar];
    NSString *dateNow = _lblDate.text;

    // Convert string to date object
    NSDateFormatter *dateFormat = [[NSDateFormatter alloc] init];
    [dateFormat setDateFormat:@"EE. d MMMM YYYY"];
    NSDate *date = [dateFormat dateFromString:dateNow];

    date = [theCalendar dateByAddingComponents:dayComponent toDate:date options:0];
    NSString *dateString = [dateFormat stringFromDate:date];
    _lblDate.text = dateString;

}

- (IBAction)deleteDay:(id)sender {

    NSDateComponents *dayComponent = [[NSDateComponents alloc] init];
    dayComponent.day = 1;
    NSCalendar *theCalendar = [NSCalendar currentCalendar];
    NSString *dateNow = _lblDate.text;

    // Convert string to date object
    NSDateFormatter *dateFormat = [[NSDateFormatter alloc] init];
    [dateFormat setDateFormat:@"EE. d MMMM YYYY"];
    NSDate *date = [dateFormat dateFromString:dateNow];

    date = [theCalendar dateByAddingComponents:dayComponent toDate:date options:0];
    NSString *dateString = [dateFormat stringFromDate:date];
    _lblDate.text = dateString;

}

但由于某种原因，日期是错误的。添加和删除日期时没有模式。

有人能帮助我吗？

亲切的问候

Answer 1

我不确定这是主要问题，但在- (IBAction)deleteDay:(id)sender中，dayComponent.day = 1;应为dayComponent.day = -1;。

Answer 2

我看到了两个问题。

实际上并没有减少一天（看起来像添加？）
不更新主线程上的UI。

尝试进行这些更改：

- (IBAction)deleteDay:(id)sender {

    NSDateComponents *dayComponent = [[NSDateComponents alloc] init];
    dayComponent.day = -1;
    /* snip */
}

和...

[_lblDate performSelectorOnMainThread:@selector(setText:) withObject:dateString waitUntilDone:NO];

Answer 3

您的添加代码是正确的。但是，依赖于字符串到日期的转换会产生问题。我建议你将NSDate对象作为实例变量，然后在下一天或前一天更新此实例变量。更新值后，您可以使用dateformatter从此日期检索字符串。现在，当您使用标签的文本生成日期时，会产生问题。这就是你如何做到的

// currentDate is my instance variable.
currentDate = [[NSDate date] retain];
NSDateFormatter *dateFormat = [[[NSDateFormatter alloc] init] autorelease];
[dateFormat setDateFormat:@"EE. d MMMM YYYY"];
dateLabel.text = [dateFormat stringFromDate:currentDate];

这就是你的下一个功能会如何看起来像

   (IBAction)nextDay:(id)sender {

       NSDateComponents *dayComponent = [[NSDateComponents alloc] init];
       dayComponent.day = 1;
       NSCalendar *theCalendar = [NSCalendar currentCalendar];

       NSDateFormatter *dateFormat = [[[NSDateFormatter alloc] init] autorelease];
       [dateFormat setDateFormat:@"EE. d MMMM YYYY"];

       currentDate = [[theCalendar dateByAddingComponents:dayComponent toDate:currentDate options:0] retain];
       NSString *dateString = [dateFormat stringFromDate:currentDate];
       dateLabel.text = dateString;
    }

这是前一天

enter code here

    (IBAction)previousDay:(id)sender {

        NSDateComponents *dayComponent = [[NSDateComponents alloc] init];
        dayComponent.day = -1;
        NSCalendar *theCalendar = [NSCalendar currentCalendar];

        NSDateFormatter *dateFormat = [[[NSDateFormatter alloc] init] autorelease];
        [dateFormat setDateFormat:@"EE. d MMMM YYYY"];

        currentDate = [[theCalendar dateByAddingComponents:dayComponent toDate:currentDate options:0] retain];
        NSString *dateString = [dateFormat stringFromDate:currentDate];
        dateLabel.text = dateString;
    }

Answer 4

要添加一天，您需要添加一天的TimeInterval，如下所示

NSDate *newDate1 = [date addTimeInterval:60*60*24];

要减去一天，请执行以下操作

NSDate *newDate2 = [date addTimeInterval:-60*60*24];

标签未使用正确的日期刷新

4 个答案: