java - 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，最近我看到在引用这些变量时出现空值的情况。

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
    ...
}

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

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

我已经在其中一项 Activity 中初始化了变量:

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

1. 我怀疑垃圾收集器是在中间被 android 踢掉的。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. 如果不是，还有什么问题？

额外详细信息:我的应用配置为在启动时自动启动。我仅在低端处理器和应用程序在启动时自动触发时面临上述问题。

Answer 1

关于上述问题，请注意以下几点:

1. 垃圾收集器只删除未引用的对象。静态变量只有在运行时从 JVM 卸载时才会丢失它们的值。

2. 应用程序通过 Activity 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，并且此时应用程序尚未运行，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，容易经常责怪它们，但 JVM 足够强大。