导航抽屉应用程序在启动时停止响应

Question

我的申请有问题。它包括一个带4个项目的导航抽屉。我有4个片段，每个片段对应于导航抽屉中的一个项目。当我运行应用程序时它崩溃了（“不幸的是，i-CS编辑器已经停止了。”）。我猜我的MainActivity.java有问题。最初应用程序正在运行，但我需要保存片段的当前状态，所以我找到了一个有同样问题的人，并且完全按照他所做的去解决它。在我实施了所谓的解决方案后，应用程序崩溃了。 这是我的MainActivity.java：

package com.wordpress.softwarebycs.i_cseditor;

import android.app.Activity;
import android.content.pm.PackageInstaller;
import android.support.v4.app.FragmentTransaction;
import android.support.v7.app.ActionBarActivity;
import android.support.v7.app.ActionBar;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentManager;
import android.content.Context;
import android.os.Build;
import android.os.Bundle;
import android.view.Gravity;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.ViewGroup;
import android.support.v4.widget.DrawerLayout;
import android.widget.ArrayAdapter;
import android.widget.TextView;


public class MainActivity extends ActionBarActivity
        implements NavigationDrawerFragment.NavigationDrawerCallbacks {

    public static final int CODE=0;
    public static final int SAVE=1;
    public static final int OPEN=2;
    public static final int HELP=3;
    public static final int FRAGMENT_COUNT=4;
    private Fragment[] fragments = new Fragment[FRAGMENT_COUNT];

    /**
     * Fragment managing the behaviors, interactions and presentation of the navigation drawer.
     */
    private NavigationDrawerFragment mNavigationDrawerFragment;

    /**
     * Used to store the last screen title. For use in {@link #restoreActionBar()}.
     */
    private CharSequence mTitle;

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

        mNavigationDrawerFragment = (NavigationDrawerFragment)
                getSupportFragmentManager().findFragmentById(R.id.navigation_drawer);
        mTitle = getTitle();

        // Set up the drawer.
        mNavigationDrawerFragment.setUp(
                R.id.navigation_drawer,
                (DrawerLayout) findViewById(R.id.drawer_layout));

        FragmentManager fm=getSupportFragmentManager();
        fragments[CODE]=fm.findFragmentById(R.id.codeFragment);
        fragments[SAVE]=fm.findFragmentById(R.id.saveFragment);
        fragments[OPEN]=fm.findFragmentById(R.id.openFragment);
        fragments[HELP]=fm.findFragmentById(R.id.helpFragment);

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

    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]);
                fm.executePendingTransactions();
                            }
            else {
                transaction.hide(fragments[i]);
                fm.executePendingTransactions();
            }
        }
        if (addToBackStack) {
            transaction.addToBackStack(null);
            fm.executePendingTransactions();
        }
        transaction.commit();
        fm.executePendingTransactions();
    }


    @Override
    public void onNavigationDrawerItemSelected(int position) {
        // update the main content by replacing fragments

        Fragment objFragment=null;
        switch(position)
        {
            case 0 :
                showFragment(CODE,false);
                break;
            case 1 :
                showFragment(SAVE,false);
                break;
            case 2 :
                showFragment(OPEN,false);
                break;
            case 3 :
                showFragment(HELP,false);
                break;
        }

    }

    public void onSectionAttached(int number) {
        switch (number) {

            case 1:
                mTitle="Code";
                break;
            case 2:
                mTitle = "Save File";
                break;
            case 3:
                mTitle = "Open File";
                break;
            case 4:
                mTitle = "Help";
                break;

        }
    }

    public void restoreActionBar() {
        ActionBar actionBar = getSupportActionBar();
        actionBar.setNavigationMode(ActionBar.NAVIGATION_MODE_STANDARD);
        actionBar.setDisplayShowTitleEnabled(true);
        actionBar.setTitle(mTitle);
    }




    @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);
    }

    /**
     * A placeholder fragment containing a simple view.
     */
    public static class PlaceholderFragment extends Fragment {
        /**
         * The fragment argument representing the section number for this
         * fragment.
         */
        private static final String ARG_SECTION_NUMBER = "section_number";

        /**
         * Returns a new instance of this fragment for the given section
         * number.
         */
        public static PlaceholderFragment newInstance(int sectionNumber) {
            PlaceholderFragment fragment = new PlaceholderFragment();
            Bundle args = new Bundle();
            args.putInt(ARG_SECTION_NUMBER, sectionNumber);
            fragment.setArguments(args);
            return fragment;
        }

        public PlaceholderFragment() {
        }

        @Override
        public View onCreateView(LayoutInflater inflater, ViewGroup container,
                                 Bundle savedInstanceState) {
            View rootView = inflater.inflate(R.layout.fragment_main, container, false);
            return rootView;
        }

        @Override
        public void onAttach(Activity activity) {
            super.onAttach(activity);
            ((MainActivity) activity).onSectionAttached(
                    getArguments().getInt(ARG_SECTION_NUMBER));
        }




    }

}