Android 静态变量丢失

Question

我正在使用一个只有静态变量的类来存储所有常量和运行时属性。但是，最近我看到引用这些变量时的实例，结果为空。

以下是我的类定义：

public class PlayerProperties {

    // Runtime but constant properties
    public static int screenHeight;
    public static int screenWidth;
    public static String androidId;

    // Static properties

    // Urls
    public static final String baseUrl = "http://www.blynq.in/api/player/";

    public static final String registerUrlAppender = "activationKeyValid";
    public static final String schedulesUrlAppender = "getScreenData";
    public static final String updateUrlAppender = "updateAvailable";
    public static final String tokenRegisterUrl = "fcmRegister";
    public static final String mediaStatsUrl = "mediaStats";
    public static final String logsUrl = "logs";
    public static final String pingUrl = "ping";
    public static final String screenInfoUrl = "screenInfo";

    // Developer Keys
    public static final String youtubeDeveloperKey = "ABCDEFGH...";

    // Folder structure
    public static final String mediaFolder = "player/media";
    public static final String imagesFolder = "player/media/images";
    public static final String videosFolder = "player/media/videos";
    public static final String pdfFolder = "player/media/pdf";
    public static final String gifFolder = "player/media/gif";
    public static final String webFolder = "player/media/web";
    public static final String othersFolder = "player/media/others";
    public static final String logsFolder = "player/logs";

    public static final String defaultFolder = "player/default/";
    public static final String serFolder = "player/ser/";
    public static final String tempFolder = "player/temp/";

    // Shared Prefs Keys
    public static final String ANDROID_ID_KEY = "ANDROID_ID";
    public static final String MY_PREFERENCES_KEY = "MyPrefs";


    // General properties
    public static final String dateTimeFormatString = "ddMMyyyyHHmmss";
    public static final String dateFormatString = "yyyy-MM-dd";

    // Timeouts
    public static final int httpPollTimeout = 20000;                    // in millis
    public static final int pingPeriodicity = 30;                       // in secs
    public static final int updateCheckPeriodicity = 24;                // in hrs
    public static final int pushEnabledPollPeriodicity = 30;            // in secs
    public static final int pushDisabledPollPeriodicity = 30;           // in secs
    public static final int statsUploadPeriodicity = 60;                // in mins
    public static final int logsUploadPeriodicity = 24;                 // in hours
    public static final int cleanupPeriodicity = 24;                    // in hours
    public static final int registrationStatusRecheckPeriod = 20000;    // in millis
    public static final int tokenResendToServerPeriod = 20000;          // in millis

    // Others
    public static final int maxTextHeight = 50; // in dp
    ...
}

我没有存储任何引用实例化 PlayerProperties 类，因为其中包含的所有变量都是静态的。

当我使用 引用变量 androidId 时PlayerProperties.androidId，我有时会得到 null。

我已经在其中一项活动中初始化了变量：

PlayerProperties.androidId = sharedpreferences.getString(PlayerProperties.ANDROID_ID_KEY, String.valueOf(UUID.randomUUID()));

1. 我怀疑垃圾收集器在两者之​​间被 android 踢了。如果 gc 启动，它会关闭我所有运行时初始化的静态变量吗？

2. 静态变量存储在哪个内存段？

3. 如果没有，还有什么问题？

额外细节：我的应用程序配置为在启动时自动启动。我仅在使用低端处理器以及在启动时自动触发应用程序时才面临上述问题。

Answer 1

关于上述问题，请注意以下几点：

1. 垃圾收集器仅删除未引用的对象。静态变量只有在运行时从 JVM 中卸载时才会丢失其值。

2. 当应用程序通过活动启动时会发生初始化。如果有任何服务/广播接收器正在访问其他类中的方法并使用这些 id，并且应用程序此时尚未运行，则未初始化的值将被引用为默认值。如果是字符串 - 它为空。

3. 与低端处理器无关，很容易经常责怪它们，但 JVM 足够强大。