CODEWITHSUNDEEP
androidandroid-viewpagerfragment
Vik0809
Vik0809

Reputation: 379

NullpointerException using ViewPager

I want to have Tabs in my Application and to do so I use the ViewPager but I get this logcat: 

04-17 22:03:31.291  10545-10545/de.gestureanywhere E/AndroidRuntime﹕ FATAL EXCEPTION: main
Process: de.gestureanywhere, PID: 10545
java.lang.NullPointerException
        at android.support.v4.app.BackStackRecord.doAddOp(BackStackRecord.java:416)
        at android.support.v4.app.BackStackRecord.add(BackStackRecord.java:411)
        at android.support.v4.app.FragmentPagerAdapter.instantiateItem(FragmentPagerAdapter.java:99)
        at android.support.v4.view.ViewPager.addNewItem(ViewPager.java:837)
        at android.support.v4.view.ViewPager.populate(ViewPager.java:987)
        at android.support.v4.view.ViewPager.populate(ViewPager.java:919)
        at android.support.v4.view.ViewPager.onMeasure(ViewPager.java:1441)
        at android.view.View.measure(View.java:16514)
        at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5125)
        at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1404)
        at android.widget.LinearLayout.measureVertical(LinearLayout.java:695)
        at android.widget.LinearLayout.onMeasure(LinearLayout.java:588)
        at android.view.View.measure(View.java:16514)
        at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5125)
        at android.widget.FrameLayout.onMeasure(FrameLayout.java:310)
        at android.view.View.measure(View.java:16514)
        at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5125)
        at android.support.v7.internal.widget.ActionBarOverlayLayout.onMeasure(ActionBarOverlayLayout.java:453)
        at android.view.View.measure(View.java:16514)
        at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5125)
        at android.widget.FrameLayout.onMeasure(FrameLayout.java:310)
        at android.view.View.measure(View.java:16514)
        at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5125)
        at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1404)
        at android.widget.LinearLayout.measureVertical(LinearLayout.java:695)
        at android.widget.LinearLayout.onMeasure(LinearLayout.java:588)
        at android.view.View.measure(View.java:16514)
        at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5125)
        at android.widget.FrameLayout.onMeasure(FrameLayout.java:310)
        at com.android.internal.policy.impl.PhoneWindow$DecorView.onMeasure(PhoneWindow.java:2556)
        at android.view.View.measure(View.java:16514)
        at android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:1912)
        at android.view.ViewRootImpl.measureHierarchy(ViewRootImpl.java:1109)
        at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1291)
        at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:996)
        at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:5600)
        at android.view.Choreographer$CallbackRecord.run(Choreographer.java:761)
        at android.view.Choreographer.doCallbacks(Choreographer.java:574)
        at android.view.Choreographer.doFrame(Choreographer.java:544)
        at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:747)
        at android.os.Handler.handleCallback(Handler.java:733)
        at android.os.Handler.dispatchMessage(Handler.java:95)
        at android.os.Looper.loop(Looper.java:136)
        at android.app.ActivityThread.main(ActivityThread.java:5034)
        at java.lang.reflect.Method.invokeNative(Native Method)
        at java.lang.reflect.Method.invoke(Method.java:515)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:795)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:611)
        at dalvik.system.NativeStart.main(Native Method)

Here is my code: 

    public class Vorschlag extends ActionBarActivity implements
        ActionBar.TabListener {

    private ViewPager viewPager;
    private TabsAdapter mAdapter;
    private ActionBar actionBar;

    // Tab titles
    private String[] tabs = { "Neuer Vorschlag", "Vorschläge" };

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        requestWindowFeature(Window.FEATURE_ACTION_BAR);
        super.onCreate(savedInstanceState);



        setContentView(R.layout.vorschlag_layout);

        ActionBar actionBar = getSupportActionBar();

        actionBar.setNavigationMode(ActionBar.NAVIGATION_MODE_LIST);

        actionBar.setDisplayShowTitleEnabled(true);

        mAdapter = new TabsAdapter(getSupportFragmentManager());

        // Initilization
        viewPager = (ViewPager) findViewById(R.id.pager);

       // actionBar = getApplicationContext().getS


        viewPager.setAdapter(mAdapter);



        // Adding Tabs
        for (String tab_name : tabs) {
            actionBar.addTab(actionBar.newTab().setText(tab_name)
                    .setTabListener(this));
        }
    }





    @Override
    public void onTabSelected(ActionBar.Tab tab, android.support.v4.app.FragmentTransaction fragmentTransaction) {

    }

    @Override
    public void onTabUnselected(ActionBar.Tab tab, android.support.v4.app.FragmentTransaction fragmentTransaction) {

    }

    @Override
    public void onTabReselected(ActionBar.Tab tab, android.support.v4.app.FragmentTransaction fragmentTransaction) {

    }
}

this is the layout file: 

<?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
        xmlns:android="http://schemas.android.com/apk/res/android"
        android:id="@+id/pager"
        android:layout_width="match_parent"
        android:layout_height="match_parent">
    </android.support.v4.view.ViewPager>



</LinearLayout>

And here is my Adapter class: 

import android.support.v4.app.FragmentManager;
import android.support.v4.app.FragmentPagerAdapter;


/**
 * Created by Viktor on 17.04.2015.
 */
public class TabsAdapter extends FragmentPagerAdapter {

    public TabsAdapter(FragmentManager fm) {
        super(fm);
    }

    @Override
    public android.support.v4.app.Fragment getItem(int index) {

        switch (index) {
            case 0:
                // Top Rated fragment activity
                // return new TopRatedFragment();
                break;
            case 1:
                // Games fragment activity
                // return new GamesFragment();
                new VorhandeneVorschlaege();
                break;

        }

        return null;
    }

    @Override
    public int getCount() {
        // get item count - equal to number of tabs
        return 2;
    }

}

The Tabs are now displayed thanks. But I have got the problem, that the Tabs are only displayed, when getCount() returns 0. When I return the number of tabs there, the app is terminating. Here is the code:

public class TabsAdapter extends FragmentPagerAdapter {

public TabsAdapter(FragmentManager fm) {

    super(fm);
    Log.d("hier128", "hier128");
}

@Override
public Fragment getItem(int i) {

    Log.d("hier126", "hier126");

    Fragment fragment = null;


    if (i == 0) {
        Log.d("hier130", "hier130");
        fragment = new VorhandeneVorschlaege();
    }


    return fragment;

}



@Override
public int getCount() {
    // get item count - equal to number of tabs
    Log.d("hier129", "hier129");
    return 0;
}

}

And here is the class with the tabs: 

public class Vorschlag extends ActionBarActivity implements
    android.support.v7.app.ActionBar.TabListener {

private ViewPager viewPager;
private TabsAdapter mAdapter;
//private ActionBar actionBar;

// Tab titles
private String[] tabs = { "Neuer Vorschlag", "Vorschläge" };

private android.support.v7.app.ActionBar actionBar;

@Override
protected void onCreate(Bundle savedInstanceState) {

    super.onCreate(savedInstanceState);



    setContentView(R.layout.vorschlag_layout);
    viewPager = (ViewPager) findViewById(R.id.pager);

    FragmentManager fragmnetManager = getSupportFragmentManager();
    actionBar = getSupportActionBar();
    actionBar.setNavigationMode(ActionBar.NAVIGATION_MODE_TABS);

    viewPager.setAdapter(new TabsAdapter(fragmnetManager));
    viewPager.setOnPageChangeListener(new ViewPager.OnPageChangeListener() {

        @Override
        public void onPageSelected(int arg0) {
            // TODO Auto-generated method stub
            actionBar.setSelectedNavigationItem(arg0);
        }

        @Override
        public void onPageScrolled(int arg0, float arg1, int arg2) {
            // TODO Auto-generated method stub

        }

        @Override
        public void onPageScrollStateChanged(int arg0) {
            // TODO Auto-generated method stub

        }
    });


    android.support.v7.app.ActionBar.Tab tab1 = actionBar.newTab();
    tab1.setText("TAB1");
    tab1.setTabListener(this);

    android.support.v7.app.ActionBar.Tab tab2 = actionBar.newTab();
    tab2.setText("TAB2");
    tab2.setTabListener(this);



    actionBar.addTab(tab1);
    actionBar.addTab(tab2);


}

@Override
protected void onSaveInstanceState(Bundle outState) {
    // TODO Auto-generated method stub
    super.onSaveInstanceState(outState);
}

@Override
public boolean onCreateOptionsMenu(Menu menu) {

    // Inflate the menu; this adds items to the action bar if it is present.

    getMenuInflater().inflate(R.menu.menu_gesture_any_where, menu);
    return true;

}


@Override
public void onTabReselected(android.support.v7.app.ActionBar.Tab arg0,
                            FragmentTransaction arg1) {
    // TODO Auto-generated method stub

}

@Override
public void onTabSelected(android.support.v7.app.ActionBar.Tab tab,
                          FragmentTransaction arg1) {
    // TODO Auto-generated method stub
    viewPager.setCurrentItem(tab.getPosition());
}

@Override
public void onTabUnselected(android.support.v7.app.ActionBar.Tab arg0,
                            FragmentTransaction arg1) {
    // TODO Auto-generated method stub

}
}

What is the reason for that?

Thanks

Upvotes: 0

Views: 1313

Answers (2)

Haris Qurashi
Haris Qurashi

Reputation: 2124

You are returning null in adapter's getItem, you are checking the index if it is 0 than you are initializing the fragment. If index other than 0 than returning null, which cause null pointer exception at run time because by default android initialize left/right pages in adapter, if you have more than two fragments

Upvotes: 0

Surender Kumar
Surender Kumar

Reputation: 1123

import android.annotation.TargetApi;
import android.app.ActionBar;
import android.os.Build;
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentManager;
import android.support.v4.app.FragmentPagerAdapter;
import android.support.v4.app.FragmentTransaction;
import android.support.v4.view.ViewPager;
import android.support.v7.app.ActionBarActivity;
import android.view.Menu;

@TargetApi(Build.VERSION_CODES.HONEYCOMB)
public class MainActivity extends ActionBarActivity implements android.support.v7.app.ActionBar.TabListener {
    ViewPager viewPager;
    private android.support.v7.app.ActionBar actionBar;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        viewPager = (ViewPager) findViewById(R.id.pager);
        FragmentManager fragmnetManager = getSupportFragmentManager();
        viewPager.setAdapter(new MyAdapter(fragmnetManager));
        viewPager.setOnPageChangeListener(new ViewPager.OnPageChangeListener() {

            @Override
            public void onPageSelected(int arg0) {
                // TODO Auto-generated method stub
                actionBar.setSelectedNavigationItem(arg0);
            }

            @Override
            public void onPageScrolled(int arg0, float arg1, int arg2) {
                // TODO Auto-generated method stub

            }

            @Override
            public void onPageScrollStateChanged(int arg0) {
                // TODO Auto-generated method stub

            }
        });
        actionBar = getSupportActionBar();
        actionBar.setNavigationMode(ActionBar.NAVIGATION_MODE_TABS);

        android.support.v7.app.ActionBar.Tab tab1 = actionBar.newTab();
        tab1.setText("TAB1");
        tab1.setTabListener(this);

        android.support.v7.app.ActionBar.Tab tab2 = actionBar.newTab();
        tab2.setText("TAB2");
        tab2.setTabListener(this);

        android.support.v7.app.ActionBar.Tab tab3 = actionBar.newTab();
        tab3.setText("TAB3");
        tab3.setTabListener(this);

        actionBar.addTab(tab1);
        actionBar.addTab(tab2);
        actionBar.addTab(tab3);

    }

    @Override
    protected void onSaveInstanceState(Bundle outState) {
        // TODO Auto-generated method stub
        super.onSaveInstanceState(outState);
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {

        // Inflate the menu; this adds items to the action bar if it is present.

        getMenuInflater().inflate(R.menu.main, menu);
        return true;

    }


    @Override
    public void onTabReselected(android.support.v7.app.ActionBar.Tab arg0,
            FragmentTransaction arg1) {
        // TODO Auto-generated method stub

    }

    @Override
    public void onTabSelected(android.support.v7.app.ActionBar.Tab tab,
            FragmentTransaction arg1) {
        // TODO Auto-generated method stub
        viewPager.setCurrentItem(tab.getPosition());
    }

    @Override
    public void onTabUnselected(android.support.v7.app.ActionBar.Tab arg0,
            FragmentTransaction arg1) {
        // TODO Auto-generated method stub

    }

}

class MyAdapter extends FragmentPagerAdapter {
    public MyAdapter(FragmentManager fm) {
        super(fm);

    }

    @Override
    public Fragment getItem(int i) {
        // TODO Auto-generated method stub
        Fragment fragment = null;
        if (i == 0) {
            fragment = new FragmentA();
        }
        if (i == 1) {
            fragment = new FragmentB();
        }
        if (i == 2) {
            fragment = new FragmentC();
        }
        return fragment;
    }

    @Override
    public int getCount() {
        // TODO Auto-generated method stub
        return 3;
    }
}

Upvotes: 1

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