android - onRestoreInstanceState 中的 NullPointerException

Question

下面的

SwiperActivity，从 ActionBarSherlock 4.0.2 库扩展 SherlockFragmentActivity。我只能在加载不同的应用程序负载，然后切换回来后，在 ICS 4.0.3 OTA 上的 Asus Eee Pad Transformer TF101 以及 ICS 4.0.4 OTA 上的 Galaxy Nexus 上得到这个。我不确定这是否明显是 ICS 4.0.3 错误(它似乎与此处的 ICS 源代码匹配http://grepcode.com/file/repository.grepcode.com/java/ext/com.google.android/android/4.0.3_r1/com/android/internal/policy/impl/PhoneWindow.java#PhoneWindow.getPanelState%28int%2Cboolean%29)。

我也在 ActionBarSherlock 4.0.0 和 4.0.1 上得到了这个。

我不会覆盖 onRestoreInstanceState 或任何实例或状态。

(我还记录了每个被覆盖的 Activity 方法的第一行，例如“SwiperAct.onCreate 0”，最后是“SwiperAct.onCreate 99”，以尝试查明是哪种方法导致了这种情况。)

04-16 14:30:57.710: D/dalvikvm(667): GC_CONCURRENT freed 2692K, 71% free 8750K/30023K, paused 2ms+4ms
04-16 14:30:58.140: D/dalvikvm(667): GC_CONCURRENT freed 120K, 69% free 9362K/30023K, paused 3ms+4ms
04-16 14:30:58.480: D/dalvikvm(667): GC_CONCURRENT freed 16K, 67% free 10207K/30023K, paused 4ms+5ms
04-16 14:31:00.700: D/dalvikvm(18313): Late-enabling CheckJNI
04-16 14:31:00.700: I/ActivityManager(557): Start proc com.company.appname for activity com.company.appname/.SwiperActivity: pid=18313 uid=10011 gids={3003, 1015}
04-16 14:31:00.720: D/WindowManager(557): readLidState, sw:1
04-16 14:31:00.720: D/WindowManager(557): adjustConfigurationLw, config:{1.0 0mcc0mnc (no locale) layoutdir=0 sw800dp w1280dp h752dp xlrg land ?uimode ?night finger qwerty/v/v -nav/v} mLidOpen:1 mHasDockFeature:true mHasHallSensorFeature:true config.hardKeyboardHidden:1
04-16 14:31:00.730: D/OpenGLRenderer(18274): Flushing caches (mode 1)
04-16 14:31:00.730: D/dalvikvm(18313): Debugger has detached; object registry had 1 entries
04-16 14:31:00.900: D/OpenGLRenderer(18274): Flushing caches (mode 0)
04-16 14:31:00.950: D/OpenGLRenderer(667): Flushing caches (mode 0)
04-16 14:31:00.970: E/SwiperAct.onCreate 0(18313): starting...
04-16 14:31:00.980: D/SwiperAct.onSingleUse 0(18313): starting...
04-16 14:31:01.050: D/SQLiteUtil(18313): create DatabaseOpenHelper instance
04-16 14:31:01.050: D/SQLiteUtil(18313): create DatabaseOpenHelper instance
04-16 14:31:01.080: V/SQLiteOpenHelper(18313): onOpen()
04-16 14:31:01.100: V/SQLiteOpenHelper(18313): onOpen()
04-16 14:31:01.100: D/SwiperAct.onSingleUse 99(18313): ending...
04-16 14:31:01.120: D/dalvikvm(18313): GC_CONCURRENT freed 209K, 5% free 6728K/7047K, paused 4ms+2ms
04-16 14:31:01.190: E/SwiperAct.onCreate 99(18313): ending...
04-16 14:31:01.200: D/AndroidRuntime(18313): Shutting down VM
04-16 14:31:01.200: W/dalvikvm(18313): threadid=1: thread exiting with uncaught exception (group=0x40a7b1f8)
04-16 14:31:01.200: E/AndroidRuntime(18313): FATAL EXCEPTION: main
04-16 14:31:01.200: E/AndroidRuntime(18313): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.company.appname/com.company.appname.SwiperActivity}: java.lang.NullPointerException
04-16 14:31:01.200: E/AndroidRuntime(18313):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1956)
04-16 14:31:01.200: E/AndroidRuntime(18313):    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1981)
04-16 14:31:01.200: E/AndroidRuntime(18313):    at android.app.ActivityThread.access$600(ActivityThread.java:123)
04-16 14:31:01.200: E/AndroidRuntime(18313):    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1147)
04-16 14:31:01.200: E/AndroidRuntime(18313):    at android.os.Handler.dispatchMessage(Handler.java:99)
04-16 14:31:01.200: E/AndroidRuntime(18313):    at android.os.Looper.loop(Looper.java:137)
04-16 14:31:01.200: E/AndroidRuntime(18313):    at android.app.ActivityThread.main(ActivityThread.java:4424)
04-16 14:31:01.200: E/AndroidRuntime(18313):    at java.lang.reflect.Method.invokeNative(Native Method)
04-16 14:31:01.200: E/AndroidRuntime(18313):    at java.lang.reflect.Method.invoke(Method.java:511)
04-16 14:31:01.200: E/AndroidRuntime(18313):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784)
04-16 14:31:01.200: E/AndroidRuntime(18313):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551)
04-16 14:31:01.200: E/AndroidRuntime(18313):    at dalvik.system.NativeStart.main(Native Method)
04-16 14:31:01.200: E/AndroidRuntime(18313): Caused by: java.lang.NullPointerException
04-16 14:31:01.200: E/AndroidRuntime(18313):    at com.android.internal.policy.impl.PhoneWindow$PanelFeatureState.onRestoreInstanceState(PhoneWindow.java:3341)
04-16 14:31:01.200: E/AndroidRuntime(18313):    at com.android.internal.policy.impl.PhoneWindow.restorePanelState(PhoneWindow.java:1663)
04-16 14:31:01.200: E/AndroidRuntime(18313):    at com.android.internal.policy.impl.PhoneWindow.restoreHierarchyState(PhoneWindow.java:1619)
04-16 14:31:01.200: E/AndroidRuntime(18313):    at android.app.Activity.onRestoreInstanceState(Activity.java:906)
04-16 14:31:01.200: E/AndroidRuntime(18313):    at android.app.Activity.performRestoreInstanceState(Activity.java:878)
04-16 14:31:01.200: E/AndroidRuntime(18313):    at android.app.Instrumentation.callActivityOnRestoreInstanceState(Instrumentation.java:1100)
04-16 14:31:01.200: E/AndroidRuntime(18313):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1934)
04-16 14:31:01.200: E/AndroidRuntime(18313):    ... 11 more
04-16 14:31:01.200: W/ActivityManager(557):   Force finishing activity com.company.appname/.SwiperActivity
04-16 14:31:01.500: D/dalvikvm(18313): GC_CONCURRENT freed 177K, 4% free 7027K/7303K, paused 1ms+3ms
04-16 14:31:01.610: D/dalvikvm(18313): GC_CONCURRENT freed 114K, 3% free 7455K/7623K, paused 6ms+3ms
04-16 14:31:01.740: D/dalvikvm(18313): GC_CONCURRENT freed 117K, 3% free 7900K/8071K, paused 3ms+3ms
04-16 14:31:01.750: D/WindowManager(557): readLidState, sw:1
04-16 14:31:01.750: D/WindowManager(557): adjustConfigurationLw, config:{1.0 0mcc0mnc (no locale) layoutdir=0 sw800dp w1280dp h752dp xlrg land ?uimode ?night finger qwerty/v/v -nav/v} mLidOpen:1 mHasDockFeature:true mHasHallSensorFeature:true config.hardKeyboardHidden:1
04-16 14:31:01.750: W/ActivityManager(557): Activity pause timeout for ActivityRecord{41568e50 com.company.appname/.SwiperActivity}

Answer 1

我不能泄露源代码，因为它是用于工作的 - 但是我已经重命名并将其删除。然而，在将其剥离到我怀疑导致错误的部分并启用导致错误的行之后，错误不再发生!

所以这个源代码只是给任何其他经历过这种情况的人提供线索，让他们知道去哪里找。此代码实际上不会触发错误。

onCreate 调用 showSingleUse，它生成一个 SingleUseFragment，它在 Activity 中调用 onSingleUse(因为它实现了一个名为 OnFragmentUtilityListener 的接口(interface))。 onSingleUse 然后调用一个 AsyncTask，它在其 onPreExecute 中执行 findViewById。

禁用 findViewById，并将其移至 onCreate，即可解决问题。

SwiperActivity.java:

import android.os.AsyncTask;
import android.os.Build;
import android.os.Bundle;
import android.support.v4.app.FragmentActivity;
import android.widget.TextView;
import com.actionbarsherlock.app.SherlockFragmentActivity;

public class SwiperActivity extends SherlockFragmentActivity implements OnFragmentUtilityListener {
TextView textviewLastUpdated; // this is how the NPE was fixed
ReloadTask reloadTask;
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);
    textviewLastUpdated = (TextView) findViewById(R.id.textviewLastUpdated); // this is how the NPE was fixed
    showSingleUse(this);
}
public static void showSingleUse(FragmentActivity activity) {
    try {
        if (activity.getSupportFragmentManager().findFragmentByTag("singleusefragment") == null) {
            activity.getSupportFragmentManager().beginTransaction().add(new SingleUseFragment(), "singleusefragment").commit();
        }
    } catch (IllegalStateException e) {}
}
@Override
public void onSingleUse() {
    startReloadTask();
}
private class ReloadTask extends AsyncTask<Void, Void, Void> {
    @Override
    protected void onPreExecute() {
        showLoading();
    }
    @Override
    protected Void doInBackground(Void... arg0) {
        return null;
    }
    @Override
    protected void onPostExecute(Void result) {
        hideLoading();
    }
}
public static boolean allowsExecutorChange() {
    return Build.VERSION.SDK_INT > 10;
}
void startReloadTask() {
    reloadTask = new ReloadTask();
    if (allowsExecutorChange()) {
        reloadTask.executeOnExecutor(AsyncTask.THREAD_POOL_EXECUTOR);
    } else {
        reloadTask.execute();
    }
}
void showLoading() {
    // this was causing the NPE!
    //TextView textviewLastUpdated = (TextView) findViewById(R.id.textviewLastUpdated);
    if (textviewLastUpdated!=null) textviewLastUpdated.setText("Loading...");
}
void hideLoading() {
    // this was causing the NPE!
    //TextView textviewLastUpdated = (TextView) findViewById(R.id.textviewLastUpdated);
    if (textviewLastUpdated!=null) textviewLastUpdated.setText("Loaded!");
}
@Override
public void onDismissedDialog(String tag, Object data) {}
@Override
public void onClickedPositiveDialog(String tag, Object data) {}

OnFragmentUtilityListener.java:

public interface OnFragmentUtilityListener {
public void onDismissedDialog(String tag, Object data);
public void onClickedPositiveDialog(String tag, Object data);
public void onSingleUse();
}

SingleUseFragment.java:

/** hack-ish way to detect rotation and not do it again */
public class SingleUseFragment extends Fragment {
boolean wasRotating = false;
@Override
public void onActivityCreated(Bundle state) {
    super.onActivityCreated(state);
    setRetainInstance(true);
}
static SingleUseFragment newInstance() {
        return new SingleUseFragment();
    }
@Override
public void onAttach(Activity activity) {
    super.onAttach(activity);
    if (!wasRotating) ((OnFragmentUtilityListener) activity).onSingleUse();
}
@Override
public void onSaveInstanceState(Bundle outState) {
    super.onSaveInstanceState(outState);
    wasRotating = true;
}
}