Android - PagerAdapter crashes when I add a ClickListener

Question

I am implementing an app that uses some horizontal swipe paging (to the left or to the right - Horizontal View Paging). I downloaded “android.support.v4.view.ViewPager” and found the way to implement the swiping part mostly thanks to this tutorial here: http://mobile.tutsplus.com/tutorials/android/android-user-interface-design-horizontal-view-paging/

My problem is to view buttons and set an OnClickListenr in my swiping views. What is strange is that while I can do it within my main activity, it crashes when I try to do it from an other activity that is launched and brought to front.

While the code:

public void Settings(){
    setContentView(R.layout.settings);
    SettingsAdapter adapter = new SettingsAdapter();
    ViewPager myPager = (ViewPager) findViewById(R.id.settingspager);
    myPager.setAdapter(adapter);
    myPager.setCurrentItem(0);      
    View BackButton = findViewById(R.id.back);
    BackButton.setOnClickListener(this);  
}

Works fine in my main activity, the exact same lines crash in “BackButton.setOnClickListener” when used in another activity.

From log I get:

02-20 09:59:50.756: E/AndroidRuntime(489):  at lil.kayak.tabs.Settings$SettingsAdapter.instantiateItem(Settings.java:88)
02-20 09:59:50.756: E/AndroidRuntime(489):  at android.support.v4.view.PagerAdapter.instantiateItem(PagerAdapter.java:110)
02-20 09:59:50.756: E/AndroidRuntime(489):  at android.support.v4.view.ViewPager.addNewItem(ViewPager.java:649)
02-20 09:59:50.756: E/AndroidRuntime(489):  at android.support.v4.view.ViewPager.populate(ViewPager.java:783) 
02-20 09:59:50.756: E/AndroidRuntime(489):  at android.support.v4.view.ViewPager.onMeasure(ViewPager.java:1016)

My pager adapter is in both cases:

private class SettingsAdapter extends PagerAdapter {

    public int getCount() {
        return 2;
    }

    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.settings1;
             break;
        case 1:
            resId = R.layout.settings2;   
            break;
        }

        View view = inflater.inflate(resId, null);

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

        return view;
    }



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

    }

    @Override
    public boolean isViewFromObject(View arg0, Object arg1) {
        return arg0 == ((View) arg1);

    }

    @Override
    public Parcelable saveState() {
        return null;
    }

}

settings.xml is

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent">
<android.support.v4.view.ViewPager
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:id="@+id/settingspager"/>
</LinearLayout>

So what Is the problem? And what should I do to get it work? Thank you in advance!

Edit: I currently worked around it using the android:onClick="Function" in my xml and then

public void Function(View v){}

in my class

It works now but I do not think this is optimal so any proposals are welcome!

Answer 1

maybe the collection isnt a valid view or is simply "null". Better use "getApplicationContext()" or implement a constructor to the adapter that can take the Context from your application.

And, to make sure you have all needed things valid: check the "inflater" against "null", if you dont have a LayoutInflater object, things can crash.

Another reason would be your code outside from this Adapater, this we cant see here ;)