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Android 尝试调用虚拟方法'；Bundle.getParcelableArrayList（java.lang.String）和#x27；关于空对象引用

android listview android-fragments android-studio

Android 尝试调用虚拟方法'；Bundle.getParcelableArrayList（java.lang.String）和#x27；关于空对象引用,android,listview,android-fragments,android-studio,android-mediaplayer,Android,Listview,Android Fragments,Android Studio,Android Mediaplayer,我有两个片段。从一个片段中我选择歌曲，从另一个片段中我播放歌曲。但当我试图运行它时，我得到了runtimeException 片段current_song.java的代码： package com.example.mandar.mediaplayer; import android.content.Context; import android.content.Intent; import android.media.MediaPlayer; import android.net.Uri; i

我有两个片段。从一个片段中我选择歌曲，从另一个片段中我播放歌曲。但当我试图运行它时，我得到了runtimeException

片段current_song.java的代码：

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;
}


}
用于启动活动的意图不包含额外内容，因此
getExtras（）
返回
null
。您应该编写相应的代码来处理此类情况，如果这不是活动的有效状态，您也可以自己抛出异常（在这种情况下，您需要确保您只是出于有适当额外内容的目的启动活动）。

好的，谢谢，我添加了try-catch。但是，当我使用intent在两个片段之间切换时，代码是否正确？如果不是的话，我该如何处理并将所有（额外的）数据从一个片段传递到另一个片段？@maddy在尝试从包中读取值之前，最好先检查包是否为null（
b！=null
）。我不知道你剩下的代码是怎么工作的。如果你遇到其他问题，你应该问新问题，而不是试图复合这个问题。 
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;
}

}

<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>

<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>

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)