New Activity Not Opening

I'm an italian student developing an Android application with the latest version of Android Studio and with Android API 26 (Android Oreo). The application is very simple: 1. Main a

Solution 1:

<?xml version="1.0" encoding="utf-8"?><LinearLayoutxmlns:android="http://schemas.android.com/apk/res/android"android:id="@+id/materia"android:layout_width="match_parent"android:layout_height="wrap_content"android:orientation="vertical" ><ImageButtonandroid:id="@+id/imgButton"android:layout_width="match_parent"android:layout_height="120dp"/></LinearLayout>

~

publicclassItem_AdapterextendsArrayAdapter<Integer> {

    publicinterfaceItemListener {
         voidstartNewIntent(int position);
    }

    ItemListenerlistener=null;

    publicvoidsetItemListener(ItemListener item) {
        listener = item;
    }

    publicItem_Adapter(@NonNull Context context, int resource, @NonNull List<Integer> objects) {
        super(context, resource, objects);
    }

    @NonNull@Overridepublic View getView(finalint position, @Nullable View convertView, @NonNull ViewGroup parent) {
        if (convertView == null) {
            LayoutInflaterinflater= (LayoutInflater) getContext().getSystemService(Context.LAYOUT_INFLATER_SERVICE);
            convertView = inflater.inflate(R.layout.row, parent, false);
        }

    ImageButtonimgButton= convertView.findViewById(R.id.imageButton);

    imgButton.setOnClickListener(newView.OnClickListener() {
        @OverridepublicvoidonClick(View view) {
            if(listener != null) listener.startNewIntent(position);
        }
    });

    ImageViewimageView= convertView.findViewById(R.id.imageView);
    imageView.setBackgroundResource(getItem(position));

    return convertView;
    }

}

Solution 2:

Please declare all activities into AndroidManifest file.