为什么点击主页按钮时我的活动崩溃？

Question

在这一点上，我很沮丧。我已经研究了几天，甚至无法隔离光标问题之外的任何内容。我正在扩展 ListActivity 并在 OnCreate 方法中使用 startManagingCursor(newcursor)。这是在点击主页按钮时运行并崩溃的代码（数据库已填满）：

private void loadAlbums() {
    try {
        newcursor = mDbHelper.getAlbumTitlesCursor();
        dbalbumadapter = new AlbumListCursorAdapter(this, newcursor);
        setListAdapter(dbalbumadapter);
        }
    catch (SQLiteException s) {
        newcursor = null;
        fetchalbums = new FetchAlbumsTask().execute();
        }
    current_view = ALBUMTITLE_VIEW;
}

这是错误日志：

02-03 13:41:42.379: WARN/dalvikvm(340): threadid=3: thread exiting with uncaught exception (group=0x4001b188)
02-03 13:41:42.389: ERROR/AndroidRuntime(340): Uncaught handler: thread main exiting due to uncaught exception

02-03 13:41:42.590: ERROR/AndroidRuntime(340): java.lang.RuntimeException: Unable to stop activity {com.skip.ngRCv2/com.skip.ngRCv2.ngRC}: java.lang.RuntimeException: Unable to stop activity {com.skip.ngRCv2/com.skip.ngRCv2.MusicLibraryActivity}: java.lang.NullPointerException
02-03 13:41:42.590: ERROR/AndroidRuntime(340):     at android.app.ActivityThread.performStopActivityInner(ActivityThread.java:3227)
02-03 13:41:42.590: ERROR/AndroidRuntime(340):     at android.app.ActivityThread.handleStopActivity(ActivityThread.java:3272)
02-03 13:41:42.590: ERROR/AndroidRuntime(340):     at android.app.ActivityThread.access$2500(ActivityThread.java:119)
02-03 13:41:42.590: ERROR/AndroidRuntime(340):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1880)
02-03 13:41:42.590: ERROR/AndroidRuntime(340):     at android.os.Handler.dispatchMessage(Handler.java:99)
02-03 13:41:42.590: ERROR/AndroidRuntime(340):     at android.os.Looper.loop(Looper.java:123)
02-03 13:41:42.590: ERROR/AndroidRuntime(340):     at android.app.ActivityThread.main(ActivityThread.java:4363)
02-03 13:41:42.590: ERROR/AndroidRuntime(340):     at java.lang.reflect.Method.invokeNative(Native Method)
02-03 13:41:42.590: ERROR/AndroidRuntime(340):     at java.lang.reflect.Method.invoke(Method.java:521)
02-03 13:41:42.590: ERROR/AndroidRuntime(340):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:860)
02-03 13:41:42.590: ERROR/AndroidRuntime(340):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:618)
02-03 13:41:42.590: ERROR/AndroidRuntime(340):     at dalvik.system.NativeStart.main(Native Method) 02-03 13:41:42.590: ERROR/AndroidRuntime(340): 
Caused by: java.lang.RuntimeException: Unable to stop activity {com.skip.ngRCv2/com.skip.ngRCv2.MusicLibraryActivity}: java.lang.NullPointerException
02-03 13:41:42.590: ERROR/AndroidRuntime(340):     at android.app.ActivityThread.performStopActivityInner(ActivityThread.java:3227)
02-03 13:41:42.590: ERROR/AndroidRuntime(340):     at android.app.ActivityThread.performStopActivity(ActivityThread.java:3174)
02-03 13:41:42.590: ERROR/AndroidRuntime(340):     at android.app.LocalActivityManager.moveToState(LocalActivityManager.java:176)
02-03 13:41:42.590: ERROR/AndroidRuntime(340):     at android.app.LocalActivityManager.dispatchStop(LocalActivityManager.java:572)
02-03 13:41:42.590: ERROR/AndroidRuntime(340):     at android.app.ActivityGroup.onStop(ActivityGroup.java:79)
02-03 13:41:42.590: ERROR/AndroidRuntime(340):     at android.app.Instrumentation.callActivityOnStop(Instrumentation.java:1169)
02-03 13:41:42.590: ERROR/AndroidRuntime(340):     at android.app.Activity.performStop(Activity.java:3797)
02-03 13:41:42.590: ERROR/AndroidRuntime(340):     at android.app.ActivityThread.performStopActivityInner(ActivityThread.java:3224)
02-03 13:41:42.590: ERROR/AndroidRuntime(340):     ... 11 more
02-03 13:41:42.590: ERROR/AndroidRuntime(340): 
Caused by: java.lang.NullPointerException
02-03 13:41:42.590: ERROR/AndroidRuntime(340):     at android.app.Activity.performStop(Activity.java:3808)
02-03 13:41:42.590: ERROR/AndroidRuntime(340):     at android.app.ActivityThread.performStopActivityInner(ActivityThread.java:3224)
02-03 13:41:42.590: ERROR/AndroidRuntime(340):     ... 18 more

在 Activity.performStop(Activity.java:3808) 处有一个 NullPointerException，它似乎来自 Activity.java 中的这个方法，即使我无法与行号交叉验证：

final void performStop() {
     if (!mStopped) {
         if (mWindow != null) {
             mWindow.closeAllPanels();
         }

         mCalled = false;
         mInstrumentation.callActivityOnStop(this);
         if (!mCalled) {
             throw new SuperNotCalledException(
                 "Activity " + mComponent.toShortString() +
                 " did not call through to super.onStop()");
         }

         synchronized (mManagedCursors) {
             final int N = mManagedCursors.size();
             for (int i=; i<N; i++) {
                 ManagedCursor mc = mManagedCursors.get(i);
                 if (!mc.mReleased) {
                     mc.mCursor.deactivate();
                     mc.mReleased = true;
                 }
             }
         }

         mStopped = true;
     }
     mResumed = false;
 }

我尝试在 OnStop 方法中关闭和停用光标，并将列表适配器设置为 null。我的印象是，当我指出让活动管理光标时，这些都不是必需的。我将光标传递给我的自定义适配器，但我发现的所有示例都没有在适配器内部进行任何管理。

如果您能帮助我至少缩小引发此异常的范围，我将不胜感激！

Answer 1

如果这是正确的版本，第 3808 行对应于：

[[我知道它不是官方的android源码，但是行号排成一行]]

http://code.google.com/p/pdn-slatedroid/source/browse/trunk/eclair/frameworks/base/core/java/android/app/Activity.java?r=12#3808

mc.mCursor.deactivate();

据我所知，mc 永远不能为空。 似乎 mCursor（这是最终的）只有在 null 光标被传递到 startManagingCursor() 时才能成为 null。其他人来确认这一点。

您能否在将光标传递到 startManagingCursor() 之前记录光标？ 我很好奇崩溃前该消息的最后一次出现是什么意思。

当出现 sql 异常时，你有这行：

newcursor = null;

我想知道 startManagingCursor() 通话中是否会出现这种情况。

---

注意事项：

• startManagingCursor() 创建一个ManagedCursor:

http://code.google.com/p/pdn-slatedroid/source/browse/trunk/eclair/frameworks/base/core/java/android/app/Activity.java?r=12#1549

public void startManagingCursor(Cursor c) {
    synchronized (mManagedCursors) {
        mManagedCursors.add(new ManagedCursor(c));
    }
}

• ManagedCursor 设置 final 字段 mCursor：

http://code.google.com/p/pdn-slatedroid/source/browse/trunk/eclair/frameworks/base/core/java/android/app/Activity.java?r=12#647

private static final class ManagedCursor {
    ManagedCursor(Cursor cursor) {
        mCursor = cursor;
        mReleased = false;
        mUpdated = false;
    }

    private final Cursor mCursor;
    private boolean mReleased;
    private boolean mUpdated;
}

• 对startManagingCursor() 的所有内部调用都受到保护，例如：

http://code.google.com/p/pdn-slatedroid/source/browse/trunk/eclair/frameworks/base/core/java/android/app/Activity.java?r=12#1465

if (c != null) {
    startManagingCursor(c);
}
return c;

Answer 2

在调试器中启动您的应用，在 NPE 上设置异常断点，然后查看它在哪里退出。

应该让你知道发生了什么。