尝试调用虚拟方法.(上下文菜单)..在空对象引用上

Question

您好，我总是会在调试器中遇到此错误，并且该应用程序不会启动。如果我删除上下文menu，它正在工作...

   public class MainActivity extends AppCompatActivity {

public int[] buttonArray = {R.id.button1, R.id.button2, R.id.button3}; // Button Array
public int[] soundsArray = {R.raw.sound1, R.raw.sound2, R.raw.sound3}; // Sound Array

private int[] tabIcons = {
        R.drawable.infoicon,
        R.drawable.soundicon,
        R.drawable.startop
};

int counters=1;
int counter=1;

final int REQ_CODE_EXTERNAL_STORAGE_PERMISSION = 45;
public String ordnerpfad = Environment.getExternalStorageDirectory() + "/Sounds";
public String soundpfad = ordnerpfad + "/sound.mp3";
public File ordnerfile = new File(ordnerpfad);
public File soundfile = new File(soundpfad);
public Uri urisound = Uri.parse(soundpfad);
public byte[] byte1 = new byte [1024];
public int zwischenspeicher = 0;
public InputStream is1;
public FileOutputStream fos;
public Intent teilintent;

InterstitialAd mInterstitialAd;
TabLayout tabLayout;
ViewPager viewPager;
MediaPlayer MainMMP;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    Handler handler1 = new Handler();
    handler1.postDelayed(new Runnable() {
        public void run() {
            requestNewInterstitial();
        }
    }, 14000);
    MobileAds.initialize(getApplicationContext(), "xxxxxxxxxxxxxxx");
    AdView mAdView = (AdView) findViewById(R.id.adView);
    AdRequest request = new AdRequest.Builder()
            .addTestDevice(AdRequest.DEVICE_ID_EMULATOR)        // All emulators
            .addTestDevice("2BB7955A07F972AC2D1DA7617768CE01")
            .build();
    mAdView.loadAd(request);

    mInterstitialAd = new InterstitialAd(this);
    mInterstitialAd.setAdUnitId("xxxxxxxxxxxxxx");
    mInterstitialAd.setAdListener(new AdListener() {
        @Override
        public void onAdLoaded() {
            mInterstitialAd.show();
        }
    });

    for (int i = 0; i < buttonArray.length; i++) {
        Button contextMenuButton = (Button) findViewById(buttonArray[i]);
        registerForContextMenu(contextMenuButton);
    }
    MainMMP = MediaPlayer.create(this, R.raw.sound1);
    viewPager = (ViewPager) findViewById(R.id.viewPager);
    setupViewPager(viewPager);

    tabLayout = (TabLayout) findViewById(R.id.tabLayout);
    tabLayout.setupWithViewPager(viewPager);
    setupTabIcons();
    tabLayout.addOnTabSelectedListener(new TabLayout.OnTabSelectedListener() {
        @Override
        public void onTabSelected(TabLayout.Tab tab) {
            viewPager.setCurrentItem(tab.getPosition());
        }
        @Override
        public void onTabUnselected(TabLayout.Tab tab) {
            viewPager.setCurrentItem(tab.getPosition());
        }
        @Override
        public void onTabReselected(TabLayout.Tab tab) {
            viewPager.setCurrentItem(tab.getPosition());
        }
    });
}

@Override
public void onBackPressed() {
    new AlertDialog.Builder(this)
            .setMessage("Close this App?nnWe are happy for each Feedback :) ")
            .setCancelable(false)
            .setNeutralButton("Rate Us", new    DialogInterface.OnClickListener() {
                public void onClick(DialogInterface dialog, int rate){
                    Intent intent = new Intent();
                    intent.setAction(Intent.ACTION_VIEW);
                    intent.addCategory(Intent.CATEGORY_BROWSABLE);
                    intent.setData(Uri.parse("http...xxxx..xxx"));
                    startActivity(intent);
                }
            })
            .setPositiveButton("Yes", new DialogInterface.OnClickListener() {
                public void onClick(DialogInterface dialog, int id) {
                    MainMMP.release();
                    finish();
                    System.exit(0);
                }
            })
            .setNegativeButton("No", null)
            .show();
}
private void requestNewInterstitial() {
    AdRequest adRequest = new AdRequest.Builder()
            .addTestDevice(AdRequest.DEVICE_ID_EMULATOR)        // All  emulators
            .addTestDevice("2BB7955A07F972AC2D1DA7617768CE01")
            .build();
    mInterstitialAd.loadAd(adRequest);
}
public void Share(View view){
    Intent sendIntent = new Intent();
    sendIntent.setAction(Intent.ACTION_SEND);
    sendIntent.putExtra(Intent.EXTRA_TEXT, "Hey, check this Soundboard");
    sendIntent.setType("text/plain");
    startActivity(sendIntent);
}
@Override
public void onCreateContextMenu(ContextMenu menu, View view, ContextMenu.ContextMenuInfo menuInfo) {
    super.onCreateContextMenu(menu, view, menuInfo);
    menu.setHeaderTitle("Context Menu");
    menu.add(0, view.getId(), 0, "Action 1");
    menu.add(0, view.getId(), 0, "Action 2");
}

@Override
public boolean onContextItemSelected(MenuItem item) {
    if(item.getTitle().equals("Action 1")){function1(item.getItemId());}
    else if(item.getTitle().equals("Action 2")){function2(item.getItemId());}
    else {return false;}
    return true;
}

public void function1(int id){
    for (int i=0; i<buttonArray.length; i++) {
        if (id == buttonArray[i]) {
            if (ActivityCompat.checkSelfPermission(MainActivity.this, Manifest.permission.WRITE_EXTERNAL_STORAGE) == PackageManager.PERMISSION_GRANTED) {

                if (!ordnerfile.exists()) {
                    try {
                        ordnerfile.mkdir();
                        Toast.makeText(getApplicationContext(), "Created Folder", Toast.LENGTH_SHORT).show();
                    } catch (Exception e) {
                        e.printStackTrace();
                        Toast.makeText(getApplicationContext(), "Failed", Toast.LENGTH_SHORT).show();
                    }
                }
                try {

                    is1 = getResources().openRawResource(soundsArray[i]);
                    fos = new FileOutputStream(soundfile);
                    while ((zwischenspeicher = is1.read(byte1)) > 0) {
                        fos.write(byte1, 0, zwischenspeicher);
                    }
                    is1.close();
                    fos.close();
                } catch (Exception e) {
                    e.printStackTrace();
                    Toast.makeText(getApplicationContext(), "Failed", Toast.LENGTH_SHORT).show();
                }
                teilintent = new Intent(Intent.ACTION_SEND);
                teilintent.setType("audio/*");
                teilintent.putExtra(Intent.EXTRA_STREAM, urisound);
                startActivity(Intent.createChooser(teilintent, "Share this Sound..."));
            }
            else {
                ActivityCompat.requestPermissions(MainActivity.this,new String[] {Manifest.permission.WRITE_EXTERNAL_STORAGE}, REQ_CODE_EXTERNAL_STORAGE_PERMISSION);
            }
            return;
        }
    }
}

public void function2(int id){
    Toast.makeText(this, "function 2 called", Toast.LENGTH_SHORT).show();}

public void MainMMP(View view) {

    for (int i=0; i<buttonArray.length; i++) {
        if (view.getId() == buttonArray[i]) {
            MainMMP.release();
            MainMMP = MediaPlayer.create(MainActivity.this, soundsArray[i]);
            MainMMP.start();
        }
    }
}

@Override
public void onRequestPermissionsResult(int requestCode, @NonNull String[] permissions, @NonNull int[] grantResults) {
    super.onRequestPermissionsResult(requestCode, permissions, grantResults);
    if (requestCode == REQ_CODE_EXTERNAL_STORAGE_PERMISSION && grantResults.length >0 && grantResults[0] == PackageManager.PERMISSION_GRANTED) {
        ordnerfile.mkdir();
        Toast.makeText(getApplicationContext(), "Ordner erstellt", Toast.LENGTH_SHORT).show();
    }
}
private void setupTabIcons() {
    tabLayout.getTabAt(0).setIcon(tabIcons[0]);
    tabLayout.getTabAt(1).setIcon(tabIcons[2]);
    tabLayout.getTabAt(2).setIcon(tabIcons[1]);
    tabLayout.getTabAt(3).setIcon(tabIcons[1]);
    tabLayout.getTabAt(4).setIcon(tabIcons[1]);
}
private void setupViewPager(ViewPager viewPager) {
    ViewPagerAdapter adapter = new ViewPagerAdapter(getSupportFragmentManager());
    adapter.addFrag(new FragmentFavourite(), "");
    adapter.addFrag(new Fragment1(), "Top Sounds");
    adapter.addFrag(new Fragment2(), "Sounds 1");
    adapter.addFrag(new Fragment3(), "Sounds 2");
    adapter.addFrag(new Fragment4(), "Sounds 3");
    viewPager.setAdapter(adapter);
}
    class ViewPagerAdapter extends FragmentPagerAdapter {
    private final List<Fragment> mFragmentList = new ArrayList<>();
    private final List<String> mFragmentTitleList = new ArrayList<>();

        private ViewPagerAdapter(FragmentManager manager) {
            super(manager);}
    @Override
    public Fragment getItem(int position) {
        return mFragmentList.get(position);
    }
    @Override
    public int getCount() {
        return mFragmentList.size();
    }
    private void addFrag(Fragment fragment, String title) {
        mFragmentList.add(fragment);
        mFragmentTitleList.add(title);
    }
    @Override
    public CharSequence getPageTitle(int position) {
        return mFragmentTitleList.get(position);
    }
}

}

现在我的tab1.xml实际有更多按钮，但仅对于某些测试，我就使用了第一个3

<?xml version="1.0" encoding="utf-8"?>

<ScrollView
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:fillViewport="true"
    android:layout_alignParentTop="true"
    android:layout_alignParentLeft="true"
    android:layout_alignParentStart="true">

    <TableLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content">
        <TableRow
            android:layout_width="match_parent"
            android:layout_height="match_parent"
              android:layout_gravity="center_vertical|center_horizontal|center"
            android:layout_margin="15dp"
            android:minHeight="90dp">
            <Button
                android:id="@+id/button1"
                android:onClick="MainMMP"
                android:text="Fun FunnFun"
                style="?android:attr/borderlessButtonStyle"
                android:textColor="#FFFFFF"
                android:textSize="20sp"
                android:layout_height="wrap_content"
                android:background="@drawable/mybutton"
                android:layout_marginEnd="15dp"
                android:layout_marginRight="15dp"
                android:layout_weight="1" />

            <Button
                android:id="@+id/button2"
                android:onClick="MainMMP"
                android:text="Sing, Dance,nPretend"
                style="?android:attr/borderlessButtonStyle"
                android:textColor="#FFFFFF"
                android:textSize="20sp"
                android:layout_height="wrap_content"
                android:background="@drawable/mybutton"
                android:layout_weight="1"
                android:layout_marginStart="15dp"
                android:layout_marginLeft="15dp" />
        </TableRow>
        <TableRow
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:layout_margin="15dp"
            android:layout_gravity="center_vertical|center_horizontal|center">
            <Button
                android:id="@+id/button3"
                android:onClick="MainMMP"
                android:text="KazoonSound1"
                style="?android:attr/borderlessButtonStyle"
                android:textColor="#FFFFFF"
                android:textSize="20sp"
                android:layout_height="wrap_content"
                android:background="@drawable/mybutton"
                android:layout_weight="1"
                android:layout_marginEnd="15dp"
                android:layout_marginRight="15dp" />
            <Button
                android:id="@+id/button4"
                android:onClick="MainMMP"
                android:text="Kaaaa-nzooo"
                style="?android:attr/borderlessButtonStyle"
                android:textColor="#FFFFFF"
                android:textSize="20sp"
                android:layout_height="wrap_content"
                android:background="@drawable/mybutton"
                android:layout_weight="1"
                android:layout_marginStart="15dp"
                android:layout_marginLeft="15dp"/>
        </TableRow>
        <TableRow
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:layout_margin="15dp"
            android:layout_gravity="center_vertical|center_horizontal|center">
            <Button
                android:id="@+id/button5"
                android:onClick="MainMMP"
                android:text="KazoonSound2"
                style="?android:attr/borderlessButtonStyle"
                android:textColor="#FFFFFF"
                android:textSize="20sp"
                android:layout_height="wrap_content"
                android:background="@drawable/mybutton"
                android:layout_weight="1"
                android:layout_marginEnd="15dp"
                android:layout_marginRight="15dp"/>
            <Button
                android:id="@+id/button6"
                android:onClick="MainMMP"
                android:text="Just Kazoonit"
                style="?android:attr/borderlessButtonStyle"
                android:textColor="#FFFFFF"
                android:textSize="20sp"
                android:layout_height="wrap_content"
                android:background="@drawable/mybutton"
                android:layout_weight="1"
                android:layout_marginStart="15dp"
                android:layout_marginLeft="15dp"/>
        </TableRow>
        <TableRow
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:layout_margin="15dp"
            android:layout_gravity="center_vertical|center_horizontal|center">
            <Button
                android:id="@+id/button7"
                android:onClick="MainMMP"
                android:text="Special-nfriends"
                style="?android:attr/borderlessButtonStyle"
                android:textColor="#FFFFFF"
                android:textSize="20sp"
                android:layout_height="wrap_content"
                android:background="@drawable/mybutton"
                android:layout_weight="1"
                android:layout_marginEnd="15dp"
                android:layout_marginRight="15dp"/>
            <Button
                android:id="@+id/button8"
                android:onClick="MainMMP"
                android:text="I just n wanna say"
                style="?android:attr/borderlessButtonStyle"
                android:textColor="#FFFFFF"
                android:textSize="20sp"
                android:layout_height="wrap_content"
                android:background="@drawable/mybutton"
                android:layout_weight="1"
                android:layout_marginStart="15dp"
                android:layout_marginLeft="15dp"/>
        </TableRow>
        <TableRow
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:layout_margin="15dp"
            android:layout_gravity="center_vertical|center_horizontal|center">
            <Button
                android:id="@+id/button9"
                android:onClick="MainMMP"
                android:text="Before In met you"
                style="?android:attr/borderlessButtonStyle"
                android:textColor="#FFFFFF"
                android:textSize="20sp"
                android:layout_height="wrap_content"
                android:background="@drawable/mybutton"
                android:layout_weight="1"
                android:layout_marginEnd="15dp"
                android:layout_marginRight="15dp"/>
            <Button
                android:id="@+id/button10"
                android:onClick="MainMMP"
                android:text="Rightn by my side"
                style="?android:attr/borderlessButtonStyle"
                android:textColor="#FFFFFF"
                android:textSize="20sp"
                android:layout_height="wrap_content"
                android:background="@drawable/mybutton"
                android:layout_weight="1"
                android:layout_marginStart="15dp"
                android:layout_marginLeft="15dp"/>
        </TableRow>
        <TableRow
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:layout_margin="15dp"
            android:layout_gravity="center_vertical|center_horizontal|center">
            <Button
                android:id="@+id/button11"
                android:onClick="MainMMP"
                android:text="Sing a Songn for you"
                style="?android:attr/borderlessButtonStyle"
                android:textColor="#FFFFFF"
                android:textSize="20sp"
                android:layout_height="wrap_content"
                android:background="@drawable/mybutton"
                android:layout_weight="1"
                android:layout_marginEnd="15dp"
                android:layout_marginRight="15dp"/>
            <Button
                android:id="@+id/button12"
                android:onClick="MainMMP"
                android:text="Your myn Friend"
                style="?android:attr/borderlessButtonStyle"
                android:textColor="#FFFFFF"
                android:textSize="20sp"
                android:layout_height="wrap_content"
                android:background="@drawable/mybutton"
                android:layout_weight="1"
                android:layout_marginStart="15dp"
                android:layout_marginLeft="15dp"/>
        </TableRow>
        <TableRow
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:layout_margin="15dp"
            android:layout_gravity="center_vertical|center_horizontal|center">
            <Button
                android:id="@+id/button13"
                android:onClick="MainMMP"
                android:text="I was n alone"
                style="?android:attr/borderlessButtonStyle"
                android:textColor="#FFFFFF"
                android:textSize="20sp"
                android:layout_height="wrap_content"
                android:background="@drawable/mybutton"
                android:layout_weight="1"
                android:layout_marginEnd="15dp"
                android:layout_marginRight="15dp"/>
            <Button
                android:id="@+id/button14"
                style="?android:attr/borderlessButtonStyle"
                android:onClick="MainMMP"
                android:text="Lookingn for a friend"
                android:textColor="#FFFFFF"
                android:textSize="20sp"
                android:layout_height="wrap_content"
                android:background="@drawable/mybutton"
                android:layout_weight="1"
                android:layout_marginStart="15dp"
                android:layout_marginLeft="15dp"/>
        </TableRow>
        <TableRow
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:layout_margin="15dp"
            android:layout_gravity="center_vertical|center_horizontal|center">
            <Button
                android:id="@+id/button15"
                android:onClick="MainMMP"
                style="?android:attr/borderlessButtonStyle"
                android:text="Speeeecial-nfrieeeend"
                android:textColor="#FFFFFF"
                android:textSize="20sp"
                android:layout_height="wrap_content"
                android:background="@drawable/mybutton"
                android:layout_weight="1"
                android:layout_marginEnd="15dp"
                android:layout_marginRight="15dp"/>

        </TableRow>
    </TableLayout>
  </ScrollView>

e/androidruntime：致命异常：主过程：com.apsps.someappsa..soundboard，pid：10970 java.lang.runtimeException：无法启动活动componentionInfo {com.apsps.someapsssps.someapsa.someappsa.someappsa.soundboard/com.apspss.someapsps.someapsps.someappsa。activityThread.java:2416）at android.app.activitythread.handlelainchactivity（activityThread.java：2476）at android.app.App.AppivityThread.-Wrap11（activityThread.java）at android.app.app.app.acp.act.act.activitythread.activitythread $ h.handlemessage $ h.handlemessage（activationThread.java：acvationThread.java：activati1344）在android.os.handler.dispatchmessage（handler.java:102）Android.os.looper.loop.loop（looper.java：148）at android.app.activity.AptivityThreadThread.main（activityThread.java：5417）在Java上。lang.reflect.method.invoke（本机方法）com.android.internal.os.zygoteinit $ methodandargscaller.run（zygoteinit.java：726）com.android.introid.intral.internal.os.zygoteinit.zygoteinit.main（zygoteinit.java：661616：61616）由以下原因引起的：java：3227）at com.apsps.someappsa.soundboard.mainactivity.oncreate（mainActivity.java：86）at android.app.app.activity.performitivity.performcreate（activity.java：6237）at android.app.instrument.callactiment.callactivity.callactivity.callactivity.callactivity.callactivityoncroweate.java（java）：1107）at android.app.acptivitythread.performlaunchactactivity（activityThread.java：2369）at android.app.App.App.activityThread.handlelaChneChread.handlelaunchActivity（activityThread.java:2476）at android.app.app.App.AcpitiveTiveTiveTimityThread.ActivityThread.-wrap11（ActiveTh.-Wrap11（activeThRap11）（ActivityThread.java）at androidid。App.ActivityThread $ h.Handlemessage（activityThread.java：1344）at android.os.handler.dispatchmessage（Handler.java:102）at android.java：148 at android.app.App.AptivitivitivitivitivitiveTiveThreadReadReadRead。.os.zygoteinit.main（zygoteinit.java:616）

Answer 1

通过调用FindViewById的指向按钮的代码抛出了零点异常。

Button contextMenuButton = (Button) findViewById(buttanArray[i]);
registerForContextMenu(contextMenuButton);

确保您的按钮[i]具有按钮的正确ID，并且您的XML文件中有一个ID。