我有一个使用 ICS 操作栏上的选项卡的应用程序，其中每个选项卡内部都有一个片段。在某些情况下，在我按下操作栏上的选项菜单上的按钮，然后旋转设备后，我会收到 NullPointerException。我可以使用相同的步骤可靠地重现它，但是在某些情况下（例如，如果我不按操作栏上的任何按钮）不会产生异常。该异常似乎没有引用我的代码中的任何行，并且在方向更改后重新创建活动期间发生。
这是一个例外：
09-18 20:56:22.357: E/AndroidRuntime(689): FATAL EXCEPTION: main
09-18 20:56:22.357: E/AndroidRuntime(689): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.andavapps.flightbot/com.andavapps.flightbot.FlightBotActivity}: java.lang.NullPointerException
09-18 20:56:22.357: E/AndroidRuntime(689): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1956)
09-18 20:56:22.357: E/AndroidRuntime(689): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1981)
09-18 20:56:22.357: E/AndroidRuntime(689): at android.app.ActivityThread.handleRelaunchActivity(ActivityThread.java:3351)
09-18 20:56:22.357: E/AndroidRuntime(689): at android.app.ActivityThread.access$700(ActivityThread.java:123)
09-18 20:56:22.357: E/AndroidRuntime(689): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1151)
09-18 20:56:22.357: E/AndroidRuntime(689): at android.os.Handler.dispatchMessage(Handler.java:99)
09-18 20:56:22.357: E/AndroidRuntime(689): at android.os.Looper.loop(Looper.java:137)
09-18 20:56:22.357: E/AndroidRuntime(689): at android.app.ActivityThread.main(ActivityThread.java:4424)
09-18 20:56:22.357: E/AndroidRuntime(689): at java.lang.reflect.Method.invokeNative(Native Method)
09-18 20:56:22.357: E/AndroidRuntime(689): at java.lang.reflect.Method.invoke(Method.java:511)
09-18 20:56:22.357: E/AndroidRuntime(689): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784)
09-18 20:56:22.357: E/AndroidRuntime(689): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551)
09-18 20:56:22.357: E/AndroidRuntime(689): at dalvik.system.NativeStart.main(Native Method)
09-18 20:56:22.357: E/AndroidRuntime(689): Caused by: java.lang.NullPointerException
09-18 20:56:22.357: E/AndroidRuntime(689): at android.app.FragmentManagerImpl.dispatchCreateOptionsMenu(FragmentManager.java:1831)
09-18 20:56:22.357: E/AndroidRuntime(689): at android.app.Activity.onCreatePanelMenu(Activity.java:2445)
09-18 20:56:22.357: E/AndroidRuntime(689): at com.android.internal.policy.impl.PhoneWindow.preparePanel(PhoneWindow.java:388)
09-18 20:56:22.357: E/AndroidRuntime(689): at com.android.internal.policy.impl.PhoneWindow.invalidatePanelMenu(PhoneWindow.java:739)
09-18 20:56:22.357: E/AndroidRuntime(689): at com.android.internal.policy.impl.PhoneWindow.restorePanelState(PhoneWindow.java:1664)
09-18 20:56:22.357: E/AndroidRuntime(689): at com.android.internal.policy.impl.PhoneWindow.restoreHierarchyState(PhoneWindow.java:1619)
09-18 20:56:22.357: E/AndroidRuntime(689): at android.app.Activity.onRestoreInstanceState(Activity.java:906)
09-18 20:56:22.357: E/AndroidRuntime(689): at android.app.Activity.performRestoreInstanceState(Activity.java:878)
09-18 20:56:22.357: E/AndroidRuntime(689): at android.app.Instrumentation.callActivityOnRestoreInstanceState(Instrumentation.java:1100)
09-18 20:56:22.357: E/AndroidRuntime(689): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1934)
09-18 20:56:22.357: E/AndroidRuntime(689): ... 12 more
这是我的活动代码（为了简单起见，删除了一些不相关的代码）
public class MyActivity extends Activity {
private class MyTabListener<C extends MyFragment> implements ActionBar.TabListener {
private Activity activity;
private MyFragment fragmentMain;
private MyFragment fragmentSide;
private Class<C> cls;
public MyTabListener(Activity a, Class<C> c) {
activity = a;
cls = c;
}
@Override
public void onTabReselected(Tab tab, FragmentTransaction ft) { }
@Override
public void onTabSelected(Tab tab, FragmentTransaction ft) {
if (sidebar) {
if (fragmentSide == null) {
fragmentSide = (MyFragment) Fragment.instantiate(activity, cls.getName());
ft.add(c.SIDE_FRAME, fragmentSide, fragmentSide.getViewTag());
} else
ft.attach(fragmentSide);
} else {
if (fragmentMain == null) {
fragmentMain = (MyFragment) Fragment.instantiate(activity, cls.getName());
ft.add(c.MAIN_FRAME, fragmentMain, fragmentMain.getViewTag());
} else
ft.attach(fragmentMain);
}
selected = tabs.indexOf(tab);
mainUp = false;
if (setUpComplete)
invalidateOptionsMenu();
}
@Override
public void onTabUnselected(Tab tab, FragmentTransaction ft) {
if (fragmentSide != null && !fragmentSide.isDetached())
ft.detach(fragmentSide);
if (fragmentMain != null && !fragmentMain.isDetached())
ft.detach(fragmentMain);
}
}
private class MyMainTabListener<C extends MyFragment> implements ActionBar.TabListener {
private Activity activity;
private MyFragment fragmentMain;
private Class<C> cls;
public MyMainTabListener(Activity a, Class<C> c) {
activity = a;
cls = c;
}
@Override
public void onTabReselected(Tab tab, FragmentTransaction ft) { }
@Override
public void onTabSelected(Tab tab, FragmentTransaction ft) {
if (fragmentMain == null) {
fragmentMain = (MyFragment) Fragment.instantiate(activity, cls.getName());
ft.add(c.MAIN_FRAME, fragmentMain, fragmentMain.getViewTag());
} else if (fragmentMain.isDetached())
ft.attach(fragmentMain);
mainUp = !sidebar;
if (setUpComplete)
invalidateOptionsMenu();
}
@Override
public void onTabUnselected(Tab tab, FragmentTransaction ft) {
if (!sidebar && fragmentMain != null && !fragmentMain.isDetached())
ft.detach(fragmentMain);
else if (sidebar && (fragmentMain == null || fragmentMain.isDetached())) {
if (fragmentMain == null) {
fragmentMain = (MyFragment) Fragment.instantiate(activity, cls.getName());
ft.add(c.MAIN_FRAME, fragmentMain, fragmentMain.getViewTag());
} else if (fragmentMain.isDetached())
ft.attach(fragmentMain);
}
}
}
private static final class c {
//A bunch of constants are defined here
}
private ArrayList<ActionBar.Tab> tabs = new ArrayList<ActionBar.Tab>();
private int side;
private int orient;
private int selected;
private boolean sidebar;
private boolean mainUp;
private boolean lock;
private boolean setUpComplete = false;
@Override
public void onCreate(Bundle inState) {
super.onCreate(inState);
setContentView(R.layout.main_rel);
orient = detectOrientation();
if (inState != null) {
selected = inState.getInt("selected", 1);
side = inState.getInt("side", c.LEFT_SIDE);
sidebar = inState.getBoolean("visible", true);
mainUp = inState.getBoolean("mainup", !sidebar);
lock = inState.getBoolean("lock", false);
} else {
selected = 1;
side = c.LEFT_SIDE;
sidebar = true;
mainUp = false;
lock = false;
}
ActionBar ab = getActionBar();
ab.setNavigationMode(ActionBar.NAVIGATION_MODE_TABS);
tabs.add(ab.newTab().setText(MainFragment.getTabText()).setTabListener(new MyMainTabListener<MainFragment>(this, MainFragment.class)));
tabs.add(ab.newTab().setText(OtherFragment.getTabText()).setTabListener(new MyTabListener<OtherFragment>(this, OtherFragment.class)));
tabs.add(ab.newTab().setText(AnotherFragment.getTabText()).setTabListener(new MyTabListener<AnotherFragment>(this, AnotherFragment.class)));
tabs.add(ab.newTab().setText(YetAnotherFragment.getTabText()).setTabListener(new MyTabListener<YetAnotherFragment>(this, YetAnotherFragment.class)));
}
@Override
protected void onStart() {
super.onStart();
if (!setUpComplete)
setUp();
}
@Override
protected void onResume() {
super.onResume();
if (!setUpComplete)
setUp();
}
@Override
protected void onPause() {
super.onPause();
}
@Override
protected void onStop() {
super.onStop();
}
@Override
protected void onDestroy() {
super.onDestroy();
}
@Override
public void onSaveInstanceState(Bundle outState) {
setUpComplete = false;
getActionBar().removeAllTabs();
super.onSaveInstanceState(outState);
outState.putInt("selected", selected);
outState.putInt("side", side);
outState.putBoolean("visible", sidebar);
outState.putBoolean("mainup", mainUp);
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
getMenuInflater().inflate(R.menu.menu, menu);
return true;
}
@Override
public boolean onPrepareOptionsMenu(Menu menu) {
menu.findItem(R.id.menu_showhide).setTitle(c.MENU_SHOW_TEXT[(sidebar ? 1 : 0)]).setIcon(c.MENU_SHOW_DRAW[(sidebar ? 1 : 0)][side][orient][(mainUp ? 0 : 1)]);
menu.findItem(R.id.menu_swapside).setTitle(c.MENU_SIDE_TEXT[side][orient]).setIcon(c.MENU_SIDE_DRAW[side][orient]);
menu.findItem(R.id.menu_lock).setTitle(c.MENU_LOCK_TEXT[(lock ? 1 : 0)]).setIcon(c.MENU_LOCK_DRAW[(lock ? 0 : 1)]);
if (!sidebar)
menu.findItem(R.id.menu_swapside).setVisible(false).setEnabled(false);
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
switch (item.getItemId()) {
case R.id.menu_swapside:
toggleSide();
return true;
case R.id.menu_showhide:
toggleVisibility();
return true;
case R.id.menu_lock:
toggleRotation();
return true;
default:
return super.onOptionsItemSelected(item);
}
}
private int detectOrientation() {
int o = getResources().getConfiguration().orientation;
int r = getWindowManager().getDefaultDisplay().getRotation();
if (o == Configuration.ORIENTATION_LANDSCAPE && (r == Surface.ROTATION_0 || r == Surface.ROTATION_90))
return c.LAND_ORIENT;
else if (o == Configuration.ORIENTATION_PORTRAIT && (r == Surface.ROTATION_90 || r == Surface.ROTATION_180))
return c.RPORT_ORIENT;
else if (o == Configuration.ORIENTATION_LANDSCAPE && (r == Surface.ROTATION_180 || r == Surface.ROTATION_270))
return c.RLAND_ORIENT;
else
return c.PORT_ORIENT;
}
private void toggleVisibility() {
sidebar = !sidebar;
mainUp = !sidebar;
invalidateOptionsMenu();
setUpTabs();
}
private void toggleSide() {
side = (side == c.RIGHT_SIDE ? c.LEFT_SIDE : c.RIGHT_SIDE);
invalidateOptionsMenu();
setUpSide();
}
private void toggleRotation() {
lock = !lock;
invalidateOptionsMenu();
setUpLock();
}
private void setUp() {
setUpTabs();
setUpSide();
setUpLock();
setUpComplete = true;
}
private void setUpTabs() {
ActionBar ab = getActionBar();
ab.removeAllTabs();
ab.addTab(tabs.get(0), sidebar || mainUp);
if (sidebar)
ab.removeTab(tabs.get(0));
for (int i = 1; i < tabs.size(); i ++)
ab.addTab(tabs.get(i), !mainUp && selected == i);
}
private void setUpSide() {
RelativeLayout.LayoutParams params = new RelativeLayout.LayoutParams(RelativeLayout.LayoutParams.MATCH_PARENT, RelativeLayout.LayoutParams.MATCH_PARENT);
params.addRule(c.SIDE_RULE[side][orient], c.SIDE_FRAME);
FrameLayout mf = (FrameLayout) findViewById(c.MAIN_FRAME);
mf.setLayoutParams(params);
params = new RelativeLayout.LayoutParams(c.LAYOUT_WIDTH[orient], c.LAYOUT_HEIGHT[orient]);
params.addRule(c.ALIGN_RULE[side][orient]);
FrameLayout sf = (FrameLayout) findViewById(c.SIDE_FRAME);
sf.setLayoutParams(params);
}
private void setUpLock() {
setRequestedOrientation((lock ? c.LOCK_ORIENT[orient] : ActivityInfo.SCREEN_ORIENTATION_UNSPECIFIED));
}
}
关于我的应用程序和解释事情的代码的一些注释：
- 该应用程序显示一个主片段和一个侧边栏片段
- 选项菜单包含三个按钮：一个用于将侧边栏从屏幕一侧切换到另一侧，一个用于隐藏侧边栏，一个用于锁定方向
- 主片段始终是选项卡列表中的第一个，并且始终是 MainFragment 类型
- 我在运行 ICS（Asus Trans Prime，4.0.4；HTC Vivid，4.0.3）和模拟器（ICS 4.0.3 和 JB 4.1）的两台设备上运行它。这只发生在 ICS 上。
异常按以下顺序发生：
- 启动应用程序
- 按下按钮隐藏侧边栏
- 旋转装置
如果在旋转设备之前发生任何其他事情，则不会发生异常。例如，如果侧边栏未隐藏，我不会得到异常。如果先旋转设备，则永远不会发生异常，因此即使隐藏侧边栏，再次旋转设备，我也不会收到异常。而且堆栈跟踪没有引用我的代码中的单个函数，所以我什至可以找到根本原因。
似乎这是 FragmentManager.java（android.app 包）中引发异常的函数：
1827 public boolean dispatchCreateOptionsMenu(Menu menu, MenuInflater inflater) {
1828 boolean show = false;
1829 ArrayList<Fragment> newMenus = null;
1830 if (mActive != null) {
1831 for (int i=0; i<mAdded.size(); i++) {
1832 Fragment f = mAdded.get(i);
1833 if (f != null && !f.mHidden && f.mHasMenu && f.mMenuVisible) {
1834 show = true;
1835 f.onCreateOptionsMenu(menu, inflater);
1836 if (newMenus == null) {
1837 newMenus = new ArrayList<Fragment>();
1838 }
1839 newMenus.add(f);
1840 }
1841 }
1842 }
1843
1844 if (mCreatedMenus != null) {
1845 for (int i=0; i<mCreatedMenus.size(); i++) {
1846 Fragment f = mCreatedMenus.get(i);
1847 if (newMenus == null || !newMenus.contains(f)) {
1848 f.onDestroyOptionsMenu();
1849 }
1850 }
1851 }
1852
1853 mCreatedMenus = newMenus;
1854
1855 return show;
1856 }
mAdded在尝试使用它之前没有空检查。JB 中的相同功能替换(mActive != null)为(mAdded != null). 但我不知道我可以为 ICS 做些什么来避免这种情况。
有人有什么想法吗？我已经搜索过 StackOverflow 寻找类似的问题，但到目前为止都是空的。谢谢！如果还有什么我需要发布的，请告诉我，我会添加它。