MainActivity.java

package com.mcxtzhang.animdemo;

import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;


public class MainActivity extends AppCompatActivity {

    private CardFrontFragment mCardFrontFragment;
    private CardBackFragment mCardBackFragment;

    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        mCardFrontFragment = new CardFrontFragment();
        mCardFrontFragment.setOnChangeListener(new CardFrontFragment.onChangeListener() {
            @Override
            public void onChange() {
                flipCard();
            }
        });
        mCardBackFragment = new CardBackFragment();
        mCardBackFragment.setOnChangeListener(new CardFrontFragment.onChangeListener() {
            @Override
            public void onChange() {
                flipCard();
            }
        });
        if (savedInstanceState == null) {
            getFragmentManager()
                    .beginTransaction()
                    .add(R.id.container, mCardFrontFragment)
                    .commit();
        }
    }

    private boolean mShowingBack;

    private void flipCard() {
        if (mShowingBack) {
            getFragmentManager().popBackStack();
            mShowingBack = false;
            return;
        }

        // Flip to the back.

        mShowingBack = true;

        // Create and commit a new fragment transaction that adds the fragment for the back of
        // the card, uses custom animations, and is part of the fragment manager's back stack.

        getFragmentManager()
                .beginTransaction()

                // Replace the default fragment animations with animator resources representing
                // rotations when switching to the back of the card, as well as animator
                // resources representing rotations when flipping back to the front (e.g. when
                // the system Back button is pressed).
                .setCustomAnimations(
                        R.animator.card_flip_right_in, R.animator.card_flip_right_out,
                        R.animator.card_flip_left_in, R.animator.card_flip_left_out)

                // Replace any fragments currently in the container view with a fragment
                // representing the next page (indicated by the just-incremented currentPage
                // variable).
                .replace(R.id.container, mCardBackFragment)

                // Add this transaction to the back stack, allowing users to press Back
                // to get to the front of the card.
                .addToBackStack(null)

                // Commit the transaction.
                .commit();
    }
}