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Editorial Team
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Asked: 2026-06-17T10:31:06+00:00

I’ve been working on this for a week now and I just can’t figure

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I’ve been working on this for a week now and I just can’t figure it out. I have a Pager Adapter with 4 views. It lets me swipe between them. But when I call onClickListener the app crashes on boot because the Listener is null. I’m a new programmer and I don’t understand how I can fix this problem. Please help! I’ve isolated the source of the problem, the view is not created or being destroyed after the Listener looks for the button ID and that’s why it’s null and crashing.

The method destroyItem is what I think is causing it, because when I remove it the app doesn’t crash until I start swiping threw views.

public class SplashPager extends PagerAdapter {

Button b;

@Override
public int getCount() {
    // TODO Auto-generated method stub
    return 4;
}

@Override
public Object instantiateItem(View collection, int position) {
    LayoutInflater inflater = (LayoutInflater) collection.getContext()
            .getSystemService(Context.LAYOUT_INFLATER_SERVICE);

    int resId = 0;
    switch (position) {

    case 0:
        resId = R.layout.splash2;
        b = (Button) collection.findViewById(R.id.splashB);
        b.setOnClickListener(new OnClickListener() {

            @Override
            public void onClick(View v) {
                // TODO Auto-generated method stub
                                    //setContentView(r.layout.someLayout);
            }
        });
        break;
    case 1:
        resId = R.layout.splash3;
        break;
    case 2:
        resId = R.layout.splash4;
        break;
    case 3:
        resId = R.layout.splash5;
        break;

    }

    View view = inflater.inflate(resId, null);
    ((ViewPager) collection).addView(view, 0);
    return view;

}

@Override
public void destroyItem(View arg0, int arg1, Object arg2) {
    // TODO Auto-generated method stub
    ((ViewPager) arg0).removeView((View) arg2);

}

@Override
public Parcelable saveState() {
    // TODO Auto-generated method stub
    return null;
}

@Override
public boolean isViewFromObject(View arg0, Object arg1) {
    // TODO Auto-generated method stub
    return arg0 == ((View) arg1);
}

}

Logs:

01-17 21:03:35.179: W/dalvikvm(16226): threadid=1: thread exiting with uncaught exception (group=0x401a2560)
01-17 21:03:35.179: E/AndroidRuntime(16226): FATAL EXCEPTION: main
01-17 21:03:35.179: E/AndroidRuntime(16226): java.lang.NullPointerException
01-17 21:03:35.179: E/AndroidRuntime(16226):    at   com.example.survtest2.SplashPager.instantiateItem(SplashPager.java:33)
01-17 21:03:35.179: E/AndroidRuntime(16226):    at android.support.v4.view.PagerAdapter.instantiateItem(PagerAdapter.java:110)
01-17 21:03:35.179: E/AndroidRuntime(16226):    at android.support.v4.view.ViewPager.addNewItem(ViewPager.java:801)
01-17 21:03:35.179: E/AndroidRuntime(16226):    at android.support.v4.view.ViewPager.populate(ViewPager.java:930)
01-17 21:03:35.179: E/AndroidRuntime(16226):    at android.support.v4.view.ViewPager.populate(ViewPager.java:881)
01-17 21:03:35.179: E/AndroidRuntime(16226):    at android.support.v4.view.ViewPager.onMeasure(ViewPager.java:1366)
01-17 21:03:35.179: E/AndroidRuntime(16226):    at android.view.View.measure(View.java:8424)
01-17 21:03:35.179: E/AndroidRuntime(16226):    at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:3138)
01-17 21:03:35.179: E/AndroidRuntime(16226):    at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1017)
01-17 21:03:35.179: E/AndroidRuntime(16226):    at android.widget.LinearLayout.measureVertical(LinearLayout.java:386)
01-17 21:03:35.179: E/AndroidRuntime(16226):    at android.widget.LinearLayout.onMeasure(LinearLayout.java:309)
01-17 21:03:35.179: E/AndroidRuntime(16226):    at  android.view.View.measure(View.java:8424)
01-17 21:03:35.179: E/AndroidRuntime(16226):    at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:3138)
01-17 21:03:35.179: E/AndroidRuntime(16226):    at android.widget.FrameLayout.onMeasure(FrameLayout.java:250)
01-17 21:03:35.179: E/AndroidRuntime(16226):    at  android.view.View.measure(View.java:8424)
01-17 21:03:35.179: E/AndroidRuntime(16226):    at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:3138)
01-17 21:03:35.179: E/AndroidRuntime(16226):    at android.widget.FrameLayout.onMeasure(FrameLayout.java:250)
01-17 21:03:35.179: E/AndroidRuntime(16226):    at android.view.View.measure(View.java:8424)
01-17 21:03:35.179: E/AndroidRuntime(16226):    at android.view.ViewRoot.performTraversals(ViewRoot.java:844)
01-17 21:03:35.179: E/AndroidRuntime(16226):    at android.view.ViewRoot.handleMessage(ViewRoot.java:1864)
01-17 21:03:35.179: E/AndroidRuntime(16226):    at android.os.Handler.dispatchMessage(Handler.java:99)
01-17 21:03:35.179: E/AndroidRuntime(16226):    at android.os.Looper.loop(Looper.java:130)
01-17 21:03:35.179: E/AndroidRuntime(16226):    at android.app.ActivityThread.main(ActivityThread.java:3733)
01-17 21:03:35.179: E/AndroidRuntime(16226):    at java.lang.reflect.Method.invokeNative(Native Method)
01-17 21:03:35.179: E/AndroidRuntime(16226):    at java.lang.reflect.Method.invoke(Method.java:507)
01-17 21:03:35.179: E/AndroidRuntime(16226):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:892)
01-17 21:03:35.179: E/AndroidRuntime(16226):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:650)
01-17 21:03:35.179: E/AndroidRuntime(16226):    at dalvik.system.NativeStart.main(Native Method)
01-17 21:03:35.199: E/AndroidRuntime(16226): [Blue Error Handler] Make Debugging Report file for main
01-17 21:03:35.199: E/AndroidRuntime(16226): java.lang.NullPointerException
01-17 21:03:35.199: E/AndroidRuntime(16226):    at com.example.survtest2.SplashPager.instantiateItem(SplashPager.java:33)
01-17 21:03:35.199: E/AndroidRuntime(16226):    at android.support.v4.view.PagerAdapter.instantiateItem(PagerAdapter.java:110)
01-17 21:03:35.199: E/AndroidRuntime(16226):    at android.support.v4.view.ViewPager.addNewItem(ViewPager.java:801)
01-17 21:03:35.199: E/AndroidRuntime(16226):    at android.support.v4.view.ViewPager.populate(ViewPager.java:930)
01-17 21:03:35.199: E/AndroidRuntime(16226):    at android.support.v4.view.ViewPager.populate(ViewPager.java:881)
01-17 21:03:35.199: E/AndroidRuntime(16226):    at android.support.v4.view.ViewPager.onMeasure(ViewPager.java:1366)
01-17 21:03:35.199: E/AndroidRuntime(16226):    at android.view.View.measure(View.java:8424)
01-17 21:03:35.199: E/AndroidRuntime(16226):    at  android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:3138)
01-17 21:03:35.199: E/AndroidRuntime(16226):    at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1017)
01-17 21:03:35.199: E/AndroidRuntime(16226):    at android.widget.LinearLayout.measureVertical(LinearLayout.java:386)
01-17 21:03:35.199: E/AndroidRuntime(16226):    at  android.widget.LinearLayout.onMeasure(LinearLayout.java:309)
01-17 21:03:35.199: E/AndroidRuntime(16226):    at android.view.View.measure(View.java:8424)
01-17 21:03:35.199: E/AndroidRuntime(16226):    at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:3138)
01-17 21:03:35.199: E/AndroidRuntime(16226):    at android.widget.FrameLayout.onMeasure(FrameLayout.java:250)
01-17 21:03:35.199: E/AndroidRuntime(16226):    at android.view.View.measure(View.java:8424)
01-17 21:03:35.199: E/AndroidRuntime(16226):    at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:3138)
01-17 21:03:35.199: E/AndroidRuntime(16226):    at android.widget.FrameLayout.onMeasure(FrameLayout.java:250)
01-17 21:03:35.199: E/AndroidRuntime(16226):    at android.view.View.measure(View.java:8424)
01-17 21:03:35.199: E/AndroidRuntime(16226):    at android.view.ViewRoot.performTraversals(ViewRoot.java:844)
01-17 21:03:35.199: E/AndroidRuntime(16226):    at android.view.ViewRoot.handleMessage(ViewRoot.java:1864)
01-17 21:03:35.199: E/AndroidRuntime(16226):    at android.os.Handler.dispatchMessage(Handler.java:99)
01-17 21:03:35.199: E/AndroidRuntime(16226):    at android.os.Looper.loop(Looper.java:130)
01-17 21:03:35.199: E/AndroidRuntime(16226):    at android.app.ActivityThread.main(ActivityThread.java:3733)
01-17 21:03:35.199: E/AndroidRuntime(16226):    at java.lang.reflect.Method.invokeNative(Native Method)
01-17 21:03:35.199: E/AndroidRuntime(16226):    at    java.lang.reflect.Method.invoke(Method.java:507)
01-17 21:03:35.199: E/AndroidRuntime(16226):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:892)
01-17 21:03:35.199: E/AndroidRuntime(16226):    at    com.android.internal.os.ZygoteInit.main(ZygoteInit.java:650)
01-17 21:03:35.199: E/AndroidRuntime(16226):    at     dalvik.system.NativeStart.main(Native Method)

I’m pretty sure this is the cause of the problem but I don’t know how this method works or how to fix it:

@Override
public void destroyItem(View arg0, int arg1, Object arg2) {
    // TODO Auto-generated method stub
    ((ViewPager) arg0).removeView((View) arg2);

}

Another question I have is how can I use that button to load a new view or activity? It wont allow me to implement activity and that’s the only way I learned how to call in bundles. Thanks in advance!

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1 Answer

  1. Editorial Team

    Try changing destroyItem to this:

    @Override
public void destroyItem(View arg0, int arg1, Object arg2){
    ((ViewPager) arg0).removeViewAt(arg1);
}

    and isViewFromObject to: 

    @Override
public boolean isViewFromObject(View view, Object object){

    return view.equals(object); 
 }

    If these changes dont work then I suggest u check what happens after u can “findViewById” on the collection View. It looks like the button u are looking is not within that object. You have to search for it in the view you are inflating.

    Try this code for your instantiation code:

    @Override
    public Object instantiateItem(View collection, int position) {
        LayoutInflater inflater = (LayoutInflater) collection.getContext()
                .getSystemService(Context.LAYOUT_INFLATER_SERVICE);

        int resId = 0;
        View view = null;
        switch (position) {

        case 0:
            view = inflater.inflate(R.layout.splash2, null);
            b = (Button) view.findViewById(R.id.splashB);
            b.setOnClickListener(new OnClickListener() {

                @Override
                public void onClick(View v) {
                    // TODO Auto-generated method stub
                                        //setContentView(r.layout.someLayout);
                }
            });
            break;
        case 1:
            view = inflater.inflate(R.layout.splash3, null);
            break;
        case 2:
            view = inflater.inflate(R.layout.splash4, null);
            break;
        case 3:
            view = inflater.inflate(R.layout.splash5, null);
            break;

        }


        ((ViewPager) collection).addView(view, 0);
        return view;
    }
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