从一个片段移动到另一个片段时，应用程序崩溃

Question

I have four fragments in my application. the first one gets GPS data for calculating speed which works fine. as soon as the application gets the gps data and move to other fragments it crashes. FYI, other fragments are all without any code.

here is my MainActivity class:

 package ir.helpx.speedx; import android.Manifest; import android.content.pm.ActivityInfo; import android.content.pm.PackageManager; import android.os.Build; import android.support.design.widget.TabLayout; import android.support.v4.app.ActivityCompat; import android.support.v4.content.ContextCompat; import android.support.v4.view.ViewPager; import android.support.v7.app.AppCompatActivity; import android.os.Bundle; import android.support.v7.widget.Toolbar; import android.view.WindowManager; import android.widget.Toast; public class MainActivity extends AppCompatActivity { Toolbar toolbar; TabLayout tabLayout; ViewPager viewPager; ViewPagerAdapter viewPagerAdapter; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); toolbar =(Toolbar)findViewById(R.id.toolBar); setSupportActionBar(toolbar); tabLayout = (TabLayout) findViewById(R.id.tabLayout); viewPager = (ViewPager) findViewById(R.id.viewPager); viewPagerAdapter = new ViewPagerAdapter(getSupportFragmentManager()); viewPagerAdapter.addFragments(new HomeFragment(), "Home"); viewPagerAdapter.addFragments(new CompassFragment(), "Compass"); viewPagerAdapter.addFragments(new HUDFragment(), "HUD"); viewPager.setAdapter(viewPagerAdapter); tabLayout.setupWithViewPager(viewPager); getWindow().addFlags(WindowManager.LayoutParams.FLAG_KEEP_SCREEN_ON); setRequestedOrientation (ActivityInfo.SCREEN_ORIENTATION_PORTRAIT); if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) { ActivityCompat.requestPermissions(this, new String[]{android.Manifest.permission.ACCESS_FINE_LOCATION}, 1); } } @Override public void onRequestPermissionsResult(int requestCode, String permissions[], int[] grantResults) { switch (requestCode) { case 1: if (grantResults.length > 0 && grantResults[0] == PackageManager.PERMISSION_GRANTED) { Toast.makeText(this,"GPS permission granted", Toast.LENGTH_LONG).show(); // get Location from your device by some method or code } else { // show user that permission was denied. inactive the location based feature or force user to close the app } break; } } } 

and my MainActivity XML:

 <?xml version="1.0" encoding="utf-8"?> <android.support.constraint.ConstraintLayout 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" tools:context="ir.helpx.speedx.MainActivity"> <android.support.design.widget.AppBarLayout android:layout_height="wrap_content" android:layout_width="368dp" tools:layout_editor_absoluteY="0dp" tools:layout_editor_absoluteX="8dp" android:theme="@style/ThemeOverlay.AppCompat.Dark.ActionBar"> <include android:layout_height="wrap_content" android:layout_width="match_parent" layout="@layout/toolbar_layout" /> <android.support.design.widget.TabLayout android:layout_width="match_parent" android:layout_height="wrap_content" android:id="@+id/tabLayout" app:tabMode="fixed" app:tabGravity="fill" ></android.support.design.widget.TabLayout> <android.support.v4.view.ViewPager android:layout_width="match_parent" android:layout_height="wrap_content" android:id="@+id/viewPager" ></android.support.v4.view.ViewPager> </android.support.design.widget.AppBarLayout> </android.support.constraint.ConstraintLayout> 

and here is my first Fragment called Home:

 package ir.helpx.speedx; import android.location.Location; import android.location.LocationListener; import android.location.LocationManager; import android.os.Bundle; import android.support.v4.app.Fragment; import android.view.LayoutInflater; import android.view.View; import android.view.ViewGroup; import android.widget.TextView; import android.widget.Toast; /** * A simple {@link Fragment} subclass. */ public class HomeFragment extends Fragment implements LocationListener{ public HomeFragment() { // Required empty public constructor } @Override public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) { // Inflate the layout for this fragment LocationManager mgr; mgr = (LocationManager)getContext().getSystemService(getActivity().LOCATION_SERVICE); mgr.requestLocationUpdates(LocationManager.GPS_PROVIDER, 0, 0, this); this.onLocationChanged(null); return inflater.inflate(R.layout.fragment_home, container, false); } //TextView msg1; @Override public void onLocationChanged(Location location) { if (location==null){ TextView currentSpeed = null; } else { float nCurrentSpeed = location.getSpeed(); TextView currentSpeed = (TextView) getView().findViewById(R.id.speed); currentSpeed.setText((int)nCurrentSpeed*18/5+""); //msg1=currentSpeed; Toast.makeText(getActivity(), "Location Found!", Toast.LENGTH_LONG).show(); } } @Override public void onStatusChanged(String provider, int status, Bundle extras) { } @Override public void onProviderEnabled(String provider) { } @Override public void onProviderDisabled(String provider) { } } 

and here is the related XML

 <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="ir.helpx.speedx.HomeFragment"> <!-- TODO: Update blank fragment layout --> <TextView android:layout_width="match_parent" android:layout_height="match_parent" android:text="@string/speed" android:gravity="center" android:textSize="180sp" android:textStyle="bold" android:textColor="@android:color/white" android:id="@+id/speed"/> </FrameLayout> 

and here is my second Fragment:

 package ir.helpx.speedx; import android.os.Bundle; import android.support.v4.app.Fragment; import android.view.LayoutInflater; import android.view.View; import android.view.ViewGroup; /** * A simple {@link Fragment} subclass. */ public class HUDFragment extends Fragment { public HUDFragment() { // Required empty public constructor } @Override public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) { // Inflate the layout for this fragment return inflater.inflate(R.layout.fragment_hud, container, false); } } 

rest of the fragments are similar to

I have a toolbar XML:

 <?xml version="1.0" encoding="utf-8"?> <android.support.v7.widget.Toolbar xmlns:app="http://schemas.android.com/apk/res-auto" xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="match_parent" android:layout_height="wrap_content" android:background="?attr/colorPrimary" android:minWidth="?attr/actionBarSize" android:fitsSystemWindows="true" android:id="@+id/toolBar" android:theme="@style/ThemeOverlay.AppCompat.Dark.ActionBar" > </android.support.v7.widget.Toolbar> 

and finally my my ViewPagerAdapter:

 package ir.helpx.speedx; import android.support.v4.app.Fragment; import android.support.v4.app.FragmentManager; import android.support.v4.app.FragmentPagerAdapter; import android.support.v4.view.ViewPager; import java.util.ArrayList; /** * Created by abe on 5/29/2017. */ public class ViewPagerAdapter extends FragmentPagerAdapter { ArrayList<Fragment> fragments = new ArrayList<>(); ArrayList<String> tabTitles = new ArrayList<>(); public void addFragments(Fragment fragments, String titles){ this.fragments.add(fragments); this.tabTitles.add(titles); } public ViewPagerAdapter(FragmentManager fm){ super(fm); } @Override public Fragment getItem(int position) { return fragments.get(position); } @Override public int getCount() { return fragments.size(); } @Override public CharSequence getPageTitle(int position) { return tabTitles.get(position); } } 

Please HELP me! thank you

Answer 1

I think I could fix it by adding

 viewPager.setOffscreenPageLimit(4); 

to my MainActivity. I think that was because by default ViewPager retains only one page in the view hierarchy in an idle state. Please tell me if I did the right thing!