Question

我正在尝试创建一个标题不同的ActionBar。这取决于我的ListView中单击了哪一个。它给了我一个Nullpointerexception。

public class SuggestFrag extends Fragment implements View.OnClickListener {
Button suggestButton;
TextView title;
EditText suggestion;
Annonce annonce;

@Override
public View onCreateView(LayoutInflater i, ViewGroup container, Bundle savedInstanceState) {
    View rod = i.inflate(R.layout.frag_suggest, container, false);
    setHasOptionsMenu(true);
    getActivity().getActionBar().setTitle(annonce.getItemname()); //the errors occurs here


    suggestButton = (Button)rod.findViewById(R.id.suggestknap);
    suggestButton.setOnClickListener(this);

    suggestion = (EditText)rod.findViewById(R.id.suggestion);

    annonce = ((AnnonceDisplay)this.getActivity()).getAnnonce();

    return rod;
}

@Override
public void onClick(View view) {
    if(view == suggestButton) {
        AlertDialog alert = new AlertDialog.Builder(getActivity())
                .setMessage(suggestion.getText().toString())
                .setPositiveButton("Send", new DialogInterface.OnClickListener() {
                            @Override
                            public void onClick(DialogInterface dialog, int which) {
                                launchintent();

                            }
                        }
                )
                .setNegativeButton("Ændre", new DialogInterface.OnClickListener() {
                            @Override
                            public void onClick(DialogInterface dialog, int which) {
                                dialog.cancel();

                            }
                        }
                ).show();


    }
}

private void launchintent() {
    FragmentManager fm = getFragmentManager();
    Fragment f = fm.findFragmentById(R.id.fragment);
    if(fm.getBackStackEntryCount() > 0){
        fm.popBackStack();
    } else{
        getActivity().finish();
    }
}
@Override
public void onCreateOptionsMenu(Menu menu, MenuInflater inflater) {
    inflater.inflate(R.menu.menu_main, menu);
    super.onCreateOptionsMenu(menu, inflater);

}


@Override
public boolean onOptionsItemSelected(MenuItem item) {
    int id = item.getItemId();
    if (id == R.id.Forside) {
        Intent intent = new Intent(this.getActivity(), Forside.class);
        startActivity(intent);
    }
    else if (id == R.id.Logud){
        Intent intent = new Intent(this.getActivity(), LogInd.class);
        startActivity(intent);
    }

    return true;
 }
}

在我的活动中，它适用于汉堡包（或其他所谓的）。

编辑：

public class AnnonceDisplay extends Activity {

private Annonce annonce;
private Forslag forslag;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_annonce);

    annonce = (Annonce)getIntent().getExtras().getSerializable("annonce");

    if(savedInstanceState == null) {
        Fragment fragment = new AnnonceFrag();
        getFragmentManager().beginTransaction()
                .add(R.id.fragment, fragment)
                .commit();
    }
}

public Annonce getAnnonce() {
    return annonce;
}

public Forslag getForslag() { return forslag; }

public void setForlsag(Forslag forslag) {
    this.forslag = forslag;
 }

}

我在logcat中遇到的错误：

12-07 15:28:53.270 2056-2056/com.example.hadi.do2get E/AndroidRuntime: FATAL EXCEPTION: main
12-07 15:28:53.270 2056-2056/com.example.hadi.do2get E/AndroidRuntime: Process: com.example.hadi.do2get, PID: 2056
12-07 15:28:53.270 2056-2056/com.example.hadi.do2get E/AndroidRuntime: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.app.ActionBar.setTitle(java.lang.CharSequence)' on a null object reference
12-07 15:28:53.270 2056-2056/com.example.hadi.do2get E/AndroidRuntime:     at com.example.hadi.do2get.SuggestFrag.onCreateView(SuggestFrag.java:35)
12-07 15:28:53.270 2056-2056/com.example.hadi.do2get E/AndroidRuntime:     at android.app.Fragment.performCreateView(Fragment.java:2053)
12-07 15:28:53.270 2056-2056/com.example.hadi.do2get E/AndroidRuntime:     at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:894)
12-07 15:28:53.270 2056-2056/com.example.hadi.do2get E/AndroidRuntime:     at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:1067)
12-07 15:28:53.270 2056-2056/com.example.hadi.do2get E/AndroidRuntime:     at android.app.BackStackRecord.run(BackStackRecord.java:834)
 12-07 15:28:53.270 2056-2056/com.example.hadi.do2get E/AndroidRuntime:     at android.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1452)
 12-07 15:28:53.270 2056-2056/com.example.hadi.do2get E/AndroidRuntime:     at android.app.FragmentManagerImpl$1.run(FragmentManager.java:447)
 12-07 15:28:53.270 2056-2056/com.example.hadi.do2get E/AndroidRuntime:     at android.os.Handler.handleCallback(Handler.java:739)
 12-07 15:28:53.270 2056-2056/com.example.hadi.do2get E/AndroidRuntime:     at android.os.Handler.dispatchMessage(Handler.java:95)
 12-07 15:28:53.270 2056-2056/com.example.hadi.do2get E/AndroidRuntime:     at android.os.Looper.loop(Looper.java:135)
 12-07 15:28:53.270 2056-2056/com.example.hadi.do2get E/AndroidRuntime:     at android.app.ActivityThread.main(ActivityThread.java:5257)
 12-07 15:28:53.270 2056-2056/com.example.hadi.do2get E/AndroidRuntime:     at java.lang.reflect.Method.invoke(Native Method)
 12-07 15:28:53.270 2056-2056/com.example.hadi.do2get E/AndroidRuntime:     at java.lang.reflect.Method.invoke(Method.java:372)
 12-07 15:28:53.270 2056-2056/com.example.hadi.do2get E/AndroidRuntime:     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:903)
 12-07 15:28:53.270 2056-2056/com.example.hadi.do2get E/AndroidRuntime:     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698)

Answer 1

当然它将为null，因为annonce未初始化。首先初始化annonce，然后设置标题，如下所示：

@Override
public View onCreateView(LayoutInflater i, ViewGroup container, Bundle savedInstanceState) {
    View rod = i.inflate(R.layout.frag_suggest, container, false);
    setHasOptionsMenu(true);

    suggestButton = (Button)rod.findViewById(R.id.suggestknap);
    suggestButton.setOnClickListener(this);

    suggestion = (EditText)rod.findViewById(R.id.suggestion);
    //// Initialize first
    annonce = ((AnnonceDisplay)this.getActivity()).getAnnonce();
    //// Now set title
    getActivity().getActionBar().setTitle(annonce.getItemname()); 

    return rod;
}

Answer 2

将主题设置为清单文件中的活动

<activity android:name=".YourActivity"
              android:theme="@android:style/Theme.Holo.Light.DarkActionBar"/>

如果你使用来自支持librery的主题调用getSupportActionBar（）;

可以在片段类中创建带标题的ActionBar

2 个答案: