How could I fix it? Attempt to invoke virtual method 'void androidx.viewpager.widget.ViewPager.setAdapter on a null object reference

Question

Want do some slides in my app. In the activity the following code works fine, but in the fragments the app crashes and says something like:

java.lang.NullPointerException: Attempt to invoke virtual method 'void android.support.v4.view.ViewPager.setAdapter(android.support.v4.view.PagerAdapter)' on a null object reference How can I fix this?

JAVA

    viewPager = (ViewPager) findViewById(R.id.viewPager);

    sliderDotspanel = (LinearLayout) findViewById(R.id.SliderDots);

    ViewPagerAdapter viewPagerAdapter = new ViewPagerAdapter(this);

    viewPager.setAdapter(viewPagerAdapter); // HERE ERROR

    dotscount = viewPagerAdapter.getCount();
    dots = new ImageView[dotscount];

    for(int i = 0; i < dotscount; i++){

        dots[i] = new ImageView(this);
        dots[i].setImageDrawable(ContextCompat.getDrawable(getApplicationContext(), R.drawable.nonactive_dot));

        LinearLayout.LayoutParams params = new LinearLayout.LayoutParams(LinearLayout.LayoutParams.WRAP_CONTENT, LinearLayout.LayoutParams.WRAP_CONTENT);

        params.setMargins(8, 0, 8, 0);

        sliderDotspanel.addView(dots[i], params);

    }

XML

<android.support.v4.view.ViewPager
    android:id="@+id/viewPager"
    android:layout_width="match_parent"
    android:layout_height="0dp"
    app:layout_constraintBottom_toBottomOf="parent"
    app:layout_constraintTop_toBottomOf="@+id/view2" />

`viewPager` is null. Did you remember to call `setContentView()`? If so, did you do it _before_ the `findViewById()` calls? If yes, then it would seem that there is no `` with ID `viewPager` in the currently loaded layout. — Mike M., Apr 09 '20 at 17:01
It doesn't seem like images would help, in this case. It's purely a code issue. You need to call `setContentView()` with the appropriate `R.layout` before you make those `findViewById()` calls. If you've done that, then, as mentioned above, it would seem like your `ViewPager` is not in that layout. — Mike M., Apr 09 '20 at 17:14
Copy this project from another project that is working, but when migrating to my project this error appeared. My question is how can I solve if this is the same. — Kevinho Morales, Apr 09 '20 at 17:15
I can't give you any more specifics without seeing a [mcve]. At least, the code surrounding that posted, and the relevant layout XML file. — Mike M., Apr 09 '20 at 17:16
Where is your `setContentView()` call? Which `R.layout` are you passing to it? Which layout file is that `` in? — Mike M., Apr 09 '20 at 17:24
That error message is pointing to line 49 in the XML, not your code. We will need to see the complete stack trace; the whole section of red lines around that one. — Mike M., Apr 09 '20 at 17:34

How could I fix it? Attempt to invoke virtual method 'void androidx.viewpager.widget.ViewPager.setAdapter on a null object reference

0 Answers0