在Android的单身问题 [英] Problems with singleton in android

问题描述

我有一个Android应用程序，其中有几个活动。每个活动的下载XML / JSON提要，分析它，并推动了一个单通常作为一个ArrayList。

I have an android app, where there are couple of activities. Each of the activities download an xml/json feed, parse it and push that to a singleton usually as an arraylist.

通过各种活动去后然而，似乎单身正在死去，最早期的下载数组列表是空的现在。为什么会这样呢？是不是跨活动共享数据独居建议的做法？

However after going through various activities, It seems the singleton is dying and most of the earlier downloaded array lists are now empty. Why is it so? Isn't singleton a recommended practice for sharing data across activities?

推荐答案

请参阅的 Android的API常见问题解答，在这里你一定会找到你的问题的最合适的解决方案（你是否需要一个短版活还是长寿命的数据）。

Please see this thread of Android API FAQ, here you will surely find the most appropriate solution for your problem (whether you need a short-living or a long-life data).

单身用于短生命周期对象。

Singletons are used for short life-cycle objects.

修改：请记住，对于数据的广泛的量它始终是一个更好的主意，使用数据库/ structurated本地文件（尽管后者是消耗资源的读/写）。如果你是非常复杂的对象的工作，选择共享preferences 可能会导致一些头痛了。

Edit: Please keep in mind, that for extensive amount of data it is always a better idea to use databases / structurated local files (though the latter are resource-consuming to read/write). And if you are working with very complex object, choosing SharedPreferences might cause some headache too.

存储/从加载列表共享preferences的样本：

// the name with which to store the shared preference
public static final String PERSON_LIST = "my.personlist";

// a sample data structure that will be stored
public static final class Person
{
    private String name;
    private int age;

    public String toString() 
    {
        return name + "|" + age;
    }

    // splits the passed String parameter, and retrieves the members
    public static Person loadPersonFromString(final String personString)
    {
        final Person p = new Person();
        final String[] data = personString.split("|");
        p.name = data[0];
        p.age = Integer.parseInt(data[1]);
        return p;
    }
}

/**
 * Saves the current list of Persons in SharedPreferences 
 * @param persons: the list to save
 */
public void savePersonList(final ArrayList<Person> persons) 
{
    final SharedPreferences prefs = PreferenceManager.
        getDefaultSharedPreferences(getApplicationContext());
    final Editor editor = prefs.edit();
    final StringBuilder builder = new StringBuilder();
    for (final Person person : persons)
    {
        if (builder.length() > 0)
            builder.append("-Person-");
        builder.append(person.toString());
    }
    editor.putString(PERSON_LIST, builder.toString());
    editor.commit();
}

/**
 * Loads the list of Persons from SharedPreferences
 * @return the loaded list
 */
public ArrayList<Person> loadPersonList()
{
    final SharedPreferences prefs = PreferenceManager.
        getDefaultSharedPreferences(getApplicationContext());
    final ArrayList<Person> persons = new ArrayList<Menu.Person>();
    final String[] array = prefs.getString(PERSON_LIST, "").split("-Person-");
    for (final String personString : array) 
    {
        if (personString.length() > 0)
            persons.add(Person.loadPersonFromString(personString));
    }
    return persons;
}

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