空對象引用setAdapter

這是我的代碼： MainActivity：空對象引用setAdapter

package com.example.apekshit.materialdesign; 
import android.support.v4.widget.DrawerLayout; 
import android.support.v7.app.AppCompatActivity; 
import android.os.Bundle; 
import android.support.v7.widget.Toolbar; 
import android.view.Menu; 
import android.view.MenuItem; 

public class MainActivity extends AppCompatActivity { 
    Toolbar toolbar; 

    @Override 
    protected void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     setContentView(R.layout.activity_main); 
     toolbar = (Toolbar) findViewById(R.id.app_bar); 
     setSupportActionBar(toolbar); 
     DrawerLayout dl = (DrawerLayout) findViewById(R.id.drawlayid); 
     Navigationdrawer fragment = (Navigationdrawer) getSupportFragmentManager().findFragmentById(R.id.drawer); 
     fragment.setUp(dl, toolbar); 
     getSupportActionBar().setHomeButtonEnabled(true); 
    } 

    @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); 
    } 
}

片段：

package com.example.apekshit.materialdesign; 

import android.os.Bundle; 
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.support.v7.widget.Toolbar; 
import android.view.LayoutInflater; 
import android.view.View; 
import android.view.ViewGroup; 

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


public class Navigationdrawer extends android.support.v4.app.Fragment { 
    private ActionBarDrawerToggle abdt; 
    private DrawerLayout drawerlayout; 
    RecyclerView rv; 
    myAdapter a; 


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

    @Override 
    public void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 

    } 
    public List<Info> getdata(){ 
     List<Info> list=new ArrayList<>(); 
     String[] titles={"CAT","CATERPILLAR","ELEPHANT","FROG"}; 
     int[] icons={R.drawable.a,R.drawable.b,R.drawable.c,R.drawable.d}; 
     for(int i=0;i<titles.length&&i<icons.length;i++){ 
      Info obj=new Info(); 
      obj.id=icons[i]; 
      obj.text=titles[i]; 
      list.add(obj); 
     } 
     return list; 
    } 

    @Override 
    public View onCreateView(LayoutInflater inflater, ViewGroup container, 
          Bundle savedInstanceState) { 
     // Inflate the layout for this fragment 
     View v=inflater.inflate(R.layout.fragment_navigationdrawer, container, false); 
     rv=(RecyclerView)getActivity().findViewById(R.id.recyclerlist); 


     a=new myAdapter(getActivity(),getdata()); 
     rv.setAdapter(a); 
     rv.setLayoutManager(new LinearLayoutManager(getActivity())); 

     return v; 
    } 


    public void setUp(DrawerLayout dl, final Toolbar toolbar) { 
     drawerlayout = dl; 
     abdt = new ActionBarDrawerToggle(getActivity(), drawerlayout, toolbar, R.string.string_open, R.string.string_close) { 
      @Override 
      public void onDrawerOpened(View drawerView) { 
       super.onDrawerOpened(drawerView); 
       getActivity().invalidateOptionsMenu(); 
      } 

      @Override 
      public void onDrawerSlide(View drawerView, float slideOffset) { 
       if(slideOffset<0.6){ 
        toolbar.setAlpha(1-slideOffset); 
       } 
      } 

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

      } 
     }; 
     drawerlayout.setDrawerListener(abdt); 
     drawerlayout.post(new Runnable() { 
      @Override 
      public void run() { 
       abdt.syncState(); 
      } 
     }); 
    } 


}

適配器類：

package com.example.apekshit.materialdesign; 

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 Apekshit on 07-07-2016. 
*/ 
public class myAdapter extends RecyclerView.Adapter<myAdapter.MyViewHolder>{ 
    LayoutInflater inflater; 
    List<Info> l= Collections.emptyList(); 
    Info info; 
    public myAdapter(Context context, List<Info> Data){ 
     l=Data; 


     inflater = LayoutInflater.from(context); 

    } 


    @Override 
    public MyViewHolder onCreateViewHolder(ViewGroup viewGroup, int i) { 
     View v=inflater.inflate(R.layout.rowlayout,viewGroup,false); 
     MyViewHolder holder=new MyViewHolder(v); 
     return holder; 
    } 

    @Override 
    public void onBindViewHolder(myAdapter.MyViewHolder viewHolder, int i) { 
    info=l.get(i); 
     viewHolder.title.setText(info.text); 
     viewHolder.icon.setImageResource(info.id); 
    } 

    @Override 
    public int getItemCount() { 
     return l.size(); 
    } 
    class MyViewHolder extends RecyclerView.ViewHolder{ 

     TextView title; 
     ImageView icon; 

     public MyViewHolder(View itemView) { 
      super(itemView); 
      title= (TextView) itemView.findViewById(R.id.textView); 
      icon= (ImageView) itemView.findViewById(R.id.imageView); 
     } 
    } 
}

當我啓動應用程序，它崩潰。 logcat的：

07-08 08:40:31.919 27773-27773/? E/AndroidRuntime﹕ FATAL EXCEPTION: main 
    Process: com.example.apekshit.materialdesign, PID: 27773 
    java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.apekshit.materialdesign/com.example.apekshit.materialdesign.MainActivity}: android.view.InflateException: Binary XML file line #24: Error inflating class fragment 
      at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2330) 
      at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2392) 
      at android.app.ActivityThread.access$800(ActivityThread.java:154) 
      at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1308) 
      at android.os.Handler.dispatchMessage(Handler.java:102) 
      at android.os.Looper.loop(Looper.java:135) 
      at android.app.ActivityThread.main(ActivityThread.java:5273) 
      at java.lang.reflect.Method.invoke(Native Method) 
      at java.lang.reflect.Method.invoke(Method.java:372) 
      at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:908) 
      at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:703) 
    Caused by: android.view.InflateException: Binary XML file line #24: Error inflating class fragment 
      at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:767) 
      at android.view.LayoutInflater.rInflate(LayoutInflater.java:810) 
      at android.view.LayoutInflater.rInflate(LayoutInflater.java:813) 
      at android.view.LayoutInflater.inflate(LayoutInflater.java:508) 
      at android.view.LayoutInflater.inflate(LayoutInflater.java:418) 
      at android.view.LayoutInflater.inflate(LayoutInflater.java:365) 
      at android.support.v7.app.AppCompatDelegateImplV7.setContentView(AppCompatDelegateImplV7.java:280) 
      at android.support.v7.app.AppCompatActivity.setContentView(AppCompatActivity.java:140) 
      at com.example.apekshit.materialdesign.MainActivity.onCreate(MainActivity.java:15) 
      at android.app.Activity.performCreate(Activity.java:6041) 
      at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1109) 
      at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2283) 
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2392) 
            at android.app.ActivityThread.access$800(ActivityThread.java:154) 
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1308) 
            at android.os.Handler.dispatchMessage(Handler.java:102) 
            at android.os.Looper.loop(Looper.java:135) 
            at android.app.ActivityThread.main(ActivityThread.java:5273) 
            at java.lang.reflect.Method.invoke(Native Method) 
            at java.lang.reflect.Method.invoke(Method.java:372) 
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:908) 
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:703) 
    Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.support.v7.widget.RecyclerView.setAdapter(android.support.v7.widget.RecyclerView$Adapter)' on a null object reference 
      at com.example.apekshit.materialdesign.Navigationdrawer.onCreateView(Navigationdrawer.java:55) 
      at android.support.v4.app.Fragment.performCreateView(Fragment.java:2074) 
      at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1061) 
      at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1264) 
      at android.support.v4.app.FragmentManagerImpl.addFragment(FragmentManager.java:1366) 
      at android.support.v4.app.FragmentManagerImpl.onCreateView(FragmentManager.java:2409) 
      at android.support.v4.app.FragmentController.onCreateView(FragmentController.java:120) 
      at android.support.v4.app.FragmentActivity.dispatchFragmentsOnCreateView(FragmentActivity.java:374) 
      at android.support.v4.app.BaseFragmentActivityHoneycomb.onCreateView(BaseFragmentActivityHoneycomb.java:33) 
      at android.support.v4.app.FragmentActivity.onCreateView(FragmentActivity.java:75) 
      at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:737) 
            at android.view.LayoutInflater.rInflate(LayoutInflater.java:810) 
            at android.view.LayoutInflater.rInflate(LayoutInflater.java:813) 
            at android.view.LayoutInflater.inflate(LayoutInflater.java:508) 
            at android.view.LayoutInflater.inflate(LayoutInflater.java:418) 
            at android.view.LayoutInflater.inflate(LayoutInflater.java:365) 
            at android.support.v7.app.AppCompatDelegateImplV7.setContentView(AppCompatDelegateImplV7.java:280) 
            at android.support.v7.app.AppCompatActivity.setContentView(AppCompatActivity.java:140) 
            at com.example.apekshit.materialdesign.MainActivity.onCreate(MainActivity.java:15) 
            at android.app.Activity.performCreate(Activity.java:6041) 
            at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1109) 
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2283) 
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2392) 
            at android.app.ActivityThread.access$800(ActivityThread.java:154) 
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1308) 
            at android.os.Handler.dispatchMessage(Handler.java:102) 
            at android.os.Looper.loop(Looper.java:135) 
            at android.app.ActivityThread.main(ActivityThread.java:5273) 
            at java.lang.reflect.Method.invoke(Native Method) 
            at java.lang.reflect.Method.invoke(Method.java:372) 
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:908) 
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:703)

fragment_navigationdrawer.xml：

<RelativeLayout 
    xmlns:android="http://schemas.android.com/apk/res/android" 
    android:layout_width="240dp" 
    android:layout_height="match_parent"> 

    <TextView 
     android:id="@+id/tv" 
     android:layout_width="match_parent" 
     android:layout_height="150dp" 
     android:background="#7C6C77" 
     android:gravity="center_horizontal|center_vertical" 
     android:text="Apekshit Tewathia" 

     android:textColor="#FFF" /> 

    <android.support.v7.widget.RecyclerView 
     android:layout_width="match_parent" 
    android:layout_height="wrap_content" 
    android:id="@+id/recyclerlist"> 

</android.support.v7.widget.RecyclerView></RelativeLayout>

activity_main.xml中：

<LinearLayout 
    android:layout_width="match_parent" 
    android:layout_height="match_parent" 
    android:orientation="vertical" 
    android:fitsSystemWindows="true" 
    xmlns:android="http://schemas.android.com/apk/res/android"> 
<include android:id="@+id/app_bar" 
    layout="@layout/app_bar"/> 

<android.support.v4.widget.DrawerLayout 
    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:id="@+id/drawlayid"> 

    <RelativeLayout 
     android:layout_width="match_parent" 
     android:layout_height="match_parent" 
/> 


    <fragment 
     android:id="@+id/drawer" 
     android:layout_width="240dp" 
     android:layout_height="match_parent" 
     android:layout_gravity="start" 
     class="com.example.apekshit.materialdesign.Navigationdrawer" 
     tools:layout="@layout/fragment_navigationdrawer" 
     app:layout="@layout/fragment_navigationdrawer"/> 

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

請幫我code.I用Google搜索了很多，我似乎並沒有找到任何解決方案。預先感謝:) 此外，這是我的第一個問題，所以告訴我，如果我沒有正確發佈問題，並建議我請我如何發佈e問題以更好的方式。謝謝我看了解nullpointerexplanation的不同解釋，仍然無法找到我的代碼中出了什麼問題。這就是爲什麼我在這裏發佈。我的問題的問題被標記爲重複的，因爲不足以解釋我解決了這個問題

來源

2016-07-08 Apekshit Tewathia

您需要setLayoutManager之前setAdapter之前first。 second在您的佈局文件中有錯誤fragment_navigationdrawer行。

rv=(RecyclerView)getActivity().findViewById(R.id.recyclerlist);

應該

rv=(RecyclerView)v.findViewById(R.id.recyclerlist);

這裏，因爲活動前該onCreateView調用創建使getActivity()返回null。

來源

2016-07-08 03:22:45 phongvan

交換setAdapter和setLayoutManager的poaitions已將set set adapter的null指針異常更改爲setLayoutManager方法。並且我在佈局文件中似乎沒有發現任何錯誤。 –

二進制XML文件行＃24：錯誤的擴展類片段，請顯示xml文件 – phongvan

我已經在問題中添加了xml文件。請看看 –

空對象引用setAdapter

回答

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