Java 在包含RecyclerView的片段之间切换时出现NullPointerException

我真的很难弄明白这一点。当使用

RecyclerView

在

片段之间切换时，我得到一个
NullPointerException
，但只能按特定顺序切换。下面是代码和异常。首先是解释：

我有一个带有此选项卡式布局的片段，如下所示：

其中3个选项卡使用包含RecyclerView的相同片段：Schedule、History和Test。如果我先选择它们，它们中的任何一个都可以工作。现在的问题是，当我转到前面提到的第一个选项卡右侧的另一个选项卡时！但是，如果我转到我选择的第一个选项的左侧，则可以加载

如果我选择测试，然后去历史，然后安排一切都会很好

如果我选择Test，那么这两个计划将起作用，但是转到History将导致
例外

如果我选择Schedule，则会发生异常

如果我选择History，那么调度这两个将起作用，但是接下来要测试异常将发生

如果我选择History，那么将发生异常测试

我扩展了RecycleView，并在测量中中断了
onMeasure
，看看我是否能找出发生了什么，我注意到
RecycleView
的
mAdapter
是
null
。我检查了
RecyclerView
的
setAdapter（）
内部，它总是被传递一个有效的适配器。因此，
mAdapter
似乎在某个时候被清除了。我只是不明白为什么只有当我从左到右而不是从右到左打开选项卡时才会发生这种情况

如果有任何帮助，我将不胜感激，因为我已智穷于此

以下是NullPointerException：

（必须放在这里以避免字符限制）

编辑：捕获
NullPointerException
后，也会弹出一个
IllegalStateException
。看起来来自
布局管理器

以下是选项卡式视图的片段：

public class FKitViewer extends Fragment implements OnTabChangeListener {

    public static final String TAB_INFO = "Info";
    public static final String TAB_SCHEDULE = "Schedule";
    public static final String TAB_HISTORY = "History";
    public static final String TAB_TEST = "Test";
    public static final String TAB_REQS = "Reqs";

    private View mRoot;
    private TabHost mTabHost;
    private int mCurrentTab;

    @Override
    public void onAttach(Activity activity){
        super.onAttach(activity);
    }

    @Override
    public View onCreateView(LayoutInflater li, ViewGroup container,
                                Bundle savedInstanceState){
        mRoot = li.inflate(R.layout.kit_view, container);
        mTabHost = (TabHost) mRoot.findViewById(android.R.id.tabhost);
        setupTabs();
        return mRoot;
    }

    @Override
    public void onActivityCreated(Bundle savedInstanceState){
        super.onActivityCreated(savedInstanceState);
        setRetainInstance(true);
        mTabHost.setOnTabChangedListener(this);
        mTabHost.setCurrentTab(mCurrentTab);
        updateTab(TAB_INFO, R.id.tab1);
    }

    private void setupTabs(){
        mTabHost.setup();
        mTabHost.addTab(newTab(TAB_INFO, "Info", R.id.tab1));
        mTabHost.addTab(newTab(TAB_SCHEDULE, "Schedule", R.id.tab2));
        mTabHost.addTab(newTab(TAB_HISTORY, "History", R.id.tab3));
        mTabHost.addTab(newTab(TAB_REQS, "Reqs", R.id.tab4));
        mTabHost.addTab(newTab(TAB_TEST, "Test", R.id.tab5));
    }

    private TabSpec newTab(String tag, String label, int tabContentId){
        TabSpec tabSpec = mTabHost.newTabSpec(tag);
        tabSpec.setIndicator(label);
        tabSpec.setContent(tabContentId);
        return tabSpec;
    }

    private void updateTab(String tabId, int placeholder){
        FragmentManager fm = getFragmentManager();
        if(fm.findFragmentByTag(tabId) == null){
            if(tabId.equals(TAB_INFO))
                fm.beginTransaction()
                    .replace(placeholder, new FListiesView(), tabId)
                    .commit();
            if(tabId.equals(TAB_SCHEDULE))
                fm.beginTransaction()
                    .replace(placeholder, new FKitSchedule(false), tabId)
                    .commit();
            if(tabId.equals(TAB_HISTORY))
                fm.beginTransaction()
                    .replace(placeholder, new FKitSchedule(true), tabId)
                    .commit();
            if(tabId.equals(TAB_REQS))
                fm.beginTransaction()
                    .replace(placeholder, new KitRequirements(), tabId)
                    .commit();
            if(tabId.equals(TAB_TEST))
                fm.beginTransaction()
                    .replace(placeholder, new FKitSchedule(false), tabId)
                    .commit();
        }
    }

    @Override
    public void onTabChanged(String tabId){
        Log.d("MNB", "Changing to tab: " + tabId);
        if(TAB_INFO.equals(tabId)){
            updateTab(tabId, R.id.tab1);
            mCurrentTab = 0;
            return;
        }
        if(TAB_SCHEDULE.equals(tabId)){
            getActivity().getIntent().getExtras().putBoolean("com.crummy.history", false);
            updateTab(tabId, R.id.tab2);
            mCurrentTab = 1;
            return;
        }
        if(TAB_HISTORY.equals(tabId)){
            getActivity().getIntent().getExtras().putBoolean("com.crummy.history", true);
            updateTab(tabId, R.id.tab3);
            mCurrentTab = 2;
            return;
        }
        if(TAB_REQS.equals(tabId)){
            updateTab(tabId, R.id.tab4);
            mCurrentTab = 3;
            return;
        }
        if(TAB_TEST.equals(tabId)){
            getActivity().getIntent().getExtras().putBoolean("com.crummy.history", true);
            updateTab(tabId, R.id.tab5);
            mCurrentTab = 4;
            return;
        }
    }
}

以下是片段：

public class RVFKitSchedule extends Fragment 

实现LoaderManager.LoaderCallbacks{

private String mGetURL = "/index.php/droid/kitreport/";
private String mHistoryURL = "/index.php/droid/kithistory/";
private String mUpdateStatusURL = "/index.php/order_status/update/";
private Boolean mIsHistory = false;

private LinearLayout mPbl;

private int mDialogStatusLevel = 0;
private int mDialogLineId = -1;

private List<ScheduleRowModel> mItems = null;
private FKVRecyclerView mRecyclerView;
private KitScheduleRVAdapter mRVAdapter;
private int mItemCount;
private RecyclerView.LayoutManager mLayoutManager;

private FragmentActivity mParentActivity;

public RVFKitSchedule(){

}

public RVFKitSchedule(boolean isHistory){
    mIsHistory = isHistory;
    if(mIsHistory)
        mGetURL = mHistoryURL;
}

@Override
public View onCreateView(LayoutInflater li, ViewGroup vg, Bundle b){
    super.onCreateView(li, vg, b);
    return li.inflate(R.layout.rv_main, vg, false);
}


@Override
public void onActivityCreated(Bundle icicle){
    super.onActivityCreated(icicle);

    final InputMethodManager imm = (InputMethodManager) mParentActivity.getSystemService(Context.INPUT_METHOD_SERVICE);
    imm.hideSoftInputFromWindow(getView().getWindowToken(), 0);
}

@Override
public void onViewCreated(View view, Bundle icicle){
    super.onViewCreated(view, icicle);
    mParentActivity = getActivity();
    mRecyclerView = (FKVRecyclerView)mParentActivity.findViewById(R.id.recyclerView);
    mLayoutManager = new LinearLayoutManager(mParentActivity);

    //mLayoutManager.setOrientation(LinearLayoutManager.VERTICAL);
    //mLayoutManager.
    mLayoutManager.scrollToPosition(0);
    mRecyclerView.setLayoutManager(mLayoutManager);

    RecyclerView.ItemDecoration itemDecoration = 
            new DividerItemDecoration(mParentActivity, DividerItemDecoration.VERTICAL_LIST);
    mRecyclerView.addItemDecoration(itemDecoration);
    mItems = new ArrayList<ScheduleRowModel>();
    mRVAdapter = new KitScheduleRVAdapter(mItems, mIsHistory);
    //mRecyclerView.setAdapter(null);
    if(mRecyclerView.getAdapter() != null)
        mRecyclerView.swapAdapter(mRVAdapter, true);
    else
        mRecyclerView.setAdapter(mRVAdapter);

    mRecyclerView.addOnItemTouchListener(
            new RecyclerItemClickListener(mParentActivity, new RecyclerItemClickListener.OnItemClickListener(){
                @Override
                public void onItemClick(View v, int position){
                    String status = ((TextView)v.findViewById(R.id.sr_status)).getText().toString();
                    if(status.equals("Open"))
                        mDialogStatusLevel = 0;
                    else if(status.equals("In Production"))
                        mDialogStatusLevel = 1;
                    else if(status.equals("Waiting"))
                        mDialogStatusLevel = 2;
                    else if(status.equals("Ready"))
                        mDialogStatusLevel = 3;
                    else if(status.equals("Shipped"))
                        mDialogStatusLevel = 4;
                    int lineId = Integer.parseInt(((TextView)v.findViewById(R.id.sr_order_line_id)).getText().toString());
                    mDialogLineId = lineId;
                    OrderStatusDialog df = new OrderStatusDialog(mParentActivity, mDialogStatusLevel){
                        @Override
                        protected void onDialogClick(DialogInterface di, final int which){
                            Runnable update = new Runnable(){
                                @Override
                                public void run(){
                                    updateStatus(mDialogLineId, which);
                                }
                            };
                            Thread t = new Thread(null, update, "MagentoBackground");
                            t.start();
                            try{
                                t.join();
                            }catch(InterruptedException e){
                                e.printStackTrace();
                            }
                            restartLoading();
                            dismiss();
                        }
                    };
                    df.show(getFragmentManager(), "dialog");
                }
            }){
                @Override
                public void onItemLongClick(View v, int pos){
                    String s = ((TextView)v.findViewById(R.id.sr_pn)).getText().toString();
                    String n = ((TextView)v.findViewById(R.id.sr_pn)).getText().toString();

                    CheckItemTypeTask task = new CheckItemTypeTask(s, null);
                    task.execute(mParentActivity);
                    int type = -1;
                    try{
                        type = task.get();
                    }catch(Exception e){
                        e.printStackTrace();
                    }
                    if(type == ItemType.PART){
                        openPartViewer(s);
                    }else if(type == ItemType.KIT){
                        openKitViewer(s,n);
                    }else if(type == ItemType.ERROR){
                        Toast.makeText(mParentActivity, "Error getting item type!", Toast.LENGTH_LONG);
                    }else{
                        Toast.makeText(mParentActivity, "Invalid item type!", Toast.LENGTH_LONG).show();
                    }
                }
            }
    );

    if(mParentActivity.getIntent().getExtras() != null){
        Bundle b = mParentActivity.getIntent().getExtras();
        if(!b.isEmpty()){
            mGetURL += b.getString("com.crummy.kitNum");
        }
    }

    mPbl = (LinearLayout)mParentActivity.findViewById(R.id.main_pbl);
    mPbl.setVisibility(View.VISIBLE);


    LoaderManager lm = getLoaderManager();
    if(lm.getLoader(0) != null){
        lm.initLoader(0, null, this);
    }
    startLoading();
}

protected void startLoading(){
    getLoaderManager().initLoader(0, null, this);
}

protected void restartLoading(){
    getLoaderManager().restartLoader(0, null, this);
}

@Override
public Loader<Void> onCreateLoader(int arg0, Bundle arg1){
    Log.d("MNB", "FKitSchedule: onCreateLoader");
    AsyncTaskLoader<Void> loader = new AsyncTaskLoader<Void>(mParentActivity){
        @Override
        public Void loadInBackground(){
            try{
                getLines();
            }catch(Exception e){
                e.printStackTrace();
            }
            return null;
        }
    };
    loader.forceLoad();
    return loader;
}

@Override
public void onLoadFinished(Loader<Void> arg0, Void arg1){
    Log.d("MNB", "FKitSchedule: onLoadFinished");
    mPbl.setVisibility(View.GONE);
}

@Override
public void onLoaderReset(Loader<Void> arg0){

}

protected boolean openKitViewer(String kitNum, String kitName){
    boolean result = false;
    Intent i = new Intent(mParentActivity, GenFragmentActivity.class);
    i.putExtra("com.crummy.frag_layout_id", R.layout.kit_view_frag);
    i.putExtra("com.crummy.kitNum", kitNum);
    i.putExtra("com.crummy.kitName", kitName);
    startActivity(i);
    return result;
}

protected boolean openPartViewer(String itemNum){
    boolean result = false;
    Intent i = new Intent(mParentActivity, PartInfoFragmentActivity.class);
    i.putExtra("com.crummy.partnum", itemNum);
    startActivity(i);
    return result;
}

protected void getLines(){
    Log.d("MNB", "FKitSchedule: getLines() ");
    try{
        HttpEntity response = HttpHelper.tryHttp(mParentActivity, mGetURL, null);
        if(response == null)
            return;
        String res = EntityUtils.toString(response);
        if(res.equals("[]")){
            mParentActivity.runOnUiThread(noKitsError);
            return;
        }
        JSONArray jsona = new JSONArray(res);
        mItems = new ArrayList<ScheduleRowModel>();
        Log.d("MNB", "jsona.length() = " + jsona.length());
        for(int i=0; i < jsona.length(); i++){
            Log.d("MNB", "Reading json line " + i);
            JSONObject j = (JSONObject) jsona.get(i);
            ScheduleRowModel srm = new ScheduleRowModel();
            srm.custPo = j.getString("custPo");
            srm.dueDate = j.getString("dueDate");
            srm.partNum = j.getString("KitNumber");
            srm.qty = j.getInt("quantity");
            srm.status = j.getString("status");
            srm.lineId = j.getInt("id");
            srm.company = j.getString("name");
            srm.rev = j.getString("rev");
            if(!mIsHistory){
                if(!j.getString("note").equals("null"))
                    srm.note = j.getString("note");
            }
            mItems.add(srm);
        }
    }catch(Exception e){
        e.printStackTrace();
    }
    mParentActivity.runOnUiThread(returnRes);
}

private void addItemToList(ScheduleRowModel model){
    mItemCount++;       
    mRVAdapter.addData(model);
}

private HttpEntity updateStatus(int lineId, int statusId){
    HttpEntity resEntityPost = null;
    try{
        HttpClient client = new DefaultHttpClient();
        String host = HttpHelper.getHost(mParentActivity);
        HttpPost post = new HttpPost(host + mUpdateStatusURL);
        List<NameValuePair> nameValuePairs = new ArrayList<NameValuePair>(2);
        nameValuePairs.add(new BasicNameValuePair("line_id", Integer.toString(lineId)));
        nameValuePairs.add(new BasicNameValuePair("status", Integer.toString(statusId)));
        post.setEntity(new UrlEncodedFormEntity(nameValuePairs));
        HttpResponse res = client.execute(post);
        resEntityPost = res.getEntity();
    }catch(Exception e){
        e.printStackTrace();
    }
    return resEntityPost;
}
protected Runnable returnRes = new Runnable(){
    @Override
    public void run(){
        Log.d("MNB", "FKitSchedule returnRes ");
        mItemCount = 0;
        mRVAdapter.clear();
        if(mItems != null && mItems.size() > 0){
            for(int i = 0; i < mItems.size(); i++){
                addItemToList(mItems.get(i));
            }
        }
    }
};

private Runnable noKitsError = new Runnable()
{
    public void run(){
        Toast t = Toast.makeText(mParentActivity, "No orders for this kit.", Toast.LENGTH_SHORT);
        t.show();
    }
};

私有字符串mGetURL=“/index.php/droid/kitreport/”；
私有字符串mHistoryURL=“/index.php/droid/kithistory/”；
私有字符串mUpdateStatusURL=“/index.php/order_status/update/”；
私有布尔错误历史=false；
私人线路布局mPbl；
private int mDialogStatusLevel=0；
私有int-mDialogLineId=-1；
私有列表m=null；
私人FKVRecyclerView mRecyclerView；
专用KitSchedulerAdapter MRVAAdapter；
私有内部mItemCount；
private RecyclerView.LayoutManager MLLayoutManager；
私人碎片活动；
公共RVFKitSchedule（）{
}
公共RVFKitSchedule（布尔值）{
错误历史=故事；
if（错误历史）
mGetURL=mHistoryURL；
}
@凌驾
创建视图上的公共视图（Layoutiner li、视图组vg、捆绑包b）{
super.onCreateView（li、vg、b）；
回油管充气（右布局rv_总管、vg、假）；
}
@凌驾
已创建活动上的公共空白（捆绑冰柱）{
超级活性创造（冰柱）；
最终InputMethodManager imm=（InputMethodManager）mParentActivity.getSystemService（Context.INPUT\u方法\u服务）；
imm.hideSoftInputFromWindow（getView（）.getWindowToken（），0）；
}
@凌驾
已创建公用void onview（视图、捆绑冰柱）{
super.onViewCreated（视图、冰柱）；
mParentActivity=getActivity（）；
mRecyclerView=（FKVRecyclerView）mParentActivity.findViewById（R.id.recyclerView）；
mLayoutManager=新的LinearLayoutManager（mParentActivity）；
//mLayoutManager.setOrientation（LinearLayoutManager.VERTICAL）；
//我是经理。
mLayoutManager.scrollToPosition（0）；
mRecyclerView.setLayoutManager（mllayoutmanager）；
RecyclerView.ItemDecoration ItemDecoration=
新的DividerItemDecoration（mParentActivity，DividerItemDecoration.VERTICAL_LIST）；
mRecyclerView.附加装饰（项目装饰）；
mItems=新的ArrayList（）；
mRVAdapter=新的KitSchedulerAdapter（mItems，错误历史）；
//mRecyclerView.setAdapter（null）；
if（mRecyclerView.getAdapter（）！=null）
mRecyclerView.swapAdapter（mRVAdapter，true）；
其他的
mRecyclerView.setAdapter（mRVAdapter）；
mRecyclerView.addonimtouchlistener(
新的RecyclerItemClickListener（mParentActivity，新的RecyclerItemClickListener.OnItemClickListener（）{
@凌驾
公共空间单击（视图v，内部位置）{
字符串状态=（（TextView）v.findviewbyd（R.id.sr_status））.getText（）.toString（）；
if（状态等于（“打开”））
mDialogStatusLevel=0；
否则，如果（状态等于（“生产中”））
mDialogStatusLevel=1；
else if（status.equals（“Waiting”））
mDialogStatusLevel=2；
else if（status.equals（“Ready”））
mDialogStatusLevel=3；
else if（状态等于（“已装运”））
mDialogStatusLevel=4；
int lineId=Integer.parseInt（（（TextView）v.findViewById（R.id.sr_order_line_id））.getText（）.toString（））；
mDialogLineId=lineId；
OrderStatusDialog df=新建OrderStatusDialog（mParentActivity，mDialogStatusLevel）{
@凌驾
受保护的void onDialogClick（对话框接口di，最终整数）{
Runnable update=new Runnable（）{
@凌驾
公开募捐{
updateStatus（mDialogLineId，其）；
}
};
线程t=新线程（null，更新，“MagentoBackground”）；
t、 start（）；
import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Calendar;
import java.util.Date;
import java.util.List;
import java.util.Locale;

import android.support.v7.widget.RecyclerView;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;

public class KitScheduleRVAdapter extends RecyclerView.Adapter<KitScheduleRVAdapter.ScheduleRowViewHolder>{

    private List<ScheduleRowModel> items;
    private boolean mIsHistory = false;

    KitScheduleRVAdapter(List<ScheduleRowModel> modelData, boolean isHistory){
        Log.d("MNB", "Constructing KitScheduleRVAdapter");
        if(modelData == null){
            throw new IllegalArgumentException(
                    "modelData must not be null");
        }
        this.items = modelData;
        mIsHistory = isHistory;
    }

    @Override
    public ScheduleRowViewHolder onCreateViewHolder(ViewGroup vg, int viewType){
        Log.d("MNB", "KitScheduleRVAdapter.onCreateViewHolder()");
        View itemView = LayoutInflater
                        .from(vg.getContext())
                        .inflate(R.layout.schedule_row, vg, false);
        return new ScheduleRowViewHolder(itemView);
    }

    @Override
    public void onBindViewHolder(ScheduleRowViewHolder vh, int pos){
        Log.d("MNB", "Binding Viewholder at pos "+pos);
        ScheduleRowModel model = items.get(pos);
        vh.date.setText(model.dueDate);
        vh.po.setText(model.custPo);
        vh.partnum.setText(model.partNum);
        vh.qty.setText(""+model.qty);
        vh.status.setText(model.status);
        vh.id.setText(""+model.lineId);
        vh.company.setText(model.company);
        vh.rev.setText(model.rev);
        vh.note.setText(model.note);

        Calendar cutoff = Calendar.getInstance();
        cutoff.add(Calendar.DAY_OF_MONTH, 14);
        Date co = cutoff.getTime();

        SimpleDateFormat s = new SimpleDateFormat("yyyy-MM-dd", Locale.US);
        Date d = new Date();
        try {
            d = s.parse(model.dueDate);
        } catch (ParseException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        View statusBar = vh.statusBar;
        if(!mIsHistory){
            if(model.status.equals("Ready")){
                statusBar.setBackgroundResource(R.color.sh_ready);
            }else if(model.status.equals("Waiting")){
                statusBar.setBackgroundResource(R.color.sh_waiting);
            }else if(model.status.equals("In Production")){
                statusBar.setBackgroundResource(R.color.sh_inprod);
            }
            else if(d.before(co)){
                statusBar.setBackgroundResource(R.color.sh_soon);
            }else{
                statusBar.setBackgroundResource(R.color.sh_open);
            }
        }
        else
        {
            statusBar.setBackgroundResource(R.color.sh_ready);
        }
    }

    @Override
    public int getItemCount(){
        return items.size();
    }

    public void addData(ScheduleRowModel data){
        items.add(data);
        this.notifyItemInserted(items.size() - 1);
    }

    public void clear(){
        Log.d("MNB", "KitScheduleRVAdapter.clear()");
        int itemsCleared = items.size();
        items.clear();
        notifyItemRangeRemoved(0, itemsCleared);
    }

    public final static class ScheduleRowViewHolder extends RecyclerView.ViewHolder{
        TextView date;
        TextView po;
        TextView qty;
        TextView partnum;
        TextView status;
        TextView id;
        TextView company;
        TextView rev;
        TextView note;
        View statusBar;

        public ScheduleRowViewHolder(View itemView){
            super(itemView);
            date = (TextView) itemView.findViewById(R.id.sr_date);
            po = (TextView) itemView.findViewById(R.id.sr_po);
            qty = (TextView) itemView.findViewById(R.id.sr_qty);
            partnum = (TextView) itemView.findViewById(R.id.sr_pn);
            status = (TextView) itemView.findViewById(R.id.sr_status);
            id = (TextView) itemView.findViewById(R.id.sr_order_line_id);
            company = (TextView) itemView.findViewById(R.id.sr_company);
            rev = (TextView) itemView.findViewById(R.id.sr_rev);
            note = (TextView) itemView.findViewById(R.id.sr_note);
            statusBar = itemView.findViewById(R.id.sr_status_bar);
        }
    }
}