如何在 SharedPreferences 中保存和检索日期

问题描述

我需要在 android 的 SharedPreferences 中保存一些日期并检索它.我正在使用 AlarmManager 构建提醒应用程序，我需要保存未来日期列表.它必须能够以毫秒为单位进行检索.首先，我想计算现在时间和未来时间之间的时间并存储在共享偏好中.但该方法不起作用，因为我需要将它用于 AlarmManager.

I need to save a few dates in SharedPreferences in android and retrieve it. I am building reminder app using AlarmManager and I need to save list of future dates. It must be able to retrieve as milliseconds. First I thought to calculate time between today now time and future time and store in shared preference. But that method is not working since I need to use it for AlarmManager.

推荐答案

要保存和加载准确的日期，可以使用 Date 的 long(数字)表示对象.

To save and load accurate date, you could use the long (number) representation of a Date object.

示例:

//getting the current time in milliseconds, and creating a Date object from it:
Date date = new Date(System.currentTimeMillis()); //or simply new Date();

//converting it back to a milliseconds representation:
long millis = date.getTime();

您可以使用它从 SharedPreferences 中保存或检索 Date/Time 数据，如下所示

You can use this to save or retrieve Date/Time data from SharedPreferences like this

保存:

SharedPreferences prefs = ...;
prefs.edit().putLong("time", date.getTime()).apply();

回读:

Date myDate = new Date(prefs.getLong("time", 0));

编辑

如果你想额外存储 TimeZone，你可以为此编写一些辅助方法，类似这样(我没有测试过它们，如果有问题，请随时更正):

If you want to store the TimeZone additionaly, you could write some helper method for that purpose, something like this (I have not tested them, feel free to correct it, if something is wrong):

public static Date getDate(final SharedPreferences prefs, final String key, final Date defValue) {
    if (!prefs.contains(key + "_value") || !prefs.contains(key + "_zone")) {
        return defValue;
    }
    Calendar calendar = Calendar.getInstance();
    calendar.setTimeInMillis(prefs.getLong(key + "_value", 0));
    calendar.setTimeZone(TimeZone.getTimeZone(prefs.getString(key + "_zone", TimeZone.getDefault().getID())));
    return calendar.getTime();
}

public static void putDate(final SharedPreferences prefs, final String key, final Date date, final TimeZone zone) {
    prefs.edit().putLong(key + "_value", date.getTime()).apply();
    prefs.edit().putString(key + "_zone", zone.getID()).apply();
}

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