ヌルオブジェクトリファレンスで仮想メソッド 'Bundle.getParcelableArrayList（java.lang.String）'を呼び出そうとしています

Question

私はMainActivityを二つのフラグメントを管理しています。一つは私が選んだ曲、もう一つは演奏しています。しかし、私はそれを実行しようとしているときに私はruntimeExceptionを取得しています。フラグメントcurrent_song.javaため

コード：フラグメントsongs.javaため

package com.example.mandar.mediaplayer; 

import android.content.Context; 
import android.content.Intent; 
import android.media.MediaPlayer; 
import android.net.Uri; 
import android.os.Bundle; 
import android.support.v4.app.Fragment; 
import android.view.LayoutInflater; 
import android.view.View; 
import android.view.ViewGroup; 

import java.io.File; 
import java.util.ArrayList; 


public class current_song extends Fragment { 
MediaPlayer mp; 
ArrayList<File> mySongs; 


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


@Override 
public View onCreateView(LayoutInflater inflater, ViewGroup container, 
         Bundle savedInstanceState) { 
    // Inflate the layout for this fragment 
    View view= inflater.inflate(R.layout.fragment_current_song, container, false); 

    Intent i=getActivity().getIntent(); 
    Bundle b=i.getExtras(); 

    mySongs= (ArrayList) b.getParcelableArrayList("songlist"); 
    int position = b.getInt("pos",0); 

    Uri u= Uri.parse(mySongs.get(position).toString()); 
    mp= MediaPlayer.create(getActivity().getApplicationContext(),u); 
    mp.start(); 


    return view; 
} 


} 

コード：fragment_songs.xml

ため

<FrameLayout 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" 
    tools:context="com.example.mandar.mediaplayer.current_song"> 

    <!-- TODO: Update blank fragment layout --> 
    <RelativeLayout 
     android:layout_width="match_parent" 
     android:layout_height="wrap_content" 
     android:layout_gravity="center_horizontal|top"> 

     <ImageView 
      android:layout_width="wrap_content" 
      android:layout_height="wrap_content" 
      android:id="@+id/imageView" 
      android:src="@drawable/abc" 
      android:layout_alignParentTop="true" 
      android:layout_centerHorizontal="true" 
      android:layout_marginTop="119dp" /> 

     <TextView 
      android:layout_width="wrap_content" 
      android:layout_height="wrap_content" 
      android:textAppearance="?android:attr/textAppearanceLarge" 
      android:text="Media Player" 
      android:id="@+id/textview" 
      android:layout_marginTop="61dp" 
      android:layout_alignParentTop="true" 
      android:layout_centerHorizontal="true" /> 


     <Button 
      android:layout_width="wrap_content" 
      android:layout_height="wrap_content" 

      android:id="@+id/button" 
      android:text="&lt;&lt;" 
      android:width="70dp" 
      android:height="40dp" 
      android:layout_alignBaseline="@+id/button2" 
      android:layout_alignBottom="@+id/button2" 
      android:layout_toLeftOf="@+id/button2" 
      android:layout_toStartOf="@+id/button2" /> 

     <Button 
      android:layout_width="wrap_content" 
      android:layout_height="wrap_content" 
      android:text="||" 
      android:id="@+id/button2" 
      android:width="70dp" 
      android:height="40dp" 
      android:layout_below="@+id/seekBar" 
      android:layout_alignLeft="@+id/imageView" 
      android:layout_alignStart="@+id/imageView" /> 

     <Button 
      android:layout_width="wrap_content" 
      android:layout_height="wrap_content" 
      android:width="70dp" 
      android:height="40dp" 
      android:id="@+id/button3" 
      android:layout_alignTop="@+id/button" 
      android:layout_toRightOf="@+id/button2" 
      android:layout_toEndOf="@+id/button2" 
      android:text=">" /> 

     <Button 
      android:layout_width="wrap_content" 
      android:layout_height="wrap_content" 

      android:id="@+id/button4" 
      android:text=">>" 
      android:width="70dp" 
      android:height="40dp" 
      android:layout_below="@+id/seekBar" 
      android:layout_toRightOf="@+id/button3" 
      android:layout_alignParentRight="true" 
      android:layout_alignParentEnd="true" /> 

     <SeekBar 
      android:layout_width="wrap_content" 
      android:layout_height="wrap_content" 
      android:id="@+id/seekBar" 

      android:layout_below="@+id/textView2" 
      android:layout_alignParentLeft="true" 
      android:layout_alignParentStart="true" 
      android:layout_marginTop="25dp" 
      android:layout_alignParentRight="true" 
      android:layout_alignParentEnd="true" /> 

     <TextView 
      android:layout_width="wrap_content" 
      android:layout_height="wrap_content" 
      android:textAppearance="?android:attr/textAppearanceSmall" 
      android:text="Small Text" 
      android:id="@+id/textView2" 
      android:layout_marginTop="34dp" 
      android:layout_below="@+id/imageView" 
      android:layout_alignParentLeft="true" 
      android:layout_alignParentStart="true" /> 

     <TextView 
      android:layout_width="wrap_content" 
      android:layout_height="wrap_content" 
      android:textAppearance="?android:attr/textAppearanceSmall" 
      android:text="Small Text" 
      android:id="@+id/textView3" 
      android:layout_alignBottom="@+id/textView4" 
      android:layout_alignParentRight="true" 
      android:layout_alignParentEnd="true" /> 

     <TextView 
      android:layout_width="wrap_content" 
      android:layout_height="wrap_content" 
      android:textAppearance="?android:attr/textAppearanceMedium" 
      android:text="Medium Text" 
      android:id="@+id/textView4" 

      android:layout_alignBottom="@+id/textView2" 
      android:layout_alignLeft="@+id/textview" 
      android:layout_alignStart="@+id/textview" /> 

    </RelativeLayout> 


</FrameLayout> 

コードfragment_current_song.xmlため

public class songs extends ListFragment { 
String(String.valueOf(Environment.getExternalStorageDirectory())); 
ListView lv; 
String[] items; 

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


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





} 

@Override 
public View onCreateView(LayoutInflater inflater, ViewGroup container, 
         Bundle savedInstanceState) { 

    // Inflate the layout for this fragment 



    return inflater.inflate(R.layout.fragment_songs, container, false); 


} 

@Override 
public void onViewCreated (View view, Bundle savedInstanceState) { 
lv=getListView(); 
    // lv = (ListView)view.findViewById(R.id.list); 
    final ArrayList<File> mysongs =findsongs(Environment.getExternalStorageDirectory()); 
    items =new String[ mysongs.size()]; 

    for (int i=0; i<mysongs.size(); i++){ 

     //toast(mysongs.get(i).getName().toString()); 
     items[i]=mysongs.get(i).getName().toString().replace(".mp3",""); 
    } 

    ArrayAdapter<String> adp = new ArrayAdapter<String>(getActivity().getApplicationContext(),R.layout.song_item,R.id.text1,items); 
    lv.setAdapter(adp); 
    lv.setOnItemClickListener(new AdapterView.OnItemClickListener() { 
     @Override 
     public void onItemClick(AdapterView<?> parent, View view, int position, long id) { 

      startActivity(new Intent(getActivity().getApplicationContext(),current_song.class).putExtra("pos",position).putExtra("songlist",mysongs)); 

     } 
    }); 




} 


public void toast (String text){ 
    Toast.makeText(getActivity().getApplicationContext(),text,Toast.LENGTH_SHORT).show(); 


} 

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



} 

    public ArrayList<File> findsongs(File root){ 
    ArrayList<File> a1=new ArrayList<File>(); 
    File[] files=root.listFiles(); 
    for (File singleFile : files){ 
     if(singleFile.isDirectory() && !singleFile.isHidden()){ 
      a1.addAll(findsongs(singleFile)); 

     } 
     else { 
      if (singleFile.getName().endsWith(".mp3") || singleFile.getName().endsWith(".wav")){ 
       a1.add(singleFile); 
      } 
     } 
    } 
    return a1; 
} 

} 

コード

<FrameLayout 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" 
    tools:context="com.example.mandar.mediaplayer.songs"> 

    <!-- TODO: Update blank fragment layout --> 


    <ListView 
     android:layout_width="wrap_content" 
     android:layout_height="440dp" 
     android:id="@android:id/list" 
     android:layout_gravity="center_horizontal|top" /> 
</FrameLayout> 

エラーログ：

04-17 22:20:34.035 26799-26799/com.example.mandar.mediaplayer E/AndroidRuntime: FATAL EXCEPTION: main 
                      Process: com.example.mandar.mediaplayer, PID: 26799 
                      java.lang.NullPointerException: Attempt to invoke virtual method 'java.util.ArrayList android.os.Bundle.getParcelableArrayList(java.lang.String)' on a null object reference 
                       at com.example.mandar.mediaplayer.current_song.onCreateView(current_song.java:36) 
                       at android.support.v4.app.Fragment.performCreateView(Fragment.java:1974) 
                       at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1067) 
                       at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1252) 
                       at android.support.v4.app.BackStackRecord.run(BackStackRecord.java:738) 
                       at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1617) 
                       at android.support.v4.app.FragmentManagerImpl.executePendingTransactions(FragmentManager.java:570) 
                       at android.support.v4.app.FragmentPagerAdapter.finishUpdate(FragmentPagerAdapter.java:141) 
                       at android.support.v4.view.ViewPager.populate(ViewPager.java:1177) 
                       at android.support.v4.view.ViewPager.populate(ViewPager.java:1025) 
                       at android.support.v4.view.ViewPager.onMeasure(ViewPager.java:1545) 
                       at android.view.View.measure(View.java:17637) 
                       at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5536) 
                       at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1436) 
                       at android.widget.LinearLayout.measureVertical(LinearLayout.java:722) 
                       at android.widget.LinearLayout.onMeasure(LinearLayout.java:613) 
                       at android.support.design.widget.AppBarLayout.onMeasure(AppBarLayout.java:199) 
                       at android.view.View.measure(View.java:17637) 
                       at android.widget.RelativeLayout.measureChildHorizontal(RelativeLayout.java:728) 
                       at android.widget.RelativeLayout.onMeasure(RelativeLayout.java:464) 
                       at android.view.View.measure(View.java:17637) 
                       at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5536) 
                       at android.widget.FrameLayout.onMeasure(FrameLayout.java:436) 
                       at android.support.v7.widget.ContentFrameLayout.onMeasure(ContentFrameLayout.java:135) 
                       at android.view.View.measure(View.java:17637) 
                       at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5536) 
                       at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1436) 
                       at android.widget.LinearLayout.measureVertical(LinearLayout.java:722) 
                       at android.widget.LinearLayout.onMeasure(LinearLayout.java:613) 
                       at android.view.View.measure(View.java:17637) 
                       at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5536) 
                       at android.widget.FrameLayout.onMeasure(FrameLayout.java:436) 
                       at android.view.View.measure(View.java:17637) 
                       at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5536) 
                       at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1436) 
                       at android.widget.LinearLayout.measureVertical(LinearLayout.java:722) 
                       at android.widget.LinearLayout.onMeasure(LinearLayout.java:613) 
                       at android.view.View.measure(View.java:17637) 
                       at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5536) 
                       at android.widget.FrameLayout.onMeasure(FrameLayout.java:436) 
                       at com.android.internal.policy.impl.PhoneWindow$DecorView.onMeasure(PhoneWindow.java:2618) 
                       at android.view.View.measure(View.java:17637) 
                       at android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:2019) 
                       at android.view.ViewRootImpl.measureHierarchy(ViewRootImpl.java:1177) 
                       at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1383) 
                       at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1065) 
                       at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:5901) 
                       at android.view.Choreographer$CallbackRecord.run(Choreographer.java:767) 
                       at android.view.Choreographer.doCallbacks(Choreographer.java:580) 
                       at android.view.Choreographer.doFrame(Choreographer.java:550) 
                       at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:753) 
                       at android.os.Handler.handleCallback(Handler.java:739) 
                       at android.os.Handler.dispatchMessage(Handler.java:95) 
                       at android.os.Looper.loop(Looper.java:211) 
                       at android.app.ActivityThread.main(ActivityThread.java:5389) 

Answer 1

あなたの活動を開始するために使用されるテントにはエキストラが含まれていないので、getExtras()戻りnull。このようなケースを適切に処理するコードを記述するか、これがアクティビティの有効な状態でない場合は例外をスローする必要があります（この場合は、適切なエクストラを持つインテントでアクティビティを開始する必要があります） 。