导航抽屉Recycler View空指针异常

时间：2016-02-08 18:56:51

标签： android android-recyclerview recycler-adapter

我正在使用recycleView作为材料设计教程，我已完成所有相关但我的logCat说：

E/AndroidRuntime: FATAL EXCEPTION: main Process: com.portal.college.myapplication, PID: 6541 java.lang.NullPointerException 
 at android.support.v7.widget.RecyclerView$Adapter.createViewHolder(RecyclerView.java:5229) 
 at android.support.v7.widget.RecyclerView$Recycler.getViewForPosition(RecyclerView.java:4453)
 at android.support.v7.widget.RecyclerView$Recycler.getViewForPosition(RecyclerView.java:4363)
 at android.support.v7.widget.LinearLayoutManager$LayoutState.next(LinearLayoutManager.java:1961)
 at android.support.v7.widget.LinearLayoutManager.layoutChunk(LinearLayoutManager.java:1370)
 at android.support.v7.widget.LinearLayoutManager.fill(LinearLayoutManager.java:1333)
 at android.support.v7.widget.LinearLayoutManager.onLayoutChildren(LinearLayoutManager.java:562)
 at android.support.v7.widget.RecyclerView.dispatchLayout(RecyclerView.java:2900)
 at android.support.v7.widget.RecyclerView.onLayout(RecyclerView.java:3071)
 at android.view.View.layout(View.java:14817)
 at android.view.ViewGroup.layout(ViewGroup.java:4631)
 at android.widget.RelativeLayout.onLayout(RelativeLayout.java:1055)
 at android.view.View.layout(View.java:14817)
 at android.view.ViewGroup.layout(ViewGroup.java:4631)
 at android.support.v4.widget.DrawerLayout.onLayout(DrawerLayout.java:1067)
 at android.view.View.layout(View.java:14817)
 at android.view.ViewGroup.layout(ViewGroup.java:4631)
 at android.widget.FrameLayout.layoutChildren(FrameLayout.java:453)
 at android.widget.FrameLayout.onLayout(FrameLayout.java:388)
 at android.view.View.layout(View.java:14817)
 at android.view.ViewGroup.layout(ViewGroup.java:4631)
 at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1671)
 at android.widget.LinearLayout.layoutVertical(LinearLayout.java:1525)
 at android.widget.LinearLayout.onLayout(LinearLayout.java:1434)
 at android.view.View.layout(View.java:14817)
 at android.view.ViewGroup.layout(ViewGroup.java:4631)
 at android.widget.FrameLayout.layoutChildren(FrameLayout.java:453)
 at android.widget.FrameLayout.onLayout(FrameLayout.java:388)
 at android.view.View.layout(View.java:14817)
 at android.view.ViewGroup.layout(ViewGroup.java:4631)
 at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1671)
 at android.widget.LinearLayout.layoutVertical(LinearLayout.java:1525)
 at android.widget.LinearLayout.onLayout(LinearLayout.java:1434)
 at android.view.View.layout(View.java:14817)
 at android.view.ViewGroup.layout(ViewGroup.java:4631)
 at android.widget.FrameLayout.layoutChildren(FrameLayout.java:453)
 at android.widget.FrameLayout.onLayout(FrameLayout.java:388)
 at android.view.View.layout(View.java:14817)
 at android.view.ViewGroup.layout(ViewGroup.java:4631)
 at android.view.ViewRootImpl.performLayout(ViewRootImpl.java:1983)
 at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1740)
 at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:996)
 at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:5600)
 at android.view.Choreographer$CallbackRecord.run(Choreographer.java:761)
 at android.view.Choreographer.doCallbacks(Choreographer.java:574)
 at android.view.Choreographer.doFrame(Choreographer.java:544)
 at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:747)
 at android.os.Handler.handleCallback(Handler.java:733)
 at android.os.Handler.dispatchMessage(Handler.java:95)
 at android.os.Looper.loop(Looper.java:136)
 at android.app.ActivityThread.main(ActivityThread.java:5001)
 at java.lang.reflect.Method.invokeNative(Native Method)
 at java.lang.reflect.Method.invoke(Method.java:515)
 at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:785)
 at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:601)
 at dalvik.system.NativeStart.main(Native Method)

main_layout.xml 

 <?xml version="1.0" encoding="utf-8"?>
<android.support.v4.widget.DrawerLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:id="@+id/drawer_layout"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:elevation="7dp">
    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:orientation="vertical">
        <include
            android:id="@+id/app_bar"
            layout="@layout/app_bar_main"  />
   </LinearLayout>
    <fragment
        android:id="@+id/fragment_navigation_drawer"
        android:layout_width="280dp"
        android:layout_height="match_parent"
        android:layout_gravity="start"
        app:layout="@layout/fragment_navigation_drawer"
        android:name="com.portal.college.myapplication.NavigationDrawerFragment"
        tools:layout="@layout/fragment_navigation_drawer"
        />   
</android.support.v4.widget.DrawerLayout>

片段布局xml文件是： fragment_navigation_drawer.xml 

<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"
android:background="#8c8c8c"
tools:context="com.portal.college.myapplication.NavigationDrawerFragment">

<include
    android:id="@+id/nav_head"
    layout="@layout/nav_header_main"  />
<android.support.v7.widget.RecyclerView
    android:id="@+id/drawerList"
    android:layout_width="match_parent"

    android:layout_height="wrap_content"
    >
</android.support.v7.widget.RecyclerView>

</RelativeLayout>

现在的MainActivity.java 

 package com.portal.college.myapplication;

import android.content.Intent;
import android.os.Bundle;
import android.support.design.widget.FloatingActionButton;
import android.support.design.widget.Snackbar;
import android.support.v7.widget.RecyclerView;
import android.view.View;
import android.support.design.widget.NavigationView;
import android.support.v4.view.GravityCompat;
import android.support.v4.widget.DrawerLayout;
import android.support.v7.app.ActionBarDrawerToggle;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;
import android.view.Menu;
import android.view.MenuItem;

public class MainActivity extends AppCompatActivity
        implements NavigationView.OnNavigationItemSelectedListener {
private RecyclerView recyclerView;
    private Toolbar toolbar;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        toolbar = (Toolbar) findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);
getSupportActionBar().setDisplayShowHomeEnabled(true);
        NavigationDrawerFragment drawerFragment = (NavigationDrawerFragment)
                getSupportFragmentManager().findFragmentById(R.id.fragment_navigation_drawer);

        drawerFragment.setUp((DrawerLayout) findViewById(R.id.drawer_layout),toolbar);

        FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);
        fab.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Snackbar.make(view, "Replace with your own action", Snackbar.LENGTH_LONG)
                        .setAction("Action", null).show();
            }
        });

    }

    @Override
    public void onBackPressed() {
        DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
        if (drawer.isDrawerOpen(GravityCompat.START)) {
            drawer.closeDrawer(GravityCompat.START);
        } else {
            super.onBackPressed();
        }
    }

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

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        int id = item.getItemId();
        if(id == R.id.action_settings) {
            return true;
        }
        if(id == R.id.search) {
             startActivity(new Intent(this, SearchActivity.class));
        }

        return super.onOptionsItemSelected(item);

    }

    @SuppressWarnings("StatementWithEmptyBody")
    @Override
    public boolean onNavigationItemSelected(MenuItem item) {
        // Handle navigation view item clicks here.
        int id = item.getItemId();

        DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
        drawer.closeDrawer(GravityCompat.START);
        return true;
    }
}

NavigationDrawerFragment.java 

package com.portal.college.myapplication;
import android.app.Activity;
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.support.v4.widget.DrawerLayout;
import android.support.v7.app.ActionBarDrawerToggle;
import android.support.v7.widget.LinearLayoutManager;
import android.support.v7.widget.RecyclerView;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.support.v7.widget.Toolbar;

import java.util.ArrayList;
import java.util.List;

    public class NavigationDrawerFragment extends Fragment {
        private ActionBarDrawerToggle mDrawerToggle;
        private DrawerLayout mDrawerLayout;
        private RecyclerView recyclerView;
    private VivzAdapter adapter;
        public NavigationDrawerFragment() {
            // Required empty public constructor
        }


        @Override
        public View onCreateView(LayoutInflater inflater, ViewGroup container,
                                 Bundle savedInstanceState) {
            // Inflate the layout for this fragment
            View layout = inflater.inflate(R.layout.fragment_navigation_drawer,container,false);
            recyclerView = (RecyclerView) layout.findViewById(R.id.drawerList);
            adapter = new VivzAdapter(getActivity(),getData());

            recyclerView.setLayoutManager(new LinearLayoutManager(getActivity()));
            recyclerView.setAdapter(adapter);
            return layout;
        }
        public static List<Information> getData(){
            List<Information> data = new ArrayList<>();
            int icons[] = {
                    R.drawable.ic_menu_camera,
                    R.drawable.ic_menu_gallery,
                    R.drawable.ic_menu_manage,
                    R.drawable.ic_menu_send};
            String[] title = {"Camera","Gallery","Settings","Send"};
            for(int i=0;i<title.length && i<icons.length;i++){
                Information current = new Information();
                current.iconId = icons[i];
                current.title = title[i];
                data.add(current);
            }
            return data;

        }


        public void setUp(DrawerLayout drawerLayout,Toolbar toolbar) {
            mDrawerLayout = drawerLayout;
            mDrawerToggle = new ActionBarDrawerToggle(getActivity(), drawerLayout, toolbar, R.string.navigation_drawer_open, R.string.navigation_drawer_close){
                public void onDrawerOpened(View drawerView){
                    super.onDrawerOpened(drawerView);

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

                }

            };
            mDrawerLayout.setDrawerListener(mDrawerToggle);
            mDrawerLayout.post(new Runnable() {

                @Override
                public void run() {
                    mDrawerToggle.syncState();
                }
            });
          /*  containerView = getActivity().findViewById(fragment_id);
            mDrawerLayout=drawerLayout;
            mDrawerToggle = new ActionBarDrawerToggle(getActivity(), drawerLayout, toolbar, R.string.open_drawer,R.string.close_drawer){
                @SuppressLint("NewApi")
                public void onDrawerOpened(View drawerView){
                    super.onDrawerOpened(drawerView);
                     if(!mUserLearnedDrawer){
                         mUserLearnedDrawer = false;
                         saveToPreferences(getActivity(),KEY_USER_LEARNED_DRAWER, mUserLearnedDrawer+"");
                     }
                     getActivity().invalidateOptionsMenu();
                     */
                }

    }

适配器类是VivzAdapter.cjava 

    package com.portal.college.myapplication;

import android.content.Context;
import android.support.v7.widget.RecyclerView;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ImageView;
import android.widget.TextView;

import java.util.Collections;
import java.util.List;

/**
 * Created by admin on 08-Feb-16.
 */
public class VivzAdapter extends RecyclerView.Adapter<VivzAdapter.MyViewHolder>{
    private final LayoutInflater inflater;
    List<Information> data = Collections.emptyList();

    public VivzAdapter(Context context,List<Information> data){
    inflater=LayoutInflater.from(context);
        this.data=data;
}
    @Override
    public MyViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        View view = inflater.inflate(R.layout.custom_row,parent,false);
        MyViewHolder holder = new MyViewHolder(view);
        return null;
    }


    @Override
    public void onBindViewHolder(MyViewHolder holder, int position) {
Information current = data.get(position);
        holder.title.setText(current.title);
        holder.id.setImageResource(current.iconId);
    }

    @Override
    public int getItemCount() {

            return data.size();

    }
class MyViewHolder extends RecyclerView.ViewHolder{
    TextView title;
    ImageView id;

    public MyViewHolder(View itemView) {
        super(itemView);
        title = (TextView) itemView.findViewById(R.id.listText);
        id = (ImageView) itemView.findViewById(R.id.listIcon);
    }
}
}

列表Item类是Information.java 

  package com.portal.college.myapplication;

/**
 * Created by admin on 08-Feb-16.
 */
public class Information {
    int iconId;
    String title;
}

列表行布局是custom_row.xml 

    <?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="horizontal" android:layout_width="match_parent"
    android:layout_height="match_parent">
<ImageView
    android:id="@+id/listIcon"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:src="@drawable/ic_menu_camera"/>
    <TextView
        android:id="@+id/listText"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Camera"
        />
         </LinearLayout>

我已经完成了有关同一问题的stackoverflow上的大多数解决方案，但我在这里失败了。

有一件事我注意到在VivzAdapter.java中，获取数据getItemCount()的函数名称Count会返回data.size()，当我将其更改为0时它在没有recyclerView的情况下工作，但是当与data.size()一起返回时，它会提供NullPointerException。

希望我已经详细解释了所有内容。

任何建议都会非常感激

2 个答案:

答案 0 :(得分：1)

在VivzAdapter.java中，您将返回null而不是您创建的ViewHolder。

将其更改为

@Override
public MyViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
    View view = inflater.inflate(R.layout.custom_row,parent,false);
    MyViewHolder holder = new MyViewHolder(view);
    return holder;
}

然后它应该工作

答案 1 :(得分：1)

你的VivzAdapter.java返回null，因为它在运行时会抛出空指针异常。

    package com.portal.college.myapplication;

import android.content.Context;
import android.support.v7.widget.RecyclerView;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ImageView;
import android.widget.TextView;

import java.util.Collections;
import java.util.List;

/**
 * Created by admin on 08-Feb-16.
 */
public class VivzAdapter extends RecyclerView.Adapter<VivzAdapter.MyViewHolder>{
    private final LayoutInflater inflater;
    List<Information> data = Collections.emptyList();

    public VivzAdapter(Context context,List<Information> data){
    inflater=LayoutInflater.from(context);
        this.data=data;
}
    @Override
    public MyViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        View view = inflater.inflate(R.layout.custom_row,parent,false);
        MyViewHolder holder = new MyViewHolder(view);
        return holder;
    }


    @Override
    public void onBindViewHolder(MyViewHolder holder, int position) {
Information current = data.get(position);
        holder.title.setText(current.title);
        holder.id.setImageResource(current.iconId);
    }

    @Override
    public int getItemCount() {

            return data.size();

    }
class MyViewHolder extends RecyclerView.ViewHolder{
    TextView title;
    ImageView id;

    public MyViewHolder(View itemView) {
        super(itemView);
        title = (TextView) itemView.findViewById(R.id.listText);
        id = (ImageView) itemView.findViewById(R.id.listIcon);
    }
}
}

上面的代码可能会解决问题。

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