与Calendar.get（Calendar.HOUR）问题 [英] Problem with Calendar.get(Calendar.HOUR)

问题描述

我想在一个TextView显示时，我的应用程序上次更新（例如，上次在12:13更新）。我试图用一个日历实例，我想我理解正确的话，但我似乎遇到了麻烦我知道得到我使用的方法Calendar.getInstance（实例）。然后让我用Calendar.get（Calendar.HOUR）和Calendar.get（Calendar.MINUTE）小时和分钟。我的minute字段回报正确，但Calendar.HOUR是在24小时时钟返回小时，我想12小时制。我认为HOUR_OF_DAY为24小时制。我在哪里去了？

I am trying to display in a TextView when my application last updated (e.g., "Last updated at 12:13). I am trying to use a Calendar instance and I thought I understood it correctly but I seem to be having trouble. I know to get an instance I use the method Calendar.getInstance(). And then to get the hour and minute I was using Calendar.get(Calendar.HOUR) and Calendar.get(Calendar.MINUTE). My minute field returns correctly but Calendar.HOUR is returning the hour on a 24 hour clock and I want a 12 hour clock. I thought HOUR_OF_DAY was 24 hour clock. Where am I going wrong?

下面是code我使用的是：

Here is the code I'm using:

Calendar rightNow = Calendar.getInstance();
mTv.setText("Refreshed! Last updated " + 
           rightNow.get(Calendar.HOUR) + ":" + 
           rightNow.get(Calendar.MINUTE) + ".");

MTV是我的TextView是我更新。感谢您的帮助。

mTv is my TextView that I'm updating. Thanks for any help.

此外，这将是理想的，如果我可以说，最后更新5分钟前。而不是在下午12时13分最后更新。但我不知道最好的方法有此更新每分钟不消耗资源或电池...？

Also, it would be ideal if I could say "Last updated 5 minutes ago." instead of "Last updated at 12:13pm". But I'm not sure the best way to have this update each minute without draining resources or the battery...?

推荐答案

我推荐使用SimpleDateFormat的结合Date类用于格式化时间：

I'd recommend using SimpleDateFormat in combination with the Date class for formatting the time:

Date now = new Date();
SimpleDateFormat sdf = new SimpleDateFormat("K:mm a");
String formattedTime = sdf.format(now);

简短说明它是如何工作的：
您创建一个的SimpleDateFormat对象，并传递一个字符串给它的construtor告诉它如何格式化获取传递给它的格式（）函数每次时间/日期对象。
有很多常量/字母从而重新present一个特殊的时刻物体（例如秒，一个AM / PM标记..看的类文档的完整列表）。

K：毫米是指上午11:42格式 - 一位或两位数字的小时（根据其价值）的12小时格式，总是两位数分钟（MM）和AM或PM（a）中，根据时间

"K:mm a" means a "11:42 AM" format - one or two digits for the hour (depending on its value) in a 12 hour format, always two digits for minutes (mm) and either AM or PM (a), depending on the time.

你这样做之后，只是传递一个Date对象格式（）函数，你会得到一个格式化字符串。请注意，只是日期持有一个时间单点，如果从不带参数的构造函数创建它（=新的Date（）），它使用当前时间。如果需要其他时间，你可以传递一个长期争论的米利斯，你可能会得到来自Calendar.getTimeInMillis（）。

After you did that, just pass a Date object to the format() function, and you'll get a formatted string. Note that a Date just holds one single point in time, if you create it from the constructor with no arguments ("= new Date()") it uses the current time. If you need another time, you can pass a long argument with the millis, you may get that from Calendar.getTimeInMillis().

由于实施更新XY分钟前功能的 - 是的，你不得不更新这每一分钟，你必须计算的更新和当前时间之间的差异。我会说这是不值得的，从电池和额外的工作角度。
如果应用程序使用标准短的更新周期（如沿着这些线路每隔一小时或财产以后），而不是全屏，用户在他的屏幕顶部/底部可见的时钟。如果他真的要查多久是自更新，他可以采取短期的外观和比较（大多只是数分钟或数小时/分钟）。恕我直言那没有inconvinience为用户，至少它不会对我来说。我只是比较没有想到这一点。但我倾向于杀死它浪费我的电池没有有用的应用程序的原因。

As of implementing the "updated XY minutes ago function" - yes you'd have to update this every minute and you have to calculate the difference between the update and the current time. I'd say it's not worth it from a battery and extra work perspective. If your app uses standard short update cycles (e.g. every hour or somthing along those lines) and is not fullscreen, the user has a visible clock on top/bottom of his screen. If he really wants to check how long it was since the update, he can take a short look and compare (mostly just minutes or hours/minutes). And IMHO thats no inconvinience for a user, at least it would not for me. I'd just compare without thinking about that. But I tend to kill apps which waste my battery for no useful reason.

另外请注意，不是每个人都使用12小时格式。要获得本地化的时间格式取决于用户的设置/国家使用DateFormat.getTimeInstance（）。这将返回一个日期格式，但是这就像SimpleDateFormat的，只是通过一次格式化（）。

Also note that not everybody uses a 12-hour format. To get a localized time format depending on users settings/country use DateFormat.getTimeInstance(). This returns a DateFormat, but this works like the SimpleDateFormat, just pass a time to format().

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