尝试调用虚方法 - 空对象引用

Question

I am trying to implement an external colorwheel and the fragment where it should appear in keeps crashing my app. I think I understood why this happen´s, but after around 6 hours of trying to fix it I´m about to give up. I know this was asked befor, but I could not derive a fix for my specific problem. Here ist my code:

    private ColorchoiceViewModel galleryViewModel;


    public View onCreateView(@NonNull LayoutInflater inflater,
                             ViewGroup container, Bundle savedInstanceState) {
        galleryViewModel =
                ViewModelProviders.of(this).get(ColorchoiceViewModel.class);
        View root = inflater.inflate(R.layout.fragment_colorchoice, container, false);

        galleryViewModel.getText().observe(getViewLifecycleOwner(), new Observer<String>() {
            @Override
            public void onChanged(@Nullable String s) {
            }
        });



        ColorPickerView colorPickerView = (ColorPickerView) root.findViewById(R.id.colorPickerView);
        colorPickerView.setColorListener (new ColorListener() {
            @Override
            public void onColorSelected(ColorEnvelope colorEnvelope) {
                Toast.makeText(getActivity(), "Color:" + colorEnvelope.getColorRGB(), Toast.LENGTH_SHORT).show();
            }
        });



        return root;
    }
}

And this is the Logcat-Error:

java.lang.NullPointerException: Attempt to invoke virtual method 'void com.skydoves.colorpickerpreference.ColorPickerView.setColorListener(com.skydoves.colorpickerpreference.ColorListener)' on a null object reference
        at com.lsh.homeauto.ui.colorchoice.ColorchoiceFragment.onCreateView(ColorchoiceFragment.java:43)

It would be really great if someone could help me fix this. Thanks in advance^^

Edit: Here´s my XML, as requested:

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:paddingLeft="16dp"
    android:paddingRight="16dp"
    android:orientation="horizontal"
    android:gravity="center">

    <com.skydoves.colorpickerpreference.ColorPickerView
        android:id="@+id/colorPickerView"
        android:layout_width="300dp"
        android:layout_height="300dp"
        app:palette="@drawable/palette"
        app:selector="@drawable/wheel" />


</LinearLayout>

Answer 1

This might be because you are trying to use setColorListener on a view which is not even created. Note that you are using this method in onCreateView method. I suggest you to move those lines in onViewCreated method.

@Override
public void onViewCreated(View view, @Nullable Bundle savedInstanceState) {
    super.onViewCreated(view, savedInstanceState);

        ColorPickerView colorPickerView = (ColorPickerView) view.findViewById(R.id.colorPickerView);
        colorPickerView.setColorListener (new ColorListener() {
            @Override
                public void onColorSelected(ColorEnvelope colorEnvelope) {
                Toast.makeText(getActivity(), "Color:" + colorEnvelope.getColorRGB(), Toast.LENGTH_SHORT).show();
            }
        });
}