由网友(有个鬼故事叫开学.)分享简介：这是一个很奇怪的问题。我的应用程序运行得很好，但不知何故，如果我离开我的手机一两个小时，而我的应用程序正在运行，我得到以下错误，当我回来稍后：This is a very weird problem. My app that runs just fine but somehow if I leave my phone...

这是一个很奇怪的问题。我的应用程序运行得很好，但不知何故，如果我离开我的手机一两个小时，而我的应用程序正在运行，我得到以下错误，当我回来稍后：

This is a very weird problem. My app that runs just fine but somehow if I leave my phone for an hour or two while my app is running, I get the following error when I come back to it later:

java.lang.NoClassDefFoundError: yoga.database.Manager
at
yoga.YogaActivity.openDatabase(YogaActivity.java:294)
at
yoga.YogaActivity.initData(YogaActivity.java:275)
at
yoga.YogaActivity.onCreate(YogaActivity.java:102)
at
android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1123)
at
android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2364)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2417)
at android.app.ActivityThread.access$2100(ActivityThread.java:116)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1794)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loop(Looper.java:123)
at android.app.ActivityThread.main(ActivityThread.java:4203)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:521)
at
com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:791)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:549)
at dalvik.system.NativeStart.main(Native Method)

我知道一个事实，我yoga.database.Manager类是在当应用程序被启动，但不知何故，这个类必须被卸载的系统为我留下的电话时加载。

I know for a fact that my yoga.database.Manager class was loaded at the time when the app was launched, but somehow the class must have been unloaded by the system as I left the phone.

难道Android的某些时期后自动卸载类？我该怎么办时，我的课被卸载？

Does Android unload classes automatically after certain periods? What can I do when my class gets unloaded?

以上错误导致我的应用程序崩溃，但我可以很容易地重新启动它，它运行得很好。

The above error causes my app to crash, but I can easily re-launch it and it runs just fine.

多发生在我运行的是Android 1.6的HTC Magic手机中的问题。

The problem occurs mostly on my HTC Magic phone running Android 1.6.

推荐答案

Dalvik虚拟机目前不卸载类。如果有，那就只能这样做，当与一个特定的类加载器相关联的所有类可以同时被卸载，而你的应用程序正在运行，这将不会是这样的。

The Dalvik VM doesn't currently unload classes. If it did, it would only be able to do so when all classes associated with a particular class loader could be unloaded at once, which will not be the case while your app is running.

您需要检查的logcat输出的错误导致这一例外。得到的NoClassDefFoundError的一种方法是为某物的类有关的初始化过程中失败;如果发生有可能会是在日志中的痕迹。

You need to check the logcat output for errors leading up to this exception. One way to get a NoClassDefFoundError is for something to fail during initialization of the class in question; if that happened there would likely be a trail in the log.

（当然，这时的logcat输出可能早已不复存在，但如果问题是重复的，你会想在下一次捕捉到它。）

(Of course, by now the logcat output is probably long gone, but if the problem is repeatable you'll want to capture it next time.)