android :fragmentation使用中遇到的 NullPointerException

背景：fragmentation(单ACTIVITY+多个fragments)+brvah( recyclerView多级自定义菜单功能）

目的：实现菜单栏的点击，fragment 显示相应的内容

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mainActivity.xml

<?xml version="1.0" encoding="utf-8"?>

<android.support.v4.widget.DrawerLayout

    android:id="@+id/drawer_layout"

    xmlns:android="http://schemas.android.com/apk/res/android"

    xmlns:app="http://schemas.android.com/apk/res-auto"

    xmlns:tools="http://schemas.android.com/tools"

    android:layout_width="match_parent"

    android:layout_height="match_parent"

    android:fitsSystemWindows="true"

    tools:openDrawer="start">

    <FrameLayout

        android:id="@+id/fl_container"

        android:layout_width="match_parent"

        android:layout_height="match_parent"

        tools:context=".demo_flow.MainActivity">

    </FrameLayout>

    <RelativeLayout

        android:id="@+id/menu_layout_left"

        android:layout_width="match_parent"

        android:layout_height="match_parent"

        android:layout_gravity="left"

        android:background="@drawable/menu_bg"

        android:layout_marginRight="10dp"

        android:layout_marginTop="57dp" >

        <android.support.v7.widget.RecyclerView

            android:id="@+id/rv"

            android:layout_width="match_parent"

            android:layout_height="match_parent"

            />

    </RelativeLayout>

</android.support.v4.widget.DrawerLayout>

遇到的问题：

1、因为菜单点击显示 fragment

　在菜单的adapter 中要实现对fragment的控制，

我的实现方式：回调函数

（1）菜单的adapter中的部分代码：

private SubClickListener subClickListener;

public void setsubClickListener(SubClickListener topicClickListener) {

    this.subClickListener = topicClickListener;

}


//接口，希望在mainActivity中实现

public interface SubClickListener {

    void OntopicClickListener(View v, int position);

}

protected void convert(final BaseViewHolder holder, final MultiItemEntity item) {

switch (holder.getItemViewType()) {

            case TYPE_LEVEL_0:

                holder.setImageResource(R.id.iv_head, R.mipmap.head_img1);

                final Level0Item lv0 = (Level0Item) item;

                int subTitle = Integer.parseInt(lv0.subTitle.split("_")[0]);

                int itemID = Integer.parseInt(lv0.subTitle.split("_")[1]);

                switch (subTitle)

                {

                    case 1:

                        holder.setImageResource(R.id.iv_head,R.mipmap.head_img0);

                        break;

                    case 2:

                        holder.setImageResource(R.id.iv_head,R.mipmap.head_img1);

                        break;

                    case 3:

                        holder.setImageResource(R.id.iv_head,R.mipmap.head_img2);

                        break;

                    case 4:

                        holder.setImageResource(R.id.iv_head,R.mipmap.head_img2);

                        break;

                    case 5:

                        holder.setImageResource(R.id.iv_head,R.mipmap.head_img2);

                        break;

                }

                //if(subTitle=="1") System.out.println("---------------------level--------------------");

                //System.out.println("---------------------level-int-------------------");

                String name = lv0.title;

                if(name.indexOf(".doc")>0)

                {

                    holder.setTypeface(R.id.title, Typeface.SANS_SERIF);

                    holder.setImageResource(R.id.iv_head,R.mipmap.head_img_1);

                }

                holder.setText(R.id.title, lv0.title)

                        .setText(R.id.sub_title, lv0.subTitle)

                        .setImageResource(R.id.iv, lv0.isExpanded() ? R.mipmap.arrow_b : R.mipmap.arrow_r);

                holder.itemView.setOnClickListener(new View.OnClickListener() {

                    @Override

                    public void onClick(View v) {

                        int pos = holder.getAdapterPosition();

                        if (subClickListener != null) {

                            subClickListener.OntopicClickListener(v,pos);

                        }

                        if (lv0.isExpanded()) {

                            collapse(pos);

                        } else {

                            expand(pos);

                        }

                    }

                });

                break;

              　//此处省略其他分支……

        }

    }

　　（2）mainActivity.java

　　结构如下：

 @Override

    protected void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);

        setContentView(R.layout.activity_main);

        MySupportFragment fragment = findFragment(HomeFragment.class);

        if (fragment == null) {

            loadRootFragment(R.id.fl_container, HomeFragment.newInstance());

        }

        initView();

    }

final ISupportFragment topFragment = getTopFragment();

private void initView() {

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

        ActionBarDrawerToggle toggle = new ActionBarDrawerToggle(

                this, mDrawer, R.string.navigation_drawer_open, R.string.navigation_drawer_close);

//        mDrawer.setDrawerListener(toggle);

        toggle.syncState();

        //added by ssqhan

        mRecyclerView = (RecyclerView)findViewById(R.id.rv);

        list=generateData();

        adapter=new ExpandableItemAdapter(list);

        adapter.setsubClickListener(new ExpandableItemAdapter.SubClickListener() {

            @Override

            public void OntopicClickListener(View v, int position) {  //实现菜单中adapter回调函数

                TextView tv=(TextView)v.findViewById(R.id.title);

                final String wbs_name = (String) tv.getText();

                boolean flag = (tv.getText().toString().indexOf(".doc")>0);

                if(flag)

                {

                    mDrawer.closeDrawer(GravityCompat.START);

                    mDrawer.postDelayed(new Runnable() {

                    @Override

                    public void run() {

                        SartFragment(wbs_name);

                    }

                }, 300);

                }

            }

        });

        //adapter.get

        manager = new LinearLayoutManager(this);

        mRecyclerView.setAdapter(adapter);

        //important! setLayoutManager should be called after setAdapter

        mRecyclerView.setLayoutManager(manager);

        adapter.expandAll();

}

public void SartFragment(String tableName)

    {

        HomeFragment fragment=null;

        DiscoverFragment discoverFragment0=null;

        Bundle newBundle = new Bundle();

        System.out.println("---------------discovery---------------");

        switch (tableName) {

            case "避雷器实验报告.doc":

                fragment = findFragment(HomeFragment.class);

                newBundle.putString("from", "From:" + topFragment.getClass().getSimpleName());

                fragment.putNewBundle(newBundle);

                start(fragment, SupportFragment.SINGLETASK);

                break;

            case "电缆头施工记录.doc":

                discoverFragment0 = findFragment(DiscoverFragment.class);

                if (discoverFragment0 == null) {

                    popTo(HomeFragment.class, false, new Runnable() {

                        @Override

                        public void run() {

                            start(DiscoverFragment.newInstance());

                            Bundle myBundle = new Bundle();

                            DiscoverFragment discoverFragment=null;

                            if(topFragment==null) {
　　　　　　　　　　　　　　　　　　　//这个地方，发现 topFragment 是空一直都是空

                                System.out.println("---------------------------------------");

                                System.out.println("----------topFragment is null----------");

                                System.out.println("---------------------------------------");
　　　　　　　　　　　　　　　　　　　

                                //loadRootFragment(R.id.fl_container, HomeFragment.newInstance());

                            }

                            myBundle.putString("from", "From:" + topFragment.getClass().getSimpleName());

                            discoverFragment.putNewBundle(myBundle);

                            start(discoverFragment, SupportFragment.SINGLETASK);

                        }

                    });

                }

                else

                {

                    newBundle.putString("from", "From:" + topFragment.getClass().getSimpleName());

                    discoverFragment0.putNewBundle(newBundle);

                    start(discoverFragment0, SupportFragment.SINGLETASK);

                }

                break;

        }

    }

问题：如何解决，这个一直为空？？？

巴特西

android :fragmentation使用中遇到的 NullPointerException

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