AppIntroActivity.java

package com.airbnb.lottie.samples;

import android.os.Bundle;
import android.support.annotation.Nullable;
import android.support.v4.app.Fragment;
import android.support.v4.view.ViewPager;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.view.animation.Interpolator;
import android.widget.Scroller;

import com.airbnb.lottie.LottieAnimationView;
import com.matthewtamlin.sliding_intro_screen_library.buttons.IntroButton;
import com.matthewtamlin.sliding_intro_screen_library.core.IntroActivity;
import com.matthewtamlin.sliding_intro_screen_library.core.LockableViewPager;

import java.lang.reflect.Field;
import java.util.ArrayList;
import java.util.Collection;

public class AppIntroActivity extends IntroActivity {
  private static final float[] ANIMATION_TIMES = new float[]{
      0f,
      0.3333f,
      0.6666f,
      1f,
      1f

  };
  private LottieAnimationView animationView;
  private LockableViewPager viewPager;

  @Override
  protected Collection<? extends Fragment> generatePages(Bundle savedInstanceState) {
    return new ArrayList<EmptyFragment>() {{
      add(EmptyFragment.newInstance());
      add(EmptyFragment.newInstance());
      add(EmptyFragment.newInstance());
      add(EmptyFragment.newInstance());
    }};
  }

  @Override
  protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    animationView = (LottieAnimationView) LayoutInflater.from(this).inflate(R.layout.app_intro_animation_view, getRootView(), false);
    viewPager = (LockableViewPager) findViewById(com.matthewtamlin.sliding_intro_screen_library.R.id.intro_activity_viewPager);
    getRootView().addView(animationView, 0);
    setViewPagerScroller();

    addPageChangeListener(new ViewPager.OnPageChangeListener() {
      @Override
      public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {
        setAnimationProgress(position, positionOffset);
      }

      @Override
      public void onPageSelected(int position) {
      }

      @Override
      public void onPageScrollStateChanged(int state) {
      }
    });
  }

  @Override
  protected IntroButton.Behaviour generateFinalButtonBehaviour() {
    return new IntroButton.Behaviour() {
      @Override
      public void setActivity(IntroActivity activity) {
        finish();
      }

      @Override
      public IntroActivity getActivity() {
        return null;
      }

      @Override
      public void run() {
      }
    };
  }

  private void setAnimationProgress(int position, float positionOffset) {
    float startProgress = ANIMATION_TIMES[position];
    float endProgress = ANIMATION_TIMES[position + 1];

    animationView.setProgress(lerp(startProgress, endProgress, positionOffset));
  }

  private float lerp(float startValue, float endValue, float f) {
    return startValue + f * (endValue - startValue);
  }

  public static final class EmptyFragment extends Fragment {

    private static EmptyFragment newInstance() {
      return new EmptyFragment();
    }

    @Nullable
    @Override
    public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
      return inflater.inflate(R.layout.fragment_empty, container, false);
    }
  }

  private void setViewPagerScroller() {
    //noinspection TryWithIdenticalCatches
    try {
      Field scrollerField = ViewPager.class.getDeclaredField("mScroller");
      scrollerField.setAccessible(true);
      Field interpolator = ViewPager.class.getDeclaredField("sInterpolator");
      interpolator.setAccessible(true);

      Scroller scroller = new Scroller(this, (Interpolator) interpolator.get(null)) {
        @Override
        public void startScroll(int startX, int startY, int dx, int dy, int duration) {
          super.startScroll(startX, startY, dx, dy, duration * 7);
        }
      };
      scrollerField.set(viewPager, scroller);
    } catch (NoSuchFieldException e) {
      // Do nothing.
    } catch (IllegalAccessException e) {
      // Do nothing.
    }
  }
}