CODEWITHSUNDEEP
javaandroidandroid-fragments
user1944429
user1944429

Reputation:

ViewPager & crash, after rotation and swipe, due to a nullpointerexception

So I have a lengthy example, I created just for stack overflow. I can't seem to figure it out. I'm not a native Java programmer so that contributes to some confusion. But, this example requires 10 files, and is not just a code dump.

I've tried debugging this for numerous hours and as a last resort have created as concise of an example as I could of the issue, and have come here for help.

The following are the files, and at the bottom the stack trace. I'm really out of ideas of what to try. It's due to a nullpointerexception, that happens after I rotate the screen then try to slide in the ViewPager. I think should be an easy fix, but it hasn't been so for me.

Below are the java, and xml files, and stack trace. I think they are all necessary because they all are intertwined.

Here is a zip of the files too, if that's useful: https://www.dropbox.com/s/sbv4irar727tp1x/CrashExample.zip?dl=0

main.java

package me.spencernusbaum.crashexample;

import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentActivity;
import android.support.v4.app.FragmentPagerAdapter;
import android.support.v4.view.ViewPager;

import java.util.List;
import java.util.Vector;

/**
 * Created by Spencer on 4/26/2015.
 */
public class main extends FragmentActivity {
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.viewpager);

        ViewPager pager = (ViewPager) findViewById(R.id.viewpager);

        final List<Fragment> fragments = new Vector<Fragment>();

        Fragment f2 = new fragment_view();
        Fragment f1 = fragment_menu.newInstance(f2, pager);
        fragments.add(f1);
        fragments.add(f2);

        pager.setAdapter(new FragmentPagerAdapter(this.getSupportFragmentManager()) {
            @Override
            public Fragment getItem(int i) {
                return fragments.get(i);
            }

            @Override
            public int getCount() {
                return fragments.size();
            }
        });
    }
}

fragment_menu.java

package me.spencernusbaum.crashexample;

import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.support.v4.view.ViewPager;
import android.view.LayoutInflater;
import android.view.MotionEvent;
import android.view.View;
import android.view.ViewGroup;

/**
 * Created by Spencer on 4/26/2015.
 */
public class fragment_menu extends Fragment {

    Fragment fragment;
    ViewPager viewPager;

    public static final fragment_menu newInstance(Fragment f, ViewPager p) {
        fragment_menu result = new fragment_menu();
        result.fragment = f;
        result.viewPager = p;
        return result;
    }

    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        View result = inflater.inflate(R.layout.fragment_menu, null);

        result.findViewById(R.id.button1).setOnTouchListener(new View.OnTouchListener() {
            @Override
            public boolean onTouch(View v, MotionEvent event) {
                ((fragment_view)fragment).setView(new fragment1());
                return false;
            }
        });
        result.findViewById(R.id.button1).setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                ((fragment_view)fragment).setView(new fragment1());
                viewPager.setCurrentItem(1, true);
            }
        });

        result.findViewById(R.id.button2).setOnTouchListener(new View.OnTouchListener() {
            @Override
            public boolean onTouch(View v, MotionEvent event) {
                ((fragment_view)fragment).setView(new fragment2());
                return false;
            }
        });
        result.findViewById(R.id.button2).setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                ((fragment_view)fragment).setView(new fragment2());
                viewPager.setCurrentItem(1, true);
            }
        });

        return result;
    }
}

fragment_view.java

package me.spencernusbaum.crashexample;

import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;

/**
 * Created by Spencer on 4/26/2015.
 */
public class fragment_view extends Fragment {

    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        return inflater.inflate(R.layout.fragment_view, null);
    }

    public void setView(Fragment f) {
        getFragmentManager().beginTransaction().replace(R.id.fragment, f).commit();
    }
}

fragment1.java

package me.spencernusbaum.crashexample;

import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;

/**
 * Created by Spencer on 4/26/2015.
 */
public class fragment1 extends Fragment {

    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        return inflater.inflate(R.layout.fragment1, null);
    }
}

fragment2.java

package me.spencernusbaum.crashexample;

import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;

/**
 * Created by Spencer on 4/26/2015.
 */
public class fragment2 extends Fragment {

    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        return inflater.inflate(R.layout.fragment2, null);
    }
}

fragment1.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical" android:layout_width="match_parent"
    android:layout_height="match_parent">

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:textAppearance="?android:attr/textAppearanceLarge"
        android:text="Fragment1"
        android:id="@+id/textView"
        android:layout_gravity="center_horizontal" />
</LinearLayout>

fragment2.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical" android:layout_width="match_parent"
    android:layout_height="match_parent">

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:textAppearance="?android:attr/textAppearanceLarge"
        android:text="Large Text"
        android:id="@+id/textView2"
        android:layout_gravity="center_horizontal" />
</LinearLayout>

fragment_menu.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical" android:layout_width="match_parent"
    android:layout_height="match_parent">

    <Button
        android:id="@+id/button1"
        android:text="Fragment 1"
        android:layout_weight="1"
        android:layout_width="match_parent"
        android:layout_height="0dp" />

    <Button
        android:id="@+id/button2"
        android:text="Fragment 2"
        android:layout_weight="1"
        android:layout_width="match_parent"
        android:layout_height="0dp" />

</LinearLayout>

fragment_view.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/fragment"
    android:orientation="vertical" android:layout_width="match_parent"
    android:layout_height="match_parent">

</LinearLayout>

viewpager.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical" android:layout_width="match_parent"
    android:layout_height="match_parent">

    <android.support.v4.view.ViewPager
        android:id="@+id/viewpager"
        android:layout_width="match_parent"
        android:layout_height="match_parent" />

</LinearLayout>

The Stack Trace:

04-26 12:38:32.368    7635-7635/me.spencernusbaum.crashexample E/InputEventReceiver﹕ Exception dispatching input event.
        04-26 12:38:32.368    7635-7635/me.spencernusbaum.crashexample E/MessageQueue-JNI﹕ Exception in MessageQueue callback: handleReceiveCallback
        04-26 12:38:32.370    7635-7635/me.spencernusbaum.crashexample E/MessageQueue-JNI﹕ java.lang.NullPointerException: Attempt to invoke virtual method 'void me.spencernusbaum.crashexample.fragment_view.setView(android.support.v4.app.Fragment)' on a null object reference
        at me.spencernusbaum.crashexample.fragment_menu$1.onTouch(fragment_menu.java:32)
        at android.view.View.dispatchTouchEvent(View.java:8382)
        at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2430)
        at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2119)
        at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2430)
        at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2119)
        at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2430)
        at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2119)
        at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2430)
        at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2119)
        at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2430)
        at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2119)
        at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2430)
        at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2119)
        at com.android.internal.policy.impl.PhoneWindow$DecorView.superDispatchTouchEvent(PhoneWindow.java:2314)
        at com.android.internal.policy.impl.PhoneWindow.superDispatchTouchEvent(PhoneWindow.java:1692)
        at android.app.Activity.dispatchTouchEvent(Activity.java:2739)
        at com.android.internal.policy.impl.PhoneWindow$DecorView.dispatchTouchEvent(PhoneWindow.java:2275)
        at android.view.View.dispatchPointerEvent(View.java:8578)
        at android.view.ViewRootImpl$ViewPostImeInputStage.processPointerEvent(ViewRootImpl.java:4021)
        at android.view.ViewRootImpl$ViewPostImeInputStage.onProcess(ViewRootImpl.java:3887)
        at android.view.ViewRootImpl$InputStage.deliver(ViewRootImpl.java:3449)
        at android.view.ViewRootImpl$InputStage.onDeliverToNext(ViewRootImpl.java:3502)
        at android.view.ViewRootImpl$InputStage.forward(ViewRootImpl.java:3468)
        at android.view.ViewRootImpl$AsyncInputStage.forward(ViewRootImpl.java:3578)
        at android.view.ViewRootImpl$InputStage.apply(ViewRootImpl.java:3476)
        at android.view.ViewRootImpl$AsyncInputStage.apply(ViewRootImpl.java:3635)
        at android.view.ViewRootImpl$InputStage.deliver(ViewRootImpl.java:3449)
        at android.view.ViewRootImpl$InputStage.onDeliverToNext(ViewRootImpl.java:3502)
        at android.view.ViewRootImpl$InputStage.forward(ViewRootImpl.java:3468)
        at android.view.ViewRootImpl$InputStage.apply(ViewRootImpl.java:3476)
        at android.view.ViewRootImpl$InputStage.deliver(ViewRootImpl.java:3449)
        at android.view.ViewRootImpl.deliverInputEvent(ViewRootImpl.java:5701)
        at android.view.ViewRootImpl.doProcessInputEvents(ViewRootImpl.java:5675)
        at android.view.ViewRootImpl.enqueueInputEvent(ViewRootImpl.java:5646)
        at android.view.ViewRootImpl$WindowInputEventReceiver.onInputEvent(ViewRootImpl.java:5791)
        at android.view.InputEventReceiver.dispatchInputEvent(InputEventReceiver.java:185)
        at android.os.MessageQueue.nativePollOnce(Native Method)
        at android.os.MessageQueue.next(MessageQueue.java:143)
        at android.os.Looper.loop(Looper.java:122)
        at android.app.ActivityThread.main(ActivityThread.java:5221)
        at java.lang.reflect.Method.invoke(Native Method)
        at java.lang.reflect.Method.invoke(Method.java:372)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)
        04-26 12:38:32.370    7635-7635/me.spencernusbaum.crashexample D/AndroidRuntime﹕ Shutting down VM
        04-26 12:38:32.371    7635-7635/me.spencernusbaum.crashexample E/AndroidRuntime﹕ FATAL EXCEPTION: main
        Process: me.spencernusbaum.crashexample, PID: 7635
        java.lang.NullPointerException: Attempt to invoke virtual method 'void me.spencernusbaum.crashexample.fragment_view.setView(android.support.v4.app.Fragment)' on a null object reference
        at me.spencernusbaum.crashexample.fragment_menu$1.onTouch(fragment_menu.java:32)
        at android.view.View.dispatchTouchEvent(View.java:8382)
        at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2430)
        at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2119)
        at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2430)
        at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2119)
        at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2430)
        at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2119)
        at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2430)
        at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2119)
        at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2430)
        at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2119)
        at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2430)
        at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2119)
        at com.android.internal.policy.impl.PhoneWindow$DecorView.superDispatchTouchEvent(PhoneWindow.java:2314)
        at com.android.internal.policy.impl.PhoneWindow.superDispatchTouchEvent(PhoneWindow.java:1692)
        at android.app.Activity.dispatchTouchEvent(Activity.java:2739)
        at com.android.internal.policy.impl.PhoneWindow$DecorView.dispatchTouchEvent(PhoneWindow.java:2275)
        at android.view.View.dispatchPointerEvent(View.java:8578)
        at android.view.ViewRootImpl$ViewPostImeInputStage.processPointerEvent(ViewRootImpl.java:4021)
        at android.view.ViewRootImpl$ViewPostImeInputStage.onProcess(ViewRootImpl.java:3887)
        at android.view.ViewRootImpl$InputStage.deliver(ViewRootImpl.java:3449)
        at android.view.ViewRootImpl$InputStage.onDeliverToNext(ViewRootImpl.java:3502)
        at android.view.ViewRootImpl$InputStage.forward(ViewRootImpl.java:3468)
        at android.view.ViewRootImpl$AsyncInputStage.forward(ViewRootImpl.java:3578)
        at android.view.ViewRootImpl$InputStage.apply(ViewRootImpl.java:3476)
        at android.view.ViewRootImpl$AsyncInputStage.apply(ViewRootImpl.java:3635)
        at android.view.ViewRootImpl$InputStage.deliver(ViewRootImpl.java:3449)
        at android.view.ViewRootImpl$InputStage.onDeliverToNext(ViewRootImpl.java:3502)
        at android.view.ViewRootImpl$InputStage.forward(ViewRootImpl.java:3468)
        at android.view.ViewRootImpl$InputStage.apply(ViewRootImpl.java:3476)
        at android.view.ViewRootImpl$InputStage.deliver(ViewRootImpl.java:3449)
        at android.view.ViewRootImpl.deliverInputEvent(ViewRootImpl.java:5701)
        at android.view.ViewRootImpl.doProcessInputEvents(ViewRootImpl.java:5675)
        at android.view.ViewRootImpl.enqueueInputEvent(ViewRootImpl.java:5646)
        at android.view.ViewRootImpl$WindowInputEventReceiver.onInputEvent(ViewRootImpl.java:5791)
        at android.view.InputEventReceiver.dispatchInputEvent(InputEventReceiver.java:185)
        at android.os.MessageQueue.nativePollOnce(Native Method)
        at android.os.MessageQueue.next(MessageQueue.java:143)
        at android.os.Looper.loop(Looper.java:122)
        at android.app.ActivityThread.main(ActivityThread.java:5221)
        at java.lang.reflect.Method.invoke(Native Method)
        at java.lang.reflect.Method.invoke(Method.java:372)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)

Upvotes: 0

Views: 1421

Answers (1)

dhke
dhke

Reputation: 15388

When the display is rotated, android (by default) destroys the current activity, including all fragments (the current state of attached fragments and the activity is saved via onSaveInstanceState()).

After the rotate, the activity and attached fragments are re-created (again: by default) and previously saved state is restored (passed as Bundle to onCreate()).

For fragments the android runtime invokes their default, no-arguments constructor.

The newInstance() method of your fragment is never invoked for the re-created fragment, hence your fields are not properly initialized and thus null.

Upvotes: 2

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