Java 尝试创建抽屉时出现NullPointerException

嗨，伙计们，我在我的主要活动中遇到这个问题已经有一天了

at dalvik.system.NativeStart.main(Native Method)
Caused by: java.lang.NullPointerException
at 

但是我很确定我在试图找到正确片段的ID。但仍然不知道为什么会发生这种情况

这是我的密码：

com.serverus.flexibleui.MainActivity.onCreateMainActivity.java:43

MainActivity.java

package com.serverus.flexibleui;

import android.app.Fragment;
import android.app.FragmentManager;
import android.content.Intent;
import android.support.v4.widget.DrawerLayout;
import android.support.v7.app.ActionBarActivity;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.support.v7.widget.Toolbar;


public class MainActivity extends ActionBarActivity implements FragmentA.Communicator{

    FragmentA fragmentA;
    FragmentB fragmentB;
    FragmentManager manager;

    private Toolbar toolbar;

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

        manager = getFragmentManager();
        fragmentA = (FragmentA) manager.findFragmentById(R.id.fragment);
        // passing an object type MainActivity because main activity use the
        // Communicator Interface
        fragmentA.setCommunicator(this);

        toolbar= (Toolbar) findViewById(R.id.app_bar);

        setSupportActionBar(toolbar);
        getSupportActionBar().setDisplayShowHomeEnabled(true);

        DrawerLayout drawerLayout = (DrawerLayout) findViewById(R.id.drawer_layout);

        NavigationDrawerFragment drawerFragment = (NavigationDrawerFragment)
                getFragmentManager().findFragmentById(R.id.fragment_navigation_drawer);

        drawerFragment.setUp(drawerLayout, toolbar);
    }


    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.menu_main, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();

        //noinspection SimplifiableIfStatement
        if (id == R.id.action_settings) {
            return true;
        }

        return super.onOptionsItemSelected(item);
    }

    @Override
    public void respond(int positionIndex) {
        fragmentB = (FragmentB) manager.findFragmentById(R.id.fragment2);

        if(fragmentB != null && fragmentB.isVisible()){ //landscape orientation

            fragmentB.changeData(positionIndex);

        }else{ // portrait orietantion

            Intent intent = new Intent(this, AnotherActivity.class);
            intent.putExtra("positionIndex", positionIndex);
            startActivity(intent);

        }
    }
}

NavigationDrawerFragment.java

package com.serverus.flexibleui;

import android.app.Activity;
import android.net.Uri;
import android.os.Bundle;
import android.app.Fragment;
import android.support.v4.widget.DrawerLayout;
import android.support.v7.app.ActionBar;
import android.support.v7.app.ActionBarDrawerToggle;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.support.v7.widget.Toolbar;


/**
 * A simple {@link Fragment} subclass.
 * Activities that contain this fragment must implement the
 * {@link NavigationDrawerFragment.OnFragmentInteractionListener} interface
 * to handle interaction events.
 * Use the {@link NavigationDrawerFragment#newInstance} factory method to
 * create an instance of this fragment.
 */
public class NavigationDrawerFragment extends Fragment {
    // TODO: Rename parameter arguments, choose names that match
    // the fragment initialization parameters, e.g. ARG_ITEM_NUMBER
    private static final String ARG_PARAM1 = "param1";
    private static final String ARG_PARAM2 = "param2";

    // TODO: Rename and change types of parameters
    private String mParam1;
    private String mParam2;

    private OnFragmentInteractionListener mListener;

    private ActionBarDrawerToggle mDrawerToggle;
    private DrawerLayout mDrawerLayout;

    /**
     * Use this factory method to create a new instance of
     * this fragment using the provided parameters.
     *
     * @param param1 Parameter 1.
     * @param param2 Parameter 2.
     * @return A new instance of fragment NavigationDrawerFragment.
     */
    // TODO: Rename and change types and number of parameters
    public static NavigationDrawerFragment newInstance(String param1, String param2) {
        NavigationDrawerFragment fragment = new NavigationDrawerFragment();
        Bundle args = new Bundle();
        args.putString(ARG_PARAM1, param1);
        args.putString(ARG_PARAM2, param2);
        fragment.setArguments(args);
        return fragment;
    }

    public NavigationDrawerFragment() {
        // Required empty public constructor
    }

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        if (getArguments() != null) {
            mParam1 = getArguments().getString(ARG_PARAM1);
            mParam2 = getArguments().getString(ARG_PARAM2);
        }
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        // Inflate the layout for this fragment
        return inflater.inflate(R.layout.fragment_navigation_drawer, container, false);
    }

    // TODO: Rename method, update argument and hook method into UI event
    public void onButtonPressed(Uri uri) {
        if (mListener != null) {
            mListener.onFragmentInteraction(uri);
        }
    }

    @Override
    public void onAttach(Activity activity) {
        super.onAttach(activity);
        try {
            mListener = (OnFragmentInteractionListener) activity;
        } catch (ClassCastException e) {
            throw new ClassCastException(activity.toString()
                    + " must implement OnFragmentInteractionListener");
        }
    }

    @Override
    public void onDetach() {
        super.onDetach();
        mListener = null;
    }

    public void setUp(DrawerLayout drawerLayout, Toolbar toolbar) {
        mDrawerLayout = drawerLayout;
        mDrawerToggle = new ActionBarDrawerToggle(getActivity(), drawerLayout, toolbar, R.string.drawer_open, R.string.drawer_close){

            @Override
            public void onDrawerOpened(View drawerView) {
                super.onDrawerOpened(drawerView);
            }

            @Override
            public void onDrawerClosed(View drawerView) {
                super.onDrawerClosed(drawerView);
            }
        };


        mDrawerLayout.setDrawerListener(mDrawerToggle);


    }

    /**
     * This interface must be implemented by activities that contain this
     * fragment to allow an interaction in this fragment to be communicated
     * to the activity and potentially other fragments contained in that
     * activity.
     * <p/>
     * See the Android Training lesson <a href=
     * "http://developer.android.com/training/basics/fragments/communicating.html"
     * >Communicating with Other Fragments</a> for more information.
     */
    public interface OnFragmentInteractionListener {
        // TODO: Update argument type and name
        public void onFragmentInteraction(Uri uri);
    }

}

---

希望你们能帮助我。我只是android开发的新手。

找到了答案！！在创建我的导航抽屉时添加了覆盖方法，这就是原因。我尝试创建一个新的NavigationFragmentDrawer类和xml，方法是：右键单击我的java包，然后单击new>fragment>fragment blank此时取消选中Include fragment factory方法和Include接口回调检查本教程的1:30-1:45:

您想在actionbar中同时显示hamburger菜单和back菜单

从代码中删除以下行以仅显示汉堡包菜单

getSupportActionBar().setDisplayShowHomeEnabled(true);

---

你能把整个日志贴出来吗？

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools" android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context="com.serverus.flexibleui.NavigationDrawerFragment">

    <!-- TODO: Update blank fragment layout -->
    <TextView android:layout_width="match_parent" android:layout_height="match_parent"
        android:text="@string/hello_blank_fragment" />

</RelativeLayout>

02-24 13:00:57.319    5096-5096/com.serverus.flexibleui E/AndroidRuntime﹕ FATAL EXCEPTION: main
    java.lang.RuntimeException: Unable to start activity ComponentInfo{com.serverus.flexibleui/com.serverus.flexibleui.MainActivity}: java.lang.NullPointerException
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2351)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2403)
            at android.app.ActivityThread.access$600(ActivityThread.java:165)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1373)
            at android.os.Handler.dispatchMessage(Handler.java:107)
            at android.os.Looper.loop(Looper.java:194)
            at android.app.ActivityThread.main(ActivityThread.java:5391)
            at java.lang.reflect.Method.invokeNative(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:525)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:833)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:600)
            at dalvik.system.NativeStart.main(Native Method)
     Caused by: java.lang.NullPointerException
            at com.serverus.flexibleui.MainActivity.onCreate(MainActivity.java:43)
            at android.app.Activity.performCreate(Activity.java:5122)
            at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1150)
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2315)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2403)
            at android.app.ActivityThread.access$600(ActivityThread.java:165)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1373)
            at android.os.Handler.dispatchMessage(Handler.java:107)
            at android.os.Looper.loop(Looper.java:194)
            at android.app.ActivityThread.main(ActivityThread.java:5391)
            at java.lang.reflect.Method.invokeNative(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:525)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:833)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:600)
            at dalvik.system.NativeStart.main(Native Method)

getSupportActionBar().setDisplayShowHomeEnabled(true);