Facebook的SDK 3.0示例

Question

所以，我正在練習這個代碼，我從來不知道出了什麼問題。我跟着它在本教程中的確切說法https://developers.facebook.com/docs/tutorials/androidsdk/3.0/scrumptious/authenticate/

這裏是我的代碼：應用程序意外停止。請幫助

public class MainActivity extends FragmentActivity { 
private static final int SPLASH = 0; 
private static final int SELECTION = 1; 
private static final int SETTINGS = 2; 
private static final int FRAGMENT_COUNT = SETTINGS +1; 
private Fragment[] fragments = new Fragment[FRAGMENT_COUNT]; 
private MenuItem settings; 
@Override 
public void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    uiHelper = new UiLifecycleHelper(this, callback); 
    setContentView(R.layout.main); 

    FragmentManager fm = getSupportFragmentManager(); 
    fragments[SELECTION] = fm.findFragmentById(R.id.selectionFragment); 
    fragments[SETTINGS] = fm.findFragmentById(R.id.userSettingsFragment); 


    FragmentTransaction transaction = fm.beginTransaction(); 
    for(int i = 0; i < fragments.length; i++) { 
     transaction.hide(fragments[i]); 
    } 
    transaction.commit(); 
} 

private void showFragment(int fragmentIndex, boolean addToBackStack) { 
    FragmentManager fm = getSupportFragmentManager(); 
    FragmentTransaction transaction = fm.beginTransaction(); 
    for (int i = 0; i < fragments.length; i++) { 
     if (i == fragmentIndex) { 
      transaction.show(fragments[i]); 
     } else { 
      transaction.hide(fragments[i]); 
     } 
    } 
    if (addToBackStack) { 
     transaction.addToBackStack(null); 
    } 
    transaction.commit(); 
} 


private boolean isResumed = false; 
@Override 
public void onResume() { 
super.onResume(); 
uiHelper.onResume(); 
isResumed = true; 
    } 
@Override 
    public void onPause() { 
super.onPause(); 
uiHelper.onPause(); 
isResumed = false; 
    } 
    @Override 
    public void onActivityResult(int requestCode, int resultCode, Intent data) { 
super.onActivityResult(requestCode, resultCode, data); 
uiHelper.onActivityResult(requestCode, resultCode, data); 
    } 

    @Override 
    public void onDestroy() { 
super.onDestroy(); 
uiHelper.onDestroy(); 
} 

    @Override 
    protected void onSaveInstanceState(Bundle outState) { 
super.onSaveInstanceState(outState); 
uiHelper.onSaveInstanceState(outState); 
} 


private void onSessionStateChange(Session session, SessionState state, Exception exception) { 
// Only make changes if the activity is visible 
if (isResumed) { 
    FragmentManager manager = getSupportFragmentManager(); 
    // Get the number of entries in the back stack 
    int backStackSize = manager.getBackStackEntryCount(); 
    // Clear the back stack 
    for (int i = 0; i < backStackSize; i++) { 
     manager.popBackStack(); 
    } 
    if (state.isOpened()) { 
     // If the session state is open: 
     // Show the authenticated fragment 
     showFragment(SELECTION, false); 
    } else if (state.isClosed()) { 
     // If the session state is closed: 
     // Show the login fragment 
     showFragment(SPLASH, false); 
    } 
} 
} 
@Override 
protected void onResumeFragments() { 
super.onResumeFragments(); 
Session session = Session.getActiveSession(); 

if (session != null && session.isOpened()) { 
    // if the session is already open, 
    // try to show the selection fragment 
    showFragment(SELECTION, false); 
} else { 
    // otherwise present the splash screen 
    // and ask the person to login. 
    showFragment(SPLASH, false); 
} 
} 

    private UiLifecycleHelper uiHelper; 
    private Session.StatusCallback callback = 
new Session.StatusCallback() { 
@Override 
public void call(Session session, 
     SessionState state, Exception exception) { 
    onSessionStateChange(session, state, exception); 
} 
}; 

@Override 
public boolean onPrepareOptionsMenu(Menu menu) { 
// only add the menu when the selection fragment is showing 
if (fragments[SELECTION].isVisible()) { 
    if (menu.size() == 0) { 
     settings = menu.add(R.string.settings); 
    } 
    return true; 
} else { 
    menu.clear(); 
    settings = null; 
} 
return false; 
} 

@Override 
public boolean onOptionsItemSelected(MenuItem item) { 
if (item.equals(settings)) { 
    showFragment(SETTINGS, true); 
    return true; 
} 
return false; 
} 
} 


    05-21 05:46:22.031: D/dalvikvm(527): GC_EXTERNAL_ALLOC freed 89K, 52% free 2603K/5379K, external 1808K/2137K, paused 89ms 
    05-21 05:46:22.221: D/AndroidRuntime(527): Shutting down VM 
    05-21 05:46:22.221: W/dalvikvm(527): threadid=1: thread exiting with uncaught exception (group=0x40015560) 
    05-21 05:46:22.241: E/AndroidRuntime(527): FATAL EXCEPTION: main 
    05-21 05:46:22.241: E/AndroidRuntime(527): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.firstandroidapp/com.firstandroidapp.MainActivity}: java.lang.NullPointerException 
    05-21 05:46:22.241: E/AndroidRuntime(527): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1647) 
    05-21 05:46:22.241: E/AndroidRuntime(527): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1663) 
    05-21 05:46:22.241: E/AndroidRuntime(527): at android.app.ActivityThread.access$1500(ActivityThread.java:117) 
    05-21 05:46:22.241: E/AndroidRuntime(527): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:931) 
    05-21 05:46:22.241: E/AndroidRuntime(527): at android.os.Handler.dispatchMessage(Handler.java:99) 
    05-21 05:46:22.241: E/AndroidRuntime(527): at android.os.Looper.loop(Looper.java:123) 
    05-21 05:46:22.241: E/AndroidRuntime(527): at android.app.ActivityThread.main(ActivityThread.java:3683) 
    05-21 05:46:22.241: E/AndroidRuntime(527): at java.lang.reflect.Method.invokeNative(Native Method) 
    05-21 05:46:22.241: E/AndroidRuntime(527): at java.lang.reflect.Method.invoke(Method.java:507) 
    05-21 05:46:22.241: E/AndroidRuntime(527): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839) 
    05-21 05:46:22.241: E/AndroidRuntime(527): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597) 
    05-21 05:46:22.241: E/AndroidRuntime(527): at dalvik.system.NativeStart.main(Native Method) 
    05-21 05:46:22.241: E/AndroidRuntime(527): Caused by: java.lang.NullPointerException 
    05-21 05:46:22.241: E/AndroidRuntime(527): at android.support.v4.app.BackStackRecord.run(BackStackRecord.java:609) 
    05-21 05:46:22.241: E/AndroidRuntime(527): at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1431) 
    05-21 05:46:22.241: E/AndroidRuntime(527): at android.support.v4.app.FragmentActivity.onStart(FragmentActivity.java:523) 
    05-21 05:46:22.241: E/AndroidRuntime(527): at android.app.Instrumentation.callActivityOnStart(Instrumentation.java:1129) 
    05-21 05:46:22.241: E/AndroidRuntime(527): at android.app.Activity.performStart(Activity.java:3791) 
    05-21 05:46:22.241: E/AndroidRuntime(527): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1620) 
    05-21 05:46:22.241: E/AndroidRuntime(527):  ... 11 more 
    05-21 05:47:01.391: I/Process(527): Sending signal. PID: 527 SIG: 9 

Answer 1

我有同樣的問題。

我解決的方法是首先進行調試，看看我的任何碎片「SPLASH」或「SELECTION」是否爲空。

而且它們是空的。

的原因是因爲我在Fragments類我是進口「android.app.Fragment」當從堆棧溢出這兩個答案幫我解決我應該輸入「android.support.v4.app.Fragment」

我問題：

Android FragmentManager BackStackRecord.run throwing NullPointerException

findFragmentById return null