apps-android-commons/app/src/main/java/fr/free/nrw/commons/WelcomePagerAdapter.java

package fr.free.nrw.commons;

import android.support.annotation.Nullable;
import android.support.v4.view.PagerAdapter;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;

import butterknife.ButterKnife;
import butterknife.OnClick;

public class WelcomePagerAdapter extends PagerAdapter {
    static final int[] PAGE_LAYOUTS = new int[]{
            R.layout.welcome_wikipedia,
            R.layout.welcome_do_upload,
            R.layout.welcome_dont_upload,
            R.layout.welcome_image_details,
            R.layout.welcome_final
    };
    private static final int PAGE_FINAL = 4;
    private Callback callback;

    /**
     * Changes callback to provided one
     *
     * @param callback New callback
     *                 it can be null.
     */
    public void setCallback(@Nullable Callback callback) {
        this.callback = callback;
    }

    /**
     * Gets total number of layouts
     * @return Number of layouts
     */
    @Override
    public int getCount() {
        return PAGE_LAYOUTS.length;
    }

    /**
     * Compares given view with provided object
     * @param view Adapter view
     * @param object Adapter object
     * @return Equality between view and object
     */
    @Override
    public boolean isViewFromObject(View view, Object object) {
        return (view == object);
    }

    @Override
    public Object instantiateItem(ViewGroup container, int position) {
        LayoutInflater inflater = LayoutInflater.from(container.getContext());
        ViewGroup layout = (ViewGroup) inflater.inflate(PAGE_LAYOUTS[position], container, false);

        if (position == PAGE_FINAL) {
            ViewHolder holder = new ViewHolder(layout);
            layout.setTag(holder);
        }
        container.addView(layout);
        return layout;
    }

    /**
     * Provides a way to remove an item from container
     * @param container Adapter view group container
     * @param position Index of item
     * @param obj Adapter object
     */
    @Override
    public void destroyItem(ViewGroup container, int position, Object obj) {
        container.removeView((View) obj);
    }

    public interface Callback {
        void onYesClicked();
    }

    class ViewHolder {
        ViewHolder(View view) {
            ButterKnife.bind(this, view);
        }

        /**
         * Triggers on click callback on button click
         */
        @OnClick(R.id.welcomeYesButton)
        void onClicked() {
            if (callback != null) {
                callback.onYesClicked();
            }
        }
    }
}